Journal of Environmental Protection, 2011, 2, 21-36
doi:10.4236/jep.2011.21003 Published Online March 2011 (http://www.SciRP.org/journal/jep)
21
Ambient Air Non-Methane Volatile Organic
Compound (NMVOC) Study Initiatives in
India - a Review
Amrita Talapatra, Anjali Srivastava
NEERI, Kolkata Zonal Laboratory, I-8, Sector ‘C’, East Kolkata Area Development Project, Kolkata, India.
Received September 14th, 2010; revised November 8th, 2010; accepted December 23rd, 2011.
ABSTRACT
Different aspects of Volatile Organic Compounds (VOCs) are being investiga ted in details by different research groups
in Indian institutes. The spectrum covers measuring technologies, source apportionment and variability studies, all
these are in due process of preparing a guideline for the sustainable development in terms of industrial, infrastructu ral
as well as overall growth of the country. Both the outdoor and indoor air quality has significant impact on human
health. With special concentration on BTEX and HAPs, the health related investigations are conducted as part of inter-
disciplinary studies o f environmental science. Newer technologies to remove VOCs under specific industria l and prac-
tical conditio ns are getting emerged a s a compa ratively new era . It addresses field s like ad sorption, conden sation, per-
vaporation, biodegradation and catalytic combustion. Besides, different kinds of biofilters have drawn significant atten-
tion nowadays. The final selection of appropriate technology depends on type and concentrations of VOCs, extent of
separation required and cost involved. All these technologies are although well studied, but could not be adopted for
regular commercial usage till da te. There is scope to explore new horizons as well as regular monitoring on the intro-
duced pathways to limit VOC emission in the ambient air. This review aims at a concise discussion on all the areas that
come under the umbrella of non-methane VOC technologies.
Keywords: VOC, India, BTEX, HAP, Biofilters, Catalytic Combustion
1. Introduction
Volatile organic compounds (VOC) are ubiquitous at-
mospheric species of both natural and anthropogenic
sources. These are wide range of chemicals including
aliphatic and aromatic hydrocarbons, alcohols, aldehydes,
ketones, esters and halogenated compounds sharing the
same characteristics of high volatility in the ambient en-
vironment and result in alteration of the chemistry of
atmosphere. On the global scale natural emissions of
nonmethane hydrocarbons (NMHCs) and VOCs exceed
anthropogenic emissions. Among the natural sources,
vegetation is the dominant source. Oceanic and microbial
production of these species is minimal as compared to
other sources of input. On the other hand, anthropogenic
sources are the result of urbanization and industrializa-
tion. This rapid urbanization and industrialization, at
some places in a most unorganized way, is the general
picture in developing countries around the world. The
main concern of VOCs is the role they play in the forma-
tion of ozone and photochemical smog and increased risk
of cancer. Thereby it is quite evident that although in
rural areas natural vegetation causes VOC emission, due
to lower NOx concentration, O3 production is less; which
is not the case in urban atmosphere, where due to the
industrial and vehicular pollution the relative concentra-
tion of NOx reaches up to a level so that it easily contrib-
utes to production of O3 even in small concentration of
NMHCs. In polluted areas with relatively high concen-
tration of NOx, photochemical oxidants of NMHCs, initi-
ate a complex series of photochemical reactions that lead
to the production of O3 and other secondary oxidant pol-
lutants [1]. The emission of VOCs thus have much more
detrimental effect in urban areas and the percentage con-
centration of VOCs in ambient air, their source profile
identification and effect on health due to exposure should
be well understood to undertake a successful planning of
metropolis or establishment of industrial belt.
India being a leading giant among developing coun-

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review 22
tries, huge pressure from different domestic and interna-
tional forums is put on to formulate rules and regulations
towards VOC control along with many other ecofriendly
footsteps. Considering the global scenario, not even EPA
proposed any standard for ambient VOCs. But the US
Occupational Safety and Health Administration (OSHA)
and World Health Organization have come up with some
guidelines for these air pollutants, but these are recom-
mendations and not compulsory for governments to fol-
low [2]. Although started late, but from last decade in
Indian continent, several initiatives, largely in academic
sector have taken place regarding measurement and con-
trol of VOCs. This review is meant to accommodate the
various areas of published work from Indian Institutes
based on VOCs monitoring in Indian cities.
2. National Level Regulations
Central Pollution Control Board India has regulated
Benzene and Benzo(a)Pyrene by including them in Na-
tional Ambient Air Quality Standard since November
2009. Standards for Benzene and Benzo(a)Pyrene are
mentioned in Table 1.
Corresponding vehicular exhaust norms and auto fuel
quality specifications also have been put forward to im-
pose certain restrictions. Vehicular exhaust norms are in
effect from 1991 and the current scenario specifies com-
bined value for hydrocarbon and NOx to be respectively
0.35 and 0.18 g/km for Bharat Stage III and IV passenger
cars, whereas the values are 1.5 and 1.0 for 2/3 wheelers
(Bharat Stage II and III respectively). Heavy Diesel ve-
hicles are allowed upto 1.1, 1.6 and 0.96 g/km hr of hy-
drocarbons for Bharat stage II, III and IV respectively.
Maximum permissible amount of benzene in gasoline has
been specified to be 1% by volume in the year 2010 con-
siderably lowering it from 5% in the year 1996.
3. Monitoring and Measurement of VOCs
Air quality monitoring requires detection in a very low
concentration (ppb range) for several types of VOCs.
This necessitates sufficient sensitivity to trap the com-
pounds of interest for subsequent analysis using appro-
priate chromatographic technique [3]. Generally two ba-
sic principles are being followed e.g., active sampling
that includes pumping of controlled air flow into the
sampler for a specific sampling period and thereafter air
drawn-in is passed through the adsorbent for adsorption
of pollutant being monitored; whereas passive sampling
is dependent on diffusion of pollutant from bulk air to the
adsorbent directly. Therefore the ideal adsorbents ex-
pected to possess characteristics like large accessible
pore volume, no catalytic activity, hydrophobicity, high
thermal and hydrothermal stability and easy regeneration
properties. In general, the research papers have men-
tioned activated charcoal as the adsorbing media, al-
though there have been considerable studies towards cost
effective alternative new materials like surface modified
zeolites, product synthesized from fly-ash [3-5]. Target
VOCs specified in USEPA Compendium method TO-14
or TO-17 were generally monitored using adsorption,
thermal desorption and subsequent analysis on GC-MS
or GC-FID [5-7].
4. Ambient Air Concentration of VOCs
4.1. Anthropogenic Sources
For assessing anthropogenic sources of VOCs, urban
atmosphere is the target environment because of high
level of pollution. In India the capital city Delhi and three
other metropolitan cities like Mumbai, Chennai and
Kolkata are therefore the natural selection in almost all
the cases. Large population necessitating highways, busy
traffic network and thereby refueling stations, high rise
office, residential and commercial complexes forbidding
easy air passage and nearby industrial hubs keep on add-
ing versatile sources of VOCs in these cities. Being situ-
ated at different geographical locations the cities as a
whole represent the generic atmospheric pattern of the
country.
Table 1. National ambient air quality standard.
Concentrations in ambient aira
Pollutant Industrial, Residential,
Rural and Other Area Ecologically Sensitive Area (notified by Central Government)Methods of Measurement
Benzene (C6H6) µg/m3 5 5
-Gas chromatography based continuous analyzer
-Adsorption and Desorption followed by GC
analysis
Benzo(a)Pyrene
(BaP)-particulate phase
only, ng/m3
1 1
-Solvent Extraction followed by HPLC/GC
analysis
aT
ime weighted Average-Annual.

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review23
 Kolkata: The Kolkata metropolitan area is a mega
city of 1246 km2 with a high vehicle density (5685
per km2). In December 2002, the number of vehi-
cles registered with the Public Vehicles Depart-
ment was about 0.8 million, with 40 000-50 000
vehicles being added each year (Asian Develop-
ment Bank, 2005); In terms of traffic, local vehi-
cles are supplemented by those coming from sub-
urbs. To service the fleet, a large number of work-
ers are associated with fueling [8].
 Delhi: Delhi, the National Capital Territory of In-
dia, has a geographic area of 1483 km2 stretched in
east–west width approximately 51.9 km and north-
west width approximately 48.48 km with a popula-
tion 13.79 million. Delhi is situated at latitude of
28˚24′ 17″ to 28˚53 and the longitude of 76˚20′37″
to 77˚20′37″ with an altitude of 216 m above mean
sea level in the semi-arid zone of India. To the
north the Himalayas are at a distance of just 160
km and to the south are the central hot plains. To
the west of Delhi is the Great Indian Desert (The
Thar) of Rajasthan and cooler hilly regions to the
northeast. The climate of Delhi is mainly influ-
enced by its inland position and the prevalence of
continental air during the major part of the year.
Extreme dryness with an intensively hot summer
and cold winter are the main characteristics of the
climate. The mean annual rainfall in Delhi is 71.5
mm. About 81% of the annual rainfall is received
during the monsoon months. January is the coldest
month with the mean daily maximum temperature
at 21.3˚C and mean daily minimum at 7.3˚C. May
and June are the hottest months with temperatures
touching 46 - 47˚C. The average annual tempera-
ture ranges between 22˚C and 25˚C. The air in
Delhi is dry for most of the year, with very low
relative humidity from April to June and markedly
higher humidity in July and August, when weather
conditions are oppressive. Temperature inversions
are common in winter [5,6,9,10].
 Mumbai: Mumbai is located at the coast of Arabian
Sea on the West coast of India. Mumbai is one of
the largest metropolitan cities of the World with its
population of approximately 12 million in 2001.
Mumbai is also one of the fast developing me-
tropolises with variety of activities, viz. commer-
cial, residential, industrial, port activity, etc. The
total number of registered vehicles in 2001 is about
10,29,563. Two wheelers form a major portion of
vehicular population, followed by cars and jeeps.
Mumbai is hub of commercial and industrial activ-
ity. It is a port town. Mumbai has a tropical sa-
vanna climate with relative humidity ranging be-
tween 57% and 87%, and annual average tempera-
ture of 25.3˚C, with a maximum of 34.5˚C in June
and minimum of 14.3˚C in January. The average
annual precipitation is 2078 mm, with 34% of total
rainfall occurring in July. The prevailing wind di-
rections are from West and northwest, with West
and southwest shifts during monsoon. Some east-
erly component is observed during winter [7,11].
Although parts of the cities are planned, in maximum
areas there is no clear distinction of sectors like residen-
tial or industrial and thus generating complex air shed
profile. Again petrol pumps situated nearby the roads add
up evaporative emission to exhaustive emission. Cer-
tainly all these emissions pollute indoor air also. Thereby
the traditional monitoring system divides the localities in
specific zones but the source profiles can never be com-
pletely separated according to different activity centers.
In recent years ambient air quality in these cities has
been thoroughly studied by different research groups, but
the subsequent source apportionment studies reveal the
emission nature of the cities more specifically [9,10].
4.2. Source Profile Identification and Analysis
Rapid economic and urban population growths have
triggered a series of challenges to the endeavors of
maintaining the clean air [11]. New pollutants are being
increasingly recognized and point to sources, which are
of inevitable use in day-to-day modern life. Air pollution
sources have grown and so also the pollutants. In order to
devise effective air quality management programmes to
control VOCs, it is necessary to know the sources of
VOCs in the region of concern. Receptor models assess
contributions from various sources based on observations
at sampling sites. Chemical mass balance (CMB) recep-
tor model have been used to apportion different fractions
of VOCs in several urban areas. Principal component
analysis (PCA or factor analysis), multiple linear regres-
sion analysis (MLR) and all other approaches are based
on fundamental mass balance concept. CMB modeling
approach using multiple linear least squares regressions
was used to identify the probable sources of VOCs. The
foremost step to apply CMB is to judge the applicability
of the model to the study with regard to source composi-
tions being constant over a period of sampling. In a com-
plex urban airshed, some source profiles were collinear
with the measured species. This leads to the average ab-
solute errors of approximately 30% even when coeffi-
cients of variations in source profiles reached 50%.
Within last five years, study on source apportionment
of major cities of India has been performed with special
focus on petrol retail distribution centers. The broad per-
spectives of the cities are clearly understood from the
findings.

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review 24
 Evaporative emissions dominate in Mumbai [12].
Oceanic emissions also contribute significantly to
TVOCs in Mumbai. Sources other than exhaust of
petrol driven vehicles, contribute to a large extent
to benzene concentration in ambient air. Abnor-
mally higher B/T (concentration ratio between
benzene and toluene) of 11.74 at petrol pumps in-
dicates adulteration of fuels as well.
The presence of chlorinated compounds in Mumbai
may be attributed to emissions from the sea. The concen-
trations of C6-C10 hydrocarbons were more than that for
C2-C5 at the industrial sites whereas C2-C5 hydrocar-
bons were more at refineries [13].
 Emissions from diesel internal combustion engine
were found to be a dominating source of VOCs in
ambient air of Delhi ranging between 26 to 54%
[14]. Large number of diesel generator sets is used
in Delhi in residential, commercial and industrial
areas as a backup to power supply. But showing
effect of intervention in use of petroleum and diesel
fuel and shift to CNG, benzene emission reported
is comparatively low in Delhi.
Sludge emissions consist of emission from sewage
treatment plants and open defecation is detected in both
the cities as these are common practice in everywhere in
India.
 Vehicular exhaust emissions from adjacent road-
ways are the greatest contributor (39.0 ± 15.7%) in
Kolkata petrol pumps situated on the curbside of
busy roads with high traffic density [8]. Contribu-
tions of exhaust from light duty diesel driven, as
well as petrol vehicles, (the majority of the petrol
driven light duty vehicles were without catalytic
converters), also contributed significant amounts of
VOCs (10.3 ± 5.2% and 6.5 ± 6.4%, respectively)
around the petrol pumps.
In general, in all these three metro cities other sources
like automotive refinishing, repairing and washing ser-
vice facilities in the adjoining garages inside the petrol
pump premises, petrol spilled during refueling, automo-
tive painting, repairing works, degreasing, fugitive emis-
sions from the petrol storage facilities, automotive con-
sumer products, automotive tyres been recognized.
Compiling from different sources the emission pattern
of these 3 cities can be summarized as in Table 2.
4.3. Indoor VOC Studies
Studies on indoor pollution are important since an aver-
age person spends more than 80% of the daytime in the
indoor environment either in the home or in the work
place [19]. The poor quality of indoor air has been linked
to a number of symptoms, which the World Health Or-
ganization has defined as Sick Building. These symp-
toms include headache, nausea, irritation of the eyes,
mucous membranes and the respiratory system, drowsi-
ness, fatigue and general malaise. Poor air quality in of-
fice premises produces discomfort, decreases worker’s
efficiency and increases absenteeism. Conversely, im-
proved air quality can lead to improved productivity.
Among the Volatile Organic Compounds VOCs, benzene
is confirmed as a human carcinogen. The other VOCs,
such as hexane, heptane and octane can affect the central
nervous system. Therefore, the studies related to indoor
air pollution due to VOCs are of significance as they are
directly related to the health of human beings in day-to-
day life.
The main sources of VOCs in the indoor environment
are building materials, furnishing, cleaning compounds,
dry cleaning agents, paints, varnishes, glues, aerosol
propellants, refrigerants, fungicides, germicides, cosmet-
ics and textiles. Human activities such as cooking,
cleaning and smoking also contribute to VOCs in the
indoor environment. Many workers have carried out
studies on VOCs in indoor air in residences and office
premises and concentrations of VOCs have been found to
vary widely from place to place. Besides indoor sources,
industrial emissions, exhaust from vehicles driven on
diesel and gasoline are some of the anthropogenic
sources of VOCs in the outdoor environment which con-
tribute to indoor VOCs; it has been observed that the rate
of indoor pollution was affected by the direction of wind.
Methods for monitoring VOCs in indoor air may be
classified as one of two types viz. analytical methods
which detect and quantitate pollutants on site and collec-
tion techniques which concentrate organics on some type
of sorbent for later analysis [20]. Solid sorbents are the
materials most commonly employed for collection of
vapour phase organics. Comparing VOCs in different
indoor environments as well as with corresponding
nearby outdoor observations show large variations in
concentrations. The xylenes and toluene were the main
contributors for indoor levels of a recently renovated hall
having polished and varnished furniture. This location
showed a significant concentration of these compounds
even a week after the polishing and varnishing. The main
contributor for the kitchen environment was benzene.
The laboratory environment showed high indoor/outdoor
ratios (I/O) for benzene and hexane, mainly due to the
usage of these solvents. The indoor levels of VOC con-
centrations were significantly high in locations where
painting activity continued and the magnitude of concen-
trations depended upon the type of paint being used. The
I/O ratio of total C6-C10 compounds was also signifi-
cantly high in these locations. In the rooms where ciga-
rette smoking is a constituent, the concentration of ben-
ene depends on the size of the room, ventilation rate, z

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review 25
Table 2. Emission pattern of metro cities in india.
Region Highest Recorded TNMVOCLocation Benzene: Toluene Type of emission
138-214 µg/m3 Residential
362-462 µg/m3 Commercial
311-472 µg/m3 Industrial
666-790 µg/m3 Traffic
Mumbai [7,11,12]
1206-1372 g/m3 Petrol pumps
11.74 Evaporative
92-162 µg/m3 Residential
1167-1369 µg/m3 Commercial
361-656 µg/m3 Industrial
541-733 µg/m3 Traffic
Delhi [9,10,12,14-16]
560-819 µg/m3 Petrol pumps
8.11 Diesel engine exhaust
43.0-546.1 µg/m3 Residential cum Commercial
83-456.1 µg/m3 Industrial
177.6-745.2 µg/m3 Traffic
Kolkata [8,17,18]
128.3.1173.6 µg/m3 Petrol pumps
3.5 Vehicular Exhaust
number of people smoking, the number of cigarettes
smoked, etc. All the VOCs found in non air conditioned
indoor air was also found in air conditioned indoor air
and air conditioned indoor air was found to be contami-
nated by some additional VOCs.
 Inside Car: Fabrics, upholstery, carpets, adhesives,
paints, cleaning materials contribute towards in-
vehicle VOCs [21]. Malfunctioning in the automo-
bile system emits the VOCs 10-30 times more than
usual vehicle and such excessive emission elevates
in-vehicle concentration of gasoline derived com-
ponents. Thereby, total time spent in vehicle is of
much concern as total dose of VOC inhaled affects
human health and thus the study becomes very
much relevant in the current scenario of developed
as well as developing countries. The two com-
monly used vehicles in India (Maruti Zen and Ma-
ruti 800) were considered for estimation of VOCs
inside parked car by Patil S. et al. and successful
monitoring was done to come up with highest con-
centration of Benzene in both the cases caused by
unleaded petrol in the vehicle. It was suggested
earlier that even when all the windows were closed
tightly, the air turnover rate in automobile was 9
times higher when vehicle was traveling at 40 km/h
than when it was parked.
4.4. Variability of VOC in Atmosphere
The variability of pollutants is an important factor in de-
termining human exposure to the chemicals. Variability
can be divided into measured, spatial, temporal or sea-
sonal and temporal-spatial interaction components [6].
Information on variability is required to determine the
optimum sampling period, frequency to capture short-term
peak concentrations, optimum number and locations of
monitoring sites for population exposure assessment.
Knowledge of variability of concentration within each
microenvironment and between similar microenviron-
ments is important in design of monitoring programmes
and in the application of exposure models.
Chemicals with observed concentrations to show low
relative standard deviation are supposed to uniformly
distribute in space. For others, measurement variability
can arise from sampling and analysis methods, which can
be detected by collection of duplicate samples; actual
atmospheric concentrations variability also results in
concentration variations. It has been established that al-
though complexities are introduced by diurnal variations
in local sources, local effects of wind, other meteoro-
logical conditions and local factors; maximum variability
is introduced due to temporal and temporal spatial inter-
action. A recent study, although centered on urban at-
mosphere of Delhi, can be generalized for Indian climate,
exhibit clear seasonal variations of the inter-species ra-
tios indicating differential reactivity of the VOC species
in different seasons. Observed seasonal trends can be
addressed by the seasonal characteristics of the prevail-
ing meteorology, variations in the source strength and,
most importantly, the availability of OH radical and in-
solation that take care of the removal process of the VOC

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review 26
species from the atmosphere. The meteorology in Delhi
shows an explicit winter and summer characteristics. In
the winter months calm conditions and high stability of
the atmosphere prevails, which hinder the pollutants
from dissipating faster. Temperature inversion, which is
a common phenomenon in the winter months and low
mixing heights do restrict dilution process of the pollut-
ants. Thus in the winter months the pollutants generally
show a higher level of concentration. An enhanced emis-
sion of aromatics is also reported due to cold start of
gasoline powered vehicles in the winter months. In In-
dian cities during winter, slum dwellers ignite biomass
including wood waste and other organic refuse for heat-
ing that also contribute to VOC loading of the atmos-
phere [10]. In contrast, the summer months in Delhi ex-
perience higher mixing height and an unstable atmos-
phere in addition to which there might be several occa-
sions of sandstorm, locally known as andhi [5]. Mete-
orologically these factors favor to better mixing and easy
dissipation of the pollutants leading to their lower levels
in the atmosphere. Delhi records more insolation during
summers which helps in the photolysis of species like
ozone, aldehydes etc., leading to the formation of OH
radical. The reaction of terpene with ozone also leads to
the formation of OH radical. Thus in the summer months
high level of OH concentration could prevail in the at-
mosphere of Delhi, which plays the key role in the at-
mospheric clean up and degradation process of the aro-
matic VOCs. The study shows a clear seasonal profile
with a unimodal pattern for the summer months. In in-
dustrial areas toluene and xylene profiles are bimodal
indicative of enhanced evaporation of toluene from in-
dustrial units, vehicular service stations, electric motor
winding and waste decomposition at waste dumping
lands around the sampling location in hotter months.
4.5. BTEX
Benzene, toluene, ethylbenzene and xylene (BTEX) form
an important group of aromatic Volatile Organic Com-
pounds (VOCs) because of their role in the tropospheric
chemistry and the risk posed by them to human health.
BTEX constitute upto 60% of non-methane VOCs and
can be considered as an efficient indicator of organic
compound pollution from road traffic [5]. The reaction of
the BTEX with hydroxyl radicals (OH) and/or nitrate
(NO3) radicals serves as the dominant degradation proc-
esses for aromatic VOCs in the atmosphere. The result-
ing products contribute to secondary organic aerosol
(SOA) formation by nucleation and condensation. In the
presence of NOx, aromatic VOCs in general, react with
OH radicals to form ozone; thus modifying the oxidizing
capacity of the atmosphere. Ozone formation potential of
VOCs can vary by virtue of differences in their reactivity
and structure. This has led to the development of scales
of so called ‘reactivity’ or “ozone formation potential”
for VOC. For ranking of the BTEX with respect to their
contribution to O3 formation, MIR (Maximum Incre-
mental Reactivity) coefficient is a popular means which
has been used in a recent study on BTEX concentration
in ambient air of Delhi along with rate constants of
VOC-OH reactions to assess the ozone formation poten-
tial of BTEX compounds. MIR can be defined as the
amount (in grams) of ozone formed per gram of VOC
added to an initial VOC–NOx mixture, indicating how
much a compound may contribute to the ozone formation
in the air mass. These unitless MIR coefficients are in-
tended for use in relatively high NOx conditions, which
may be used as an important tool in ozone control pro-
grams. The reactivity of VOC with OH radical depicts
the ability of the hydrocarbon to form higher oxidized
products like aldehydes, ketones, acids, organic peroxy
radicals, etc. A good mutual correlation among the spe-
cies indicates that they might primarily originate from
the same source and a good mutual correlation between
ethylbenzene and xylene indicates that they might possi-
bly originate from gasoline vehicle and gasoline stations.
Based on the MIR scale, xylenes are the most dominant
contributor to ozone formation among BTEX. Toluene is
the second largest contributor to ozone formation. Ozone
formation potential of benzene is minimal though it is the
most hazardous species among BTEX.
Efforts to reduce lead content of the fuel gasoline and
to maintain the octane number have led to an increase in
benzene and other aromatic carbons in gasoline. Use of
tetra ethyl lead (TEL) in fuel was phased out between
1994 and 1998 in major cities in India [22,23].
There is a general consensus that for well maintained
vehicles, the majority of the exhaust fumes which build
up in the vehicle interiors, come from the exhaust fumes
of surrounding vehicles either naturally or by ventilation
and not from the vehicle itself. The elevated VOC inside
the vehicles without catalytic converter used in the study
is associated with internal leakage of engine evaporative
emission and/or vehicle exhaust emission through body
cracks into the vehicle interior due to the fairly old vehi-
cle age (> 10 years), poor body conditions, high mileage
and poor car maintenance. On the other hand, newer
catalyst equipped cars marketed after 2001 respect
Bharat Stage II norms (equivalent to European Union
Emission Standard, EURO II) and have efficient emis-
sion control with less combustive VOC emission.
A two phase (phase I: 2001-2002 & phase II: 2003-
2004) monitoring made inside and in the immediate out-
side of passenger cars fitted with and without catalytic
converters using different types of fuels, along two con-
gested urban routes. During Phase I of the study, the

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review27
benzene content in gasoline was 5% and the mean con-
centration of in-vehicle benzene in cars without catalytic
converter was found to be as high as 721.2 μg/m3. In
Phase II when the benzene content was reduced to 3%
and with modified engine type, the mean in-vehicle ben-
zene concentration was reduced to 112.4 μg/m3. The
in-vehicle concentration varied with engine type and age
of the vehicle. Roadside ambient mean concentration of
benzene was 214.8 μg/m3 and 30.8 μg/m3 in Phase I and
Phase II respectively. The same study showed, the value
was higher than the cars fuelled by diesel (0.78 for ben-
zene and 0.70 for toluene) or LPG (0.95 for benzene and
0.94 for toluene). It has been established earlier that die-
sel fuelled vehicles are primarily impacted by the pene-
tration of roadway air into the cabin while for the gaso-
line fuelled vehicle, the exhaust emission is rich with the
target VOCs due to the presence of these components in
the gasoline. The increase in T/B ratio inside and outside
of all types of cars in Phase II along with roadside static
value reflects the positive effect of decreased level of
benzene in fuel as well as presence of different commer-
cial and industrial sources of toluene in urban areas.
Toluene level was not significantly different in Phases I
and II. Thereby it can be pointed out, that Commuters in
urban Kolkata travelling in cars are more exposed to
BTEX compared to other cities of the world, not only
because of inadequate emission control, but also due to
insufficient road space and slow driving speed.
Another similar study on five different microenviron-
mental regions in Mumbai viz., petrol pump, traffic junc-
tion, arterial road, highway and parking areas has also
concluded that the concentration of benzene in air cannot
be related to only the number of vehicles, but along with
ventilation available, age and type of vehicle, meteorol-
ogy also contribute significantly. High concentrations at
traffic junctions and parking areas are due to startup
emissions of engines; whereas at repair garages the use
of solvents for cleaning contributes to high benzene con-
centrations [24,25].
Unlike Kolkata no declining trend in benzene concen-
tration has been reported in Mumbai, which can be due to
the industrial releases, a significant contributor in Mum-
bai, does not show any evidence of coming down. Be-
sides vehicles fitted with catalytic converter, two wheel-
ers, three wheelers and four wheelers without catalytic
converter still form a significant part of vehicle inventory
in Mumbai and thereby not impacted much till the time
of study.
All these methods used to measure concentration of
benzene are mainly based on passive diffusion or
pumped diffusion with a very low flow rate. Averaging
time of measurements varies from few minutes for online
system to few days in case of passive diffusion. Like
other classic pollutants no averaging time is suggested
for monitoring of benzene. The volume of air sampled
varies from 0.5 to 101 over the sampling period. The
measurements made at the traffic junction do not repre-
sent a well-mixed atmosphere. Therefore an attempt was
made to include dispersion parameters into multimedia
model to predict concentrations of benzene using multi-
media mass balance model considering emission into air
in a micro spatial scale defined as area of approximately
around traffic intersections and highways as compared to
regional, continental and global scales used [26]. Al-
though the model overestimates the concentrations, but
due to fairly good agreement with observed values can be
used as a tool to act as an indicative value. In microenvi-
ronment 0.1% of benzene is distributed on road surface
and 0.3% on urban soil and most of the benzene 99.6%
remains in the air whereas, 97.2% of benzene remains in
air phase of the environment, small amounts get por-
tioned into agricultural soil (1.4%), other soils (0.9%)
and sea water (0.5%) in regional system. The predicted
concentration of benzene in air at regional scale is 0.267
µg/m3 and half life time in air was estimated at 10.5 days.
Based on their photochemical reactivity towards hy-
droxyl radical, the concentrations of the VOCs were
scaled to formaldehyde equivalent, which showed that
the high molecular weight carbonyls and xylenes con-
tribute significantly to the total OH-reactive mass of the
VOCs [27]. Intense solar radiation in tropical climate
increases secondary formation of the low molecular
weight carbonyls by photo-oxidation of VOCs especially
BTEX and thereby governing principal pathway for the
disappearance.
 Biomarker for Benzene: Benzene after inhalation,
excreted rapidly in urine as conjugate phenol and
dihydroxy phenol and it is comprised of almost
one-third of retained content [28]. Thus phenol be-
ing a metabolite of benzene, its excretion has been
traced as marker of short-term benzene exposure.
Being a painless, easy to obtain and low-cost proc-
ess the urinary phenol technique is applied on
workers (non-smoker and non-alcoholic consump-
tion) of petrol-filling stations of peri-urban areas in
eastern India. The concentration of phenol was de-
termined by aminoantipyrine method and found to
vary between 5.14 + 1.63 and 11.66 + 1.92 (before
and after work shift) compared to 2.09 + 0.62 and
3.28 + 0.76 for control sample.
5. Natural Sources
Considering abatement of air pollutants, decrease in am-
bient temperature by evapotranspiration, sequestering of
carbon dioxide and subsequent processes to march to-
wards better air quality plantation in urban and industrial

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review 28
areas have been a common trend nowadays [29-31].
Many vegetational species emit VOCs, particularly iso-
prene, which is highly reactive and having high photo-
chemical ozone creation potential (POCP) value, and
terpenes, responsible for the formation of acid rains;
formation of secondary aerosols in the atmosphere af-
fecting radiative balance of earth is another major impact
caused by biogenic VOCs. Isoprene emission constitutes
about 40% of all biogenic hydrocarbons emitted into the
atmosphere from vegetation. Using Dynamic flow en-
closure technique foliar emission of a series of local plant
species in Delhi has been thoroughly studied by Padhy et.
al. Diel, seasonal and interspecies variations have been
recorded and the trend was analyzed in order to prepare
the total annual biogenic VOC emission from India.
Testing saplings of about 2 years old no isoprene emis-
sion detected during night time from any species, but
starts early in the morning and gradually increasing
reaching peak during noon and afternoon. The initiation
of emission shifted with the change in season, recording
the most delayed during winter ensuring the dependency
of isoprene emission on temperature and light. It is al-
ready observed that isoprene emission reaches the
maximum at light intensities in saturated photosynthesis
and increases with the rise in temperature up to certain
point and thereafter it rapidly declines. The maximum
amount of isoprene was emitted in the rainy season (8.5 +
8.3 μg·g-1 leaf dry weight·h-1) and lowest during the win-
ter (3.9 + 6.8 μg·g-1 leaf dry weight·h-1). Unlike isoprene
-pinene emissions were not confined to daytime only.
The rate of emission for -pinene appears to be inde-
pendent of light but increase exponentially with tem-
perature. Considering all kind of emissions Bougainvilea
spectabilis and Nerium indicum are recommended for
creating hedge; Acacia Arabica, Alstonia scholaris,
Azadirachta indica and other seven species have been
suggested for tree plantation.
6. Hazardous Air Pollutants and Health
Issues
The United Nations estimated that over 600 million peo-
ple in urban areas worldwide were exposed to dangerous
levels of traffic-generated air pollutants [2]. Air pollution
and its public health impacts are drawing increasing
concern from the environmental health research commu-
nity, environmental regulatory agencies, industries, as
well as the public. The quality of the air, both indoors
and outdoors, is closely related to morbidity and mortal-
ity from respiratory and cardiovascular diseases. Many of
the VOCs are included in the list of 188 hazardous air
pollutants (HAPs) identified by USEPA. (HAPs) are the
pollutants known or suspected to cause cancer or other
serious health effects or adverse environmental effects.
HAPs have a potential to partition into different compo-
nents of environment, and some of them have considera-
bly long lifetime in one environmental component or
other making them persistent in ecosystem. Persistence is
an important attribute for determining the overall human
health and ecological impact of a chemical released to
the environment. Persistent pollutants pose a greater po-
tential concern per unit release because they cannot be
rapidly removed from the environment. An appropriate
measure of persistence is the characteristic time a chemical
remains in the environment. This can theoretically be
determined by finding the overall decay rate of a pollut-
ant in a closed defined landscape system, calculation of
which requires both the mass distribution among envi-
ronmental media and media specific half-life.
Multimedia models based on concept of fugacity, has
been successfully used to determine whether the pollut-
ant can have a local, regional or global scale impact de-
pending on the characteristic spatial scale [32]. The TaPL3
model, while applied for Thane Belapur Industrial Area
(TBIA), divided the environment in five well-mixed
compartments like atmosphere, creek, soil, sediment and
vegetation. The model mathematically calculates the en-
vironmental persistence; Travel Distance in Air (Long
Range Transport Potential or LRT) defined as the poten-
tial for the chemical to be subject to long range transport
and the average hoping value H, representing the average
number of hops experienced by the chemical from one
compartment to another. Carbon tetrachloride scored the
highest (0.99) in average no. of HOPs and the lowest
value (0.001) was recorded for Formaldehyde. Persis-
tence hours value for Naphthalene is the highest (3.23E +
09) whereas minimum value (51.6) is registered for For-
maldehyde.
HAPs have varying types of human health effects, car-
cinogenic and non-carcinogenic, depending upon the
chemicals involved, concentration and exposure time.
Some of them have both toxic and carcinogenic effect.
The toxic effect can be acute (short-term severe health
effect) or chronic (long-term persistent health effect).
Toxicity is often evident in a shorter length of time than
the carcinogenic effect. The potential health effects of
non-carcinogens range from skin irritation to life-short-
ening. Carcinogens cause or increase the incidence of
malignant neoplasms or cancers. Risk characterization
integrates the information on hazard identification, dose
response assessment and exposure assessment to develop
a qualitative and quantitative estimate of the likelihood
that any of the hazards associated with the chemical will
be realized in exposed people. Risk score system helps to
identify environmental releases of toxic chemicals that
are likely to pose greater risk to human health. This sys-
tem adjusts the amount of a chemical that is released

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review29
using a weighing factor (a chemical’s toxic equivalency
potential (TEP)) so that chemical releases can be com-
pared on a common scale that takes into account differ-
ences in toxicity and exposure potential. The study shows,
the workers and residents of TBIA are exposed to levels
of HAPs which have potential for adverse impact on their
health. The current study considered output of TaPL3 to
be the input of concentrations of HAPs in different com-
ponents of environment to calculate toxicity profile. Tra-
ditionally, exposure assessment is focused on ambient air
pollution levels, which can be easily obtained by estab-
lishing several fixed monitoring sites in the region of
interest. Due to spatial variations of the pollutant levels
in the study areas, usually exposure monitoring data ob-
tained from these limited number of fixed-sites are not
accurate enough for epidemiologic studies.
An alternative for this is the adoption of traffic indica-
tors (population density and traffic intensity) and geo-
graphic information system (GIS), especially when traf-
fic-related exposure is the main focus. By collecting traf-
fic indicator information, personal exposure can be esti-
mated. This method is suitable for long-term exposure
assessment for large populations in urban areas. It is an
effective method when the main goal is to estimate the
exposure profiles of a certain area, and it is better in ad-
dressing spatial variations of air pollution levels in a cer-
tain area than fixed-site monitoring. The introduction of
portable measuring equipment made personal exposure
assessment feasible by addressing exposure issues for
high risk populations like traffic policemen and drivers.
But this technique is expensive and not suitable for large
population-based study and long-term monitoring.
This personal monitoring system has been taken place
in atleast two major studies of VOC exposure based on
Kolkata city [21,33]. Kolkata is one of the most populous
metropolitan cities of the world with significant com-
muter flows and thereby large number of staffs is en-
gaged in transport buses as well as petrol pumps. Two
different studies have been conducted to assess the
in-vehicle and pumping station exposure of VOCs for the
workers involved. For the first case, exposure to VOCs is
found to depend on the condition of the engine, the qual-
ity of fuel used, and on traffic density. The mean benzene
exposure of drivers and conductors are 527.3 and 154.2
µg/m3 respectively. The concentrations of the VOCs,
benzene, toluene, o-xylene and p-xylene were found in
the ranges, 147 - 3465.3, 42.5 - 3770, 108.1 - 2347.8 and
56.6 - 437.8 µg/m3 respectively. The wide ranges may be
because of the poor conditions of engines buses sampled.
They may emit more VOCs due to fuel loss or due to
contamination of the fuel used. Drivers mean exposures
to benzene, toluene, and o-xylene were found to be
higher than for conductors. During the study, buses were
randomly selected, the days on which old model bus was
selected the VOC values shooted up.
The level of exposure in petrol pumps is largely de-
pendent on the technical specifications of gasoline, espe-
cially its benzene content, and to the emission control
technology, such as vapor recovery systems in operation.
Monitoring of the service station workers revealed that
the average exposure level for benzene and toluene were
3.9 and 5.5 fold higher than the ambient air. The inte-
grated lifetime cancer risks due to benzene, ethylbenzene,
formaldehyde and acetaldehyde and the overall hazard
index due to chronic exposure to some hazardous volatile
organic compounds are 1.48E-04 and 2.3 indicating the
probability of cancer as well as chronic health effect on
the workers exposed.
7. Removal Initiative
Considering anthropogenic emission due to the inherent
presence of VOCs in the products (chemicals), the con-
trol strategy for VOCs emission distinctly differs from
that for the common urban pollutants such as NOx, SO2,
and CO in that the former usually requires an end-of-pipe
control strategy. The substitution of raw materials, equip-
ment and process modification are applicable mostly in
control of the later pollutants, whereas VOCs control
methods include condensation, adsorption, catalytic oxi-
dation, thermal oxidation, air stripping and biological
treatment. There are findings like change in resistivity of
polymeric nanomaterials [35], which can be used as
sensing the presence of VOCs, but the elimination efforts
has received much attention. The selection of appropriate
technology depends on type and concentrations of VOCs,
extent of separation required and cost involved [35,36].
7.1. Adsorption/Condensation of VOC in Air
Medium
While condensation using N2 at cryogenic temperatures
was recognized as the most effective and commercially
suitable technique, adsorption is considered as the state-
of-art technology having immense potential for VOC
control. The keyword of an adsorption process is a po-
rous solid medium having high adsorptive capacity. A
large surface area or large micro-pore volume can be
achieved due to the porous structure of the solid. The
success of the adsorption process depends on the per-
formance of adsorbents in both equilibria and kinetics. A
solid exhibiting favourable adsorption isotherm as well
as faster kinetics is supposed to be a good adsorbent.
Therefore, in order to be a good adsorbent, a solid must
have 1) a reasonably larger surface area, and 2) a rela-
tively larger pore network for the transport of molecules
to the interior. A relatively larger breakthrough time and
gradual increase in the concentration following break-

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review 30
through are desirable. Recently there have been a series
of studies in this area focusing on:
 Theoretically establishing condensation followed
by adsorption to be more effective in controlling
VOCs than the condensation or adsorption alone, if
the VOC concentrations varied over a large range
[37].
 Experimental analysis to confirm adsorption is an
effective means for controlling VOC if the concen-
tration levels are typically lower than 1%, which is
mostly the case with air bound VOCs in parts per
million (ppm) level, while the condensation is
suited for higher concentration levels [38].
 Experimentally demonstrating the suitability of ac-
tivated carbon fiber in effectively adsorbing VOCs
from inert gaseous stream under varying operating
conditions [39,40].
Although there are commercially available adsorbents
such as granular activated carbon (GAC), silica gel and
zeolites, the search for material with greater adsorption
potential and effective regeneration allows investigation
on activated carbon fiber–toluene combination to judge.
Certain successful mathematical model has also been
derived to predict breakthrough characteristics taking
into account gas-particle film mass transfer resistance,
adsorbent pore diffusion and the adsorption/desorption
rates (proved to be sole determinant of the dynamics)
within the pore under dynamic conditions of different
temperature (35 - 1000˚C), gas concentration (2000 -
10,000 ppm), gas flow rate (0.2 - 1.0 slpm) and weight of
the adsorbent (2 - 10 g). A bed temperature of 50˚C was
found to be favorable for both toluene and m-xylene,
although a relatively larger adsorption of m-xylene by
ACF was indicated. A temperature of 150˚C and regen-
eration time of 60 - 75 min were typically required for
the complete regeneration of ACF and even after 25-30
times of adsorption/desorption cycles no appreciable loss
in its adsorption capacity was evident in the correspond-
ing breakthrough response.
This kind of air stripping and adsorption are estab-
lished processes but these suffer from the disadvantage
of pollutant transfer to the second phase. The expensive
air stripping process is applied to compounds having
significant higher partition coefficient to air over water.
Activated carbon adsorption is not effective economi-
cally as the spent carbon has to be regenerated time to
time or disposed off and disposing of spent carbon
should be done in environmentally accepted manner.
7.2. Pervaporation of VOC in Aqueous Medium
Pervaporation (PV) is a membrane process involving
separation of liquid mixtures through a dense membrane.
In PV, separation of the desired component is achieved
by its preferential sorption and diffusion through the
membrane under reduced pressure which creates a
chemical potential gradient in the liquid phase. The se-
lectivity of the membrane is the determining factor in the
relative flow of the different components. The cost of PV
increases linearly with increasing system size, which
makes PV most competitive for small to medium-sized
stream for removal of VOCs. Since the selective permea-
tion and diffusion of the VOCs through the membrane
are dependent on their interaction with the membrane
material, their sorption and diffusion behaviors through
the membrane are functions of solubility parameter
(thereby interaction parameter of the membrane poly-
mers with the VOCs), chain rigidity or Tg of various
components of membrane, hard segment concentration,
presence of plasticizers and crosslink density in case of
network polymer. Experimental parameters like feed
temperature and concentration also have effects on sepa-
ration performances like flux and separation factor.
 It appears from the chemical nature of chlorinated
VOCs that a membrane with both flexible non-polar
and rigid polar organic domains would be more
suitable for their separation [41]. Segmented poly-
urethanes with elastomeric soft domain and rigid
urethane as well as urea domain can be projected as
an ideal material of such type. A novel crosslinked
hydroxyterminated polybutadiene based (HTPB)
polyurethane urea (PUU)–poly (methyl methacry-
late) (PMMA) interpenetrating network (IPN)
membrane has been developed, which shows due to
comparable solubility parameter values more affin-
ity of VOC molecules to the PMMA moiety was
evident and thereby with increase in polar PMMA
separation efficiency also increases. Decrease in
NCO/OH ratio (decrease in hard segment content)
decreases crosslink density and subsequently re-
sults in increased sorption. With increase in the
feed concentration flux of chlorinated organic com-
pounds increases. As the VOC concentration in the
feed is increased, the membrane is more swollen
due to polymer chain flexibility and increased in-
teraction with PMMA component. All the mem-
brane compositions show flux and selectiveness in
the order of 1, 1, 2, 2-tetrachloroethane < carbon
tetrachloride < chloroform < trichloroethylene.
 Pervaporation membranes have been made from
some homopolymers like unplasticized polyvinyl
chloride (UPVC), plasticized PVC (PPVC), poly-
styrene (PSTY) and blends of UPVC and PSTY in
different compositions to assess sorption and per-
vaporation of tetrahydrofuran (THF) with different
concentrations (0.44–11.3 wt.%) in water under
various conditions like feed concentration, tem-

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review31
perature etc [42]. The higher concentration of THF
in feed promotes greater extent of sorption by
swelling the THF selective membrane, whereas
sorption selectivity decreases exponentially with
feed concentration with PSTY, due to its highest
hydrophobicity among all other types of mem-
branes absorbs minimum amount of water, per-
forming best. The activation energy for sorption
and permeation was found to decrease linearly with
increase in feed concentration of THF. For all the
membranes separation characteristic decreases with
increase in temperature. This may be due to in-
creased permeation of both water and THF at
higher temperature. The presence of polar dioctyl
phthalate (DOP) plasticizer has caused maximum
sorption by softening the stiff UPVC matrix by in-
creasing its free volume. The higher sorption of
UPVC than that of PSTY may be ascribed to its
closer solubility parameter value with respect to
THF.
The attractiveness of the process is that the polluting
compounds are selectively removed from the feed in al-
most pure form.
7.3. Biodegradation of VOC in Aqueous Medium
Aerobic biological processes such as the activated sludge
process are very effective in removing volatile organic
compounds from wastewaters. To come out with a bal-
ance between too high concentration of hazardous waste
causing inhibition of microorganism and too low rate of
addition heading towards starvation of microbial cell,
two phase partitioning bioreactor (TPPB) using water
immiscible and biocompatible organic solvent has been
well studied by a series of experiments by D. Singh et al.
In TPPB 5000 mg/l benzene was biodegraded up to
50.17% over a period of 168h [43,44].
But VOCs like tetrachloroethylene, which are found to
be resistant to biodegradation under aerobic conditions,
can be successfully treated using upflow anaerobic
sludge blanket (UASB) reactor [45,46]. The study was
undergone to develop granular sludge using municipal
digester sludge in the presence of tetrachloroethylene
(PCE) by investigating the effect of increased concentra-
tion of PCE on operational parameters of UASB reactor
to dechlorinate PCE, and the effect of hydraulic retention
time (HRT) on the performance of the process and to
determine the kinetic parameters for the dehalogenation
of PCE in a UASB reactor fed with a synthetic wastewa-
ter. The granules of 0.25 ± 4 mm size were observed af-
ter 82 days having mostly Methanothrix and Methano-
sarcina bacteria. Influent PCE concentration of 5-50 mg/l
decreased to less than 0.23 mg/l (98.5% ± 1% removal)
in most cases. The trichloroethylene (TCE), cis-1,2-di-
chloroethylene (cis-DCE), vinyl chloride (VC) and eth-
ylene were formed on dehalogenation of PCE. Under
steady state operation conditions the COD removal of
94% ± 2% and biogas production of 0.559 ± 0.508 m3/kg
CODrem with methane content of 64% ± 2% was
achieved. The maximum PCE dechlorination rate (qmax)
was 14.28 mg PCE/g VSS.d and the half velocity coeffi-
cient, (Ks), was 0.417 mg PCE/l under steady state con-
ditions. The granules acclimated to PCE exhibits better
removal capability to the higher concentration of PCE.
Biological treatment being a slow process is not very
effective.
7.4. Biofilters
Cost competitive and efficient biofilters require very lit-
tle supplementary nutrients for enhancing microbial sus-
tainability and do not produce any hazardous secondary
pollutants. Different filter bed-nutrient combinations are
in use for treating VOCs experimentally. Table 3 gives a
comprehensive idea about the different experimental
studies in this field.
Biofilter media are not effective at high temperature
due to omission of microbial community.
7.5. Catalytic Combustion
Oxidative destruction is possible at low temperature in
presence of a catalyst and this energy efficient process
can operate with very dilute pollutants [51]. Manganese
nodule and TiO2-SiO2 have been studied for decomposi-
tion of VOCs [52,53]. High temperature stable iron and
manganese mixed pillared clay having high manganese
content shows acetone decomposition reaction whereas
material with high iron contents acts as a better catalyst
for trichloroethylene decomposition [51].
7.6. VOC Free Product Development
Except for the previously mentioned approach of de-
struction of VOC in some media (air or water), there is a
completely separate view to design low or zero emission
product in place of common VOC emitting items. A bio-
degradable, eco-friendly vegetable oil based ink which,
unlike conventional lithographic ink, doesn’t contain
aliphatic solvents and also doesn’t use aliphatic and aro-
matic solvents for cleaning various surfaces, which are
coated with the ink, is prepared and characterized by
Maji C. et al. [54,55]. The oil is a drying oil, a natural
product containing triglycerides of fatty acids with un-
saturated double bonds. These triglycerides react in the
presence of light with oxygen in the air to crosslink,
making the ink permanent on paper. The alkyd resin is
non-volatile, synthetic, low molecular weight polyester
with pendant aliphatic and carboxylic acid groups. It is
similar to the resins made for use in paints. In its acid

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review 32
Table 3. Different biofilters used for removal of VOCs.
VOC used Filter Composition Input parameter Performance Observations
Elimination capacity for
Toluene 24.33-29.13 g/m3h
Elimination capacity for
Xylene 8.784-19.087 g/m3h,
Removal efficiency 82%
BTX [42]
PVC spheroids as packing
material, concentrated
sludge from municipal
sewage along with a
previously toluene
acclimatized microbial
culture
loading rate: 0.55 g/m3,
Empty bed residence
time (EBRT)72 s
Elimination capacity for
Benzene 5.928-24.4 g/m3h,
Removal efficiency 86%
Xylene appears to be more
toxic than benzene and toluene.
The system recovers original
efficiency quiet fast even after
a prolonged shock loading.
Inlet concentration of
Toluene: < 0.5 g/m3
EBRT 2.45 min
Removal efficiency > 90%
Toluene, Indus-
trial emission
mixture of Tolu-
ene and Benzene
[47]
Compost based biofilter
unit inoculated with a
mixed microbial population Inlet load of Toluene
263 g/m3h
Elimination capacity 128
g/m3h
Biomass concentration doesn’t
affect removal efficiency.
In the up flow biofilter removal
is more efficient in the lower
part.
Inlet loading 300 g/m3h,
flow rate 0.18 m3/h Removal efficiency 90%
Toluene [48]
Agro waste-Yellow-gram
(Cajanus cajan) stalk
inoculated with a mixed
culture Inlet loading 328 g/m3h,
flow rate 0.24 m3/h Removal efficiency 88%
Elimination capacity increases
with initial load in the mass
transfer controlling zone, and
then attained a constant value
in reaction controlled zone.
Removal efficiency is constant
at mass transfer zone, and then
decreases with increase with
initial load in reaction
controlled zone.
Mono-chlorobenz
ene [49]
Trickle bed air filter made
up of coal packing material
inoculated with mixed
consortium of activated
sludge obtained from
sewage treatment plant
Concentration < 1.069
g/m3, EBRT < 94.26 s Removal efficiency > 90%
Overcomes the starvation
within 3 days of re-acclimation
time
BTEX [50]
Microbial acclimatized
mixture of compost, sugar
cane bagasse and
granulated activated carbon
(GAC) in the ratio 55:30:15
by weight
Inlet load 126.5 g/m3h Elimination capacity 83.65
g/m3h
Increase in the CO2 production
with elimination capacity
increases the removal of BTEX
could mainly due to the growth
of microorganism.
form, it is hydrophobic. As a sodium salt, however, it is
sufficiently hydrophilic to act as an emulsifier. Thus,
during printing, the resin is hydrophobic, but during
clean-up, it makes the ink emulsifiable in the mildly al-
kaline aqueous wash solution. The presses are cleaned by
washing with water at slightly elevated pH and thereby
no waste-water threat of a secondary pollution during
washing of presses. The success is not only its strong
performance in printing, but also its kinetics of washing.
The later is quantified by measuring the rate of neutrali-
zation of the wash solution and thereby obtaining the
mass-transfer coefficient as dependent on process vari-
ables like diffusion coefficients, stirring rates, interfacial
areas, and concentrations. Acid-base kinetics is very fast
and the rates are expected to be independent of the
acid–base constants.
8. Conclusion and Future Scope
From the current discussion the major issues regarding
VOCs in India include, among the anthropogenic sources,
transportation and biomass burning. NMHCs cause the
production of tropospheric ozone in the presence of suf-
ficient amount of NO in the atmosphere and higher mo-
lecular weight of the hydrocarbon species results in more
reactivity in ozone production [1]. This is the common
scenario in all four metro cities like Delhi, Mumbai,
Chennai and Kolkata [57]. Thereby, the growth in terms
of industrialization and urbanization should be attained
with proper precaution in traffic and fuel related conse-
quences.
 It has been well established that with regular main-
tenance and upgradation of engine and fuel tech-

Ambient Air Non-Methane Volatile Organic Compound (NMVOC) Study Initiatives in India - a Review33
nology exhaustive emission from vehicular fleet
can be controlled. Emissions from tyres also
needed attention as improving the quality of tyre
can cause less contribution in contamination of
ambient air because of its VOC content [57]. In
addition to rubber compounds, Carbon black (rein-
forcing fillers), Textile and Steel fibres in form of
cord/rayon, synthetic suite of nylons and polyes-
ters(reinforcing fibers), Petroleum oil, naphthenic
oil or aromatic oil (lubricants),vulcanizing agents
like organo sulfur compounds, Zinc oxide and
Steric acid as curing agent are used in manufactur-
ing tyre. In a comparative study including emis-
sions of VOCs from wear and tear of automotive
and aeroplane tyres by Patil S. et al. It was depicted
that as many as sixty-six VOCs including twelve
HAPs were identified among which fifty one
VOCs were associated with automobile tyre. Aero-
plane tyres not only generate lesser numbers of
VOCs, but the concentrations generated are also
comparatively small. Retreading and burning of
tyres are very common in Indian cities and thus
should be considered as a major source of air pol-
lution. Since fuel adulteration also has come up as
possible source, restrictions should be imposed on
that kind of malpractice.
 On Governmental basis, certain steps and targets
are established like, use of CNG in place of petrol
or use of four stroke low emissive engine replacing
two stroke ones; proper regulatory monitoring
should be continued to assess the change in VOC
level or shift in source profile. Unless it is helping
in ambient air quality in Indian condition, no meas-
ure just for the sake of changing the technology
would do any good to the current situation.
 Although it should be kept in mind that, consider-
ing factors including economic and technical feasi-
bility, regulatory standards are 15-min, 1-hr 8-hr
based, but an exposure level lower than the rec-
ommended standard does not mean that a life-long
exposure at such a level is safe; In addition, most
of the standards were not established based on
NOAELs (No observed adverse effect levels) or
LOAELs (lowest observed adverse effect levels);
still some restrictions should be imposed with strict
laws which may need to be modified based on new
discoveries or new economic and technical feasi-
bilities. This should be accompanied with public
awareness so that following or maintaining the
standards do not become a burden, rather than a
responsibility for the common people.
 Considering different aspects of research going on
in India based on VOCs, some important studies
are really lacking and can be taken for serious as-
sessment.
 From certain source apportions the dumping sites
have been considered possible basis of certain
VOCs, but thorough study on this subject has not
been recorded till now. Thereby the release of VOC
in current scenario and corresponding change in
case of applying certain technologies like utiliza-
tion of solid waste as fuel and organic manure
should be monitored in long term surveys.
 There is natural inclination towards biofuel
throughout the world keeping in mind the dimin-
ishing volume of fossil fuel. In India the effect on
VOC profile with introduction of biofuel should be
undertaken although the socio-economic impact
should also be taken into account.
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