Influence of Meteorology on Particulate Matter ( PM ) and Vice-Versa over Two Indian Metropolitan Cities

This present study addresses the relationship between Particulate Matter (PM) and meteorological parameters over two metropolitan cities in India (Delhi and Pune) together with the Potential sources contribution function (PSCF) in order to understand the role of the transport on the variability of PM for a period of one year. To examine the variations of PM, over different time scales (diurnal and seasonal), at different observational locations, diurnal scales, are shown that maximum values of standard deviations (SD) are found in early hours of morning around 10AM, and later hours in the night over Delhi, however, the maximum values of SD are found in the morning hours around 8 to 10 AM over Pune. The relationship between PM and meteorological parameters is studied and explains a positive relationship between wind speed and planetary boundary layer height (PBLH), with a PM. Also, analyses on the Potential source contributions function (PSCF) over Delhi show that higher source contributions are observed during months of November, December and January over the region of Indo Gangetic Plain (IGP) plane north and Eastward of Delhi. Similarly, over Pune, most of the time, the source contribution in terms of pollution in Pune is coming from the south-east and eastern part of India, except in the winter season in the months of (December, January, and February). This analysis clearly suggests that the orography is played a pivotal role over the variations of PM over Pune.


Introduction
Over last several decades, environmental chemistry and climate are major issues due to the drastic change in the levels of particulate matters (PM) and gaseous components in the metropolitan cities of all over the world [1] [2].PM is a heterogeneous and complex mixture of liquid and solid particle in the ambient air having different sizes like fine (PM 2.5 ) and coarse (PM 10 ) particles and their concentration influences air quality over urban areas.Their concentration also plays an important role in the atmosphere such as radiation budget, cloud, and precipitation formation, visibility, etc. [3] [4].Additionally, PM affects the climate indirectly by acting as cloud condensation nuclei and thereby affecting cloud microphysical and radiative properties [5] [6].Ambient particles with aerodynamic diameters < 2.5 μm (PM 2.5 ) are mainly responsible to the health hazards and earth radiation budget while PM 10 (aerodynamic diameters < 10 μm) is mainly accountable to the visibility [7].PM 2.5 has been directly linked to various health issues leading to mortality and morbidity [8] [9] [10] [11] and other environmental concerns [12].Based on the World Health Organization-WHO (2002) report, 800,000 deaths (1.4% of the global population) can be attributed to urban air pollution.The growth of cities in developing countries is the strongest affected by urban air pollution showing the highest burden of diseases including increased mortality [13] [14].PMs are released into the atmosphere due to the anthropogenic and natural activities; high PM loads in the urban areas are produced by local activities [15].The major sources of PMs are incomplete combustion of fossil fuels, mixed industrials emissions, especially coal, diesel, use of bio-fuel in cooking stoves, municipal waste burning, crop residue, and brick kilns activities.In addition to this, PM 10 emits in the air from the construction activities, paved and unpaved road, and also dust storm activities.Weather parameters are major components which play a dominant role in distribution of ambient pollutants in the atmosphere and also it varies from day to day, location to location and season to season.For example, Wind Speed (WS) and direction are considered to be the important meteorological variables that play a vital role in the distribution of pollutants [16] [17].In addition to local activities and meteorological conditions, the transport of air parcels from the distinct regions is one of the factors leading to the concentrations of PMs at the site [18] [19].To understand the PMs characteristics and their emission signature, many studies have been carried out across the world [20] [21] [22].Limited studies have been done over India region such as [23] in Ahmadabad, [23] in Chennai [17] [24], Udaipur [25], in Pune [26] and [27] in Delhi.Detailed investigations of PM 2.5 and PM 10 with weather parameters are still limited in India.Continuous measurements of PMs along with meteorological parameters were used to understand the pollution load, seasonal variability, climatology, and the source of apportionment and trajectory pathway of these air pollutants over Delhi and Pune.Back trajectory calculations were also performed to study the effects due to meteorology.

Topography and General Meteorology
Delhi is located at (28.37˚N; 77.12˚E, 216 m above mean sea level-MSL) and covers ~1500 km 2 of the industrial area including the suburban towns of Ghaziabad, Noida Faridabad, and Gurgaon.According to 2011 census, Delhi is the second highest populous (~11 million population) city in India, as well as it is one of the most polluted urban environments over the globe.Delhi climate is humid subtropical climate and hot semi-arid with high temperatures of 40˚C -45˚C in pre-monsoon (warm) season while lowest of 13˚C -15˚C during in winter period.The monsoon arrives at the end of June, along with an increase in humidity.
Pune is located at (18.5˚N; 73.8˚E) an altitude of about 550 m above the MSLs, it is situated in the western zone of the Deccan plateau and covers an area of ~700 km 2 .It is one of the most rapidly developing cities in India in terms of industries as well as vehicular population and also urbanization [28].Pune has a tropical wet and dry climate with average temperatures ranging between 20 to 33˚C [29].Number of vehicles over Delhi and Pune are increasing 2 to 3 times [29] [30] within a decade.By the year 2010, the vehicular count for Delhi is 57 lakh's and over Pune, 1000 vehicles per hour cross the signal [29].The monitoring stations are placed at strategically selected locations by including different sectors with vehicular transport, industrial pollution, biomass burning, residential etc.More detailed information about the instrumentation, quality control of the data from the SAFAR network at different observational locations over Delhi and Pune (http://safar.tropmet.res.in/) are reported in [24].

Experimental Techniques
Continuous measurements of PM 2.5 and PM 10 with meteorological parameters were carried out from the System of Air Quality Forecasting and Research (SAFAR) network of the year of January-December, 2015.It consists of eight Air Quality Monitoring Stations (AQMS) and Automatic Weather Stations (AWS) set up across Delhi and Pune.PM 2.5 and PM 10 mass concentrations were observed using the Beta Attenuation Monitor (BAM-1020; Met One Instruments, Inc., USA).The BAM-1020 measures the mass concentrations of airborne particulate matters in (µg/m 3 ) using the principle of beta ray attenuation.A small Carbon-14 (14 C ) element provides a constant source of high energy electrons known as beta rays.The beta particles are detected and counted by a sensitive scintillation counter.Detailed information of BAM-1020 has been reported in a study by [19].AWS was continuously operated and measures meteorological parameters, viz.wind speed, wind direction, temperature, relative humidity, etc., during the study period and the data were recorded at every 5 min interval and then binned at the one-hour interval after a quality check for further analysis and comparisons [31].Planetary boundary layer height (PBLH) is taken from ERA-Interim reanalysis data.

Methodology
Potential Source Contributory Function of PM2.5 The potential source contribution function (PSCF) is used to calculate the possible source locations using back trajectories [32].The air mass back trajectories for Delhi and Pune during the year 2015 were calculated using the Hybrid Single-Particle Lagrangian Integrated Trajectory-4 (HYSPLIT-4) and are shown in Figure 7 and Figure 8 respectively.The back trajectories started from each 00:00 (UTC) on every month of the year 2015 at 100 m, which represent air masses from low altitudes.We calculated five days (120-h) back trajectories at 24 hourly based on HYSPLIT using National Centers for Environmental Prediction (NCEP) reanalysis data with a gridded resolution of 1˚ × 1˚.The arrival heights of the trajectories were at the surface (100 m).To calculate the PSCF, the geographic region covered by the trajectories was divided into an array of 0.3˚ × 0.3˚ grid cells with surface height and the PM 2.5 concentration kept within a threshold limit 95%.

Annual Distribution of PM10 & PM2.5 over Delhi and Pune
The analysis was begun from the annual variations of PM at all the observational locations over Delhi and Pune.The higher values of PM 10 were observed over Delhi as compared to Pune (it was the same case for PM 2.5 ).All the stations over Delhi were having the same amount of PM in all the seasons with the higher values are found during the pre and post monsoon seasons, and the lower values are observed during the monsoon months due to the settling of pollutants by rainout and washout mechanism.And the same is the case for Pune with the higher values were found during the pre-monsoon and the lower is observed during the summer monsoon season (Figure 1).The annual mean mass concentration of PM 2.5 and PM 10 over Delhi were in the ranges of 27 -796 μg/m 3 and 9 -600 (μg/m 3 ), respectively.However, in Pune PM 2.5 and PM 10 were found in the ranges of 3 -428 (μg/m 3 ) and 1 -180 (μg/m 3 ), respectively in the year 2015.
The annual mean concentrations (±standard deviations) of PM 2.5 and PM 10 for all air quality stations for Delhi and Pune are shown in Table 1 and Table 2 [4].Figure 1 shows that the particulate matter levels are higher in the November and December followed by the May months over the Delhi, we can observe in the Pune the PM concentration is high during November and December followed by the April month.

Diurnal Variations in PM10 and PM2.5
The average diurnal variations in PM 10 , PM 2.5 and their ratio concentration at The variability over different locations over Delhi found to be higher in terms of their SD than the locations over Pune (Figure 2).The maximum values of SD

Role of Meteorology
Ambient conditions of air pollution distribution will mainly depend on local meteorological conditions as well as long-range transport; Strong seasonality will lead to modulating the air quality levels [17] [27].The seasonal distributions of ambient pollutants such as PM 2.5 and PM 10 are controlled by the emission sources, topography, local meteorology, transport factors and boundary layer height in the tropical atmosphere [19].It is already well established that the meteorology will identify the transport and diffusion of the air pollution cycle, Meteorological factors such as winds direction, wind speed, temperature, precipitation, atmospheric boundary layer, relative humidity play an important role to determine the air pollution levels [33].Impact of all these meteorological parameters in PM concentrations is significantly important and variability depends on the season or specific meteorological and atmospheric regimes dominated on certain days [34].On the other hand, it is impossible to determine the influence of any individual meteorological parameter on PM concentrations with high accuracy due to contradictory and multiple effects that they may have on accumulation and dispersion of pollutants.

Meteorology Influences on PM over Metro and Metropolitan City
Time series of particulate pollutants and meteorological variables are shown in [33] [35].Figure 4 shows the relationship between the PM and various meteorological parameters over Delhi.In Figure 4  In Figure 4(b), its looks a negative relationship between RH and PM, when there are higher values especially during the monsoon.[33] Shows a similar kind of study show similar results over Delhi, PM is shown lesser.[18] Described the relation of RH and radiative properties of aerosols.[38] Has showed that the higher relative humidity and lower temperature during monsoon period at Pune caused the growth of cloud droplets which resulted in higher rainfall.Interestingly, a positive relationship has been found between wind speed and PM.It indicates that when there is higher value of winds causes the higher values of PM which is obvious reasons for a positive relationship.The same relationship also was observed for the planetary boundary height (PBLH).
On the other hand, the relationship between PM and meteorological parameters were further analyzed, as shown in Figure 5 over Pune. Figure 5(a), there are higher values observed during pre-monsoon and monsoon period in temperatures, but in case of PM, higher values only were observed during the pre-monsoon period.In case relative humidity throughout the year over Pune except during the pre-monsoon season, however, the minimum values of PM over Pune is also observed during the monsoon as like Delhi due to rainout/washout mechanism.However, a negative relationship is observed between wind speed and PM values especially during monsoon season, which is opposite to Delhi in Figure 5(c).One can clearly see there is a positive relationship between PBLH and PM over Pune.These relationships will provide with the dis-tinct meteorological systems which control the variability in different seasons over both metropolitan cities.
Further, in order to see the contribution from both PM 10 and PM 2.5 , we have shown the scatter plot in Figure 6.It shows the linear relationship between PM 10 and PM 2.5 , these parameters show higher positive correlations of about 0.94 (0.91) over Delhi (Pune).This analysis clearly indicates that these higher values of CC associated with the PM 2.5 contribution in the particulate matter which causes the pollution over both the cities.

Potential Source Contributions and Source Apportionment
Long-range transport of particulate matter is important to understand the direct emissions from local sources.Figure 7     a color from blue to red, and highest values of PSFC with a range of (0.5 -0.9) can be observed in the months of January in the north-Eastern parts of Pune.
The lowest PSFC values with a range of (0.1 -0.3) are observed in remaining months which appeared to be cleaner.

Summary and Conclusions
In this study the variability of PM over two metropolitan cities in India was studied using the ground-based observational datasets for the period of one year.In addition to this variability, we have also done the analysis on the source contributory function in order to understand the long-range transport of particulate matter; this will provide the information on the source regions from the emission points.Initially, we begin our analysis on variability by presenting the variations in diurnal and annual means along with their standard deviations.
Analysis indicated that the higher values of PM 10 are observed over Delhi as compared to Pune and also it is the same for PM 2. Further, the relationship between the PM and meteorological parameters also were analyzed in order to see the roles on the maximum and minimum concentrations over both metropolitan cities.A positive relationship has been found t between wind speed and PM.It indicates that when there is a higher value of winds causes the higher values of PM which is obvious reasons for a positive relationship and it is the same relationship for the case also for the planetary boundary layer height (PBLH).But it is interesting to note that there is a negative relationship is observed between wind speed and PM values especially during monsoon season over Pune, which is opposite to Delhi.This analysis will provide with the distinct meteorological systems which control the variability in different seasons at different time scales over both metropolitan cities.
In addition to above analysis, in order to see the long-range transport, i the Potential source contributions function (PSCF) over both metropolitan cities also were analyzed.Higher source contributions were observed during the November, December, and January over the region of IGP plane north and Eastward of Delhi.This is mainly attributed to the heavy dust loading in the pre-monsoon months and stagnant of winds in the winter months the pollution accumulates in Delhi.The lowest values of PSCF within range of 0.1-0.3 is observed in remaining all the months which appeared to be cleaner.On the other hand, over Pune, most of the time the source contribution in terms of pollution in Pune was coming from the south-east and Eastern part of India, except in the winter season in the months of (December, January, and February).Due to fact that the large temperature contrast, there are processes viz., land and sea breeze circulation over the Indian region and southern Indian Ocean, South West winds were carried out from the ocean with the strong winds called jet streams bring the particulate matter pollution toward the western ghats region of India, where Pune is located.This analysis clearly suggests that the orography is also
Pune and Delhi are shown in Figure2.Hourly averaged mean values as well as standard deviations for their variability are presented from the observational locations over both Delhi and Pune.Pronounced diurnal variations of PM are observed in both Metro cities, but with different daily patterns in the two cities.

Figure 4 and Figure 5 .
Figure 4 and Figure 5.It shows annual variations of temperature, wind speed, relative humidity and planetary boundary layer, along with PM 2.5 and PM 10 concentrations on average of all the sites over Delhi and Pune during 2015.The level of PM 10 crosses the threshold level in all months of the year except for the monsoon season (July-October) over Delhi region (Figure4).The ambient air quality standard for PM 10 , set by India is 100 μg/m 3 suggested by the World Health Organization (WHO) guidelines.The mass concentration of PM 10 is found to be maximum during the months of March and December in almost all years[17]
shows a panel plot of monthly PSCF from January to December 2015 at Delhi.Greater PSCF values indicate a higher contribution to PM 2.5 concentration.An area corresponding to a grid of high PSCF value is a potential source region for PM 2.5 concentration, and the trajectory through the region is a path indicating the high PM 2.5 concentration.Most of the time the particle pollution is coming from the north-west and northern parts of India, except in the monsoon season (June, July, August, September) in which the particulate matter pollution is carried from the south-west and Arabian Sea part of India, It is because of carry forward of pollutants with mean winds during the monsoon.The values range from 0-1 showing a color from blue to red, and highest values of PSFC with a range of (0.5 -0.8) can be observed in the months of May in the northward portion of Delhi, as well in November, December and January was observed in the region of IGP plane north and Eastward of Delhi, It is due to the heavy dust loading in the pre-monsoon months and stagnant of winds in the winter months that causes the accumulation of pollutants in Delhi.The lowest PSFC values with a range of (0.1 -0.3) are observed in remaining months which appeared to be cleaner.

Figure 8 Figure 6 .
Figure 8 shows a panel plot of monthly PSCF form Jan-Dec 2015 at Pune, Most of the time the source of pollution in Pune is coming from the south-east and Eastern parts of India, except in the winter season (December, January, and February).Due to large temperature contrast of huge land and sea breeze circulation over the Indian region and the southern Indian Ocean, South West winds

Figure 7 .
Figure 7. Potential source contributory function of PM 2.5 over Delhi.

Figure 8 .
Figure 8. Potential source contributory function of PM 2.5 over Pune.

5 .
Higher values were found during the pre and post monsoon with the lower values during the monsoon months due to settling of pollutants by rainout and washout mechanism at all the stations over Delhi.On the other hand, over Pune, higher concentrations are found during the pre-monsoon and lower values were observed during the summer monsoon season.The analysis is also based on different observational locations over Pune and Delhi by presenting the variations in terms of the means and standard deviations at all the observational locations.Overall analysis of the variations of PM 10 and PM 2.5 over Pune is 2 and 3 times lesser than the Delhi respectively and the annual mean mass concentration of PM 10 and PM 2.5 over Delhi is varied from 27 -796 (μg/m 3 ) and 9 -600 (μg/m 3 ), respectively.However, in Pune PM 2.5 and PM 10 were found in the ranges of 3 -428 (μg/m 3 ) and 1 -180 (μg/m 3 ), respectively in the year 2015.The variations at diurnal scales during the different seasons over both metropolitan cities over India also were studied by using the hourly values.The variability over different locations over Delhi was higher in terms of their SD than the locations over Pune.However, the maximum values of SD have found in the early hours of the morning and later hours in the night over Delhi with also peak in the morning hours around 10 AM, on the other hand, the maximum values of SD are found in the morning hours around 8 to 10 am over different locations over Pune.The reason for the higher concentrations of SD is mainly attributed due to the usage of a high number of vehicles which cause the higher during the observational period.In the diurnal cycle of PM 10 is maximum in the midnight time around 12:00 AM with a value of around 285 μg/m 3 during the winter in Delhi while the minimum is observed around 16:00 PM with a value of 200 μg/m 3 , however, their high deviations are also observed around same time with 115 μg/m 3 while it is the minimum observed as ~65 μg/m 3 .On the other hand, over Pune, it is observed that the maximum (minimum) is around in the morning 10:00 AM (at around 16:00 PM) with a value of about 200 μg/m 3 (90 μg/m 3 ).The Metropolitan cities are showing the strong bimodal pattern which is showing an almost similar pattern.The metro area has a dense traffic and huge pollution will lead to the high concentration of particulate matter as well as low diurnal variation.Enhanced anthropogenic activities are a major source of the higher values in the diurnal.The condition is more or less same for both PM 10 and PM 2.5 with the less SD values over Pune as compared to Delhi.One interesting point here is to notice that the values are lesser in both amplitude and as well as the standard deviations which are almost half of its values over Pune as compared to Delhi.

, re- spectively. Mean values of PM 10 are higher over C.V Raman location with the value
of around 229.15 (μg/m 3 ) while the lower is observed for IMD Aya Nagar in terms of the mean values.While the maximum and minimum values that shown in Table1is over IGI airport is reported as highest among all the stations as 796.67 μg/m 3 whereas the lowest is 38.46 μg/m 3 .Among the other observa-

Table 1 .
Statically values for PM 10 and PM 2.5 for Delhi.

Table 2 .
Statically values for PM 10 and PM 2.5 for Pune.case for PM 2.5 with the higher values of maximum values are recorded over IGI airport and IMD ayanagar with the minimum values of 14.85 (13.65) μg/m 3 with SD of 82.87 (46.30) μg/m 3 for the above two stations.From the statistical calculation, IMD Lodhi road recorded the lower values of both PM 10 and PM 2.5 .Both PM 2.5 and PM 10 concentrations are lower over Pune as compared to Delhi.Within Pune, overall results have shown the higher maximum values over IITM, Pune with Alandi is followed to IITM with the values of 428.04 for IITM and 418.41 μg/m 3 for Alandi.Despite their maximum values, Alandi has shown higher variability of 51.32 μg/m 3 than the IITM with a lesser value of about 34.44 μg/m 3 .Further analysis infers the minimum values over Katraj (Bhosari) as 3.05 (4.34) μg/m 3 with higher SD values 47.10 (58.98).While it is the same case for the PM 2.5 over these locations following the minimum values as 1.34 (1.05) μg/m 3 and higher SD as 28.43 (25.68) μg/m 3 .Over Pune, Nigidi observational locations have recorded the lowest variability in both PM 10 and PM 2.5 among all the other nine stations.However, the overall variations of PM 10 and PM 2.5 over Pune is 2 and 3 times lesser than that of the Delhi respectively, and the annual mean mass concentration of PM 10 and PM 2.5 over Delhi is varied from 27.02 μg/m 3 to 796.67 μg/m 3 and 9.37 μg/m 3 to 600.03 μg/m 3 respectively as well as in Pune the annual mean mass concentration of PM 10 and PM 2.
[30] 5 is varied from 3.05 μg/m 3 to 428.04 μg/m 3 and 1.05 μg/m 3 to 180.81 μg/m 3 as recorded in the year 2015.The observed values of PM 10 and PM 2.5 over Delhi have substantially exceeded the standards of their annual averages with reference to Indian National Ambient Air Quality Standards (NAAQS) i.e. 100 μg/m 3 and 60 μg/m 3 for 24 hours average.But over Pune observed values of PM 10 and PM 2.5 exceeds in win-ter and Pre-monsoon seasons only and rest of the period maintains the standard levels.According to previous studies over Delhi, the transport sector has contributed 45% to total PM 2.5 concentrations, 27% of PM 2.5 is contributed from industrial sector, 24% from industries and 4% from power sector[30]however, and major sources of overall air pollution in Delhi are: emissions from vehicles (67%), coal-based thermal power plants (13%), industrial units (12%) and domestic exhaust (8%)