Seasonal Influence in Traffic-Related Air Pollutants Concentrations in Urban Parks from Porto Alegre, Brazil

Traffic-related air pollution is an alarming source of pollutants exposure and consequently to the development of several adverse health effects. Otherwise, green spaces are reported to improve health status. Although, in an urban scenario most of these areas are located near air pollutants sources, as vehicle fleet. Thus, the aim of the present study was to determine, during one year, the levels of nitrogen dioxide (NO 2 ) and ozone (O 3 ) in the main parks from Porto Alegre—Brazil. This study focused on three urban parks: Germânia, Moinhos de Vento and Marinha do Brasil Park. Nitrogen dioxide and ozone measurements were accessed by passive monitoring in four campaigns in-cluding all seasons and performed at distances of 0 m, 15 m, 30 m, 45 m, 60 m and 75 m from the main road at each park. NO 2 and O 3 concentration among the parks was not different (p > 0.05), as well as the mean concentration of NO 2 and O 3 of all parks in the six sites did not differ (p > 0.05). However, season 1 and 3 showed increased NO 2 and O 3 concentration. Temperature were decreased in season 1 and 3 (p < 0.05), while humidity, pressure and insolation showed no difference among seasons (p > 0.05). Traffic flow was higher in Moinhos de Vento Park and Marinha do Brasil Park compared to Germânia Park (p < 0.05). Overall, the seasonal variation could directly interfere in NO 2 and O 3 concentration in urban parks from Porto Alegre.

modern metropolises, the requirement of a huge amount of environmental resources occurs mainly due to the accelerated expansion of the economy and population growing [1] [2]. The exposure to a polluted atmosphere may result in damage to our environment and potential health risk to humans. Reports demonstrated that every year outdoor air pollution is responsible for 4.2 million deaths around the world, while indoor air pollution for 3.8 million deaths [3]. Exposure to air pollutants as nitrogen dioxide (NO 2 ) and ozone (O 3 ) has been correlated with increase in mortality and hospital admissions caused by respiratory and cardiovascular diseases. These outcomes have been found both in short and long-term studies [4] [5] [6] [7].
Our society still relies heavily on fossil fuels for various purposes, such as transportation, due to this, traffic-related air pollution is an alarming source of human exposure to air pollutants [2] [8]. Many health studies have connected adverse health effects with spending significant amounts of time near high-traffic roads with elevated air pollution levels [9] [10] [11] [12]. Otherwise, green spaces are reported to improve health status once people use public areas to perform physical activity and have a leisure time, which serves as a key strategy to maintain and improve population health [13]. Although, in an urban scenario, most of these areas are located near air pollutants sources, as vehicle fleet [14]. Some researchers have alert that health risks from exposure to air contaminants may increase during exercise because ambient air pollutants affect health and exercise may amplify the respiratory uptake and deposition of air pollutants in the lungs [15]- [20].
Trees and other vegetation reduce air pollution levels through the interception of airborne particles or through the uptake of gaseous air pollution through leaf stomata on the plant surface [21] [22] [23] [24]. On the other hand, Nowak and colleagues (2010) showed that removed pollution particles can be re-suspended to the atmosphere during turbulent winds, negatively impacting local air. Besides that, high vegetation can reduce mixing and turbulence resulting in increased pollutants concentration levels [25]. This can be explained by the fact that trees and other types of vegetation reduce the ventilation that is responsible for diluting the traffic emitted pollutants. Several studies demonstrated that green spaces located in urban street canyons can obstruct the wind flow thereby reducing the ventilation leading to higher pollutant concentrations [26] [27].
In view of the indisputable health benefits of exercising and having leisure times together with the little amount of knowledge about the levels of air pollution at public urban parks it is important to know the concentration of pollutants gases and understand the factors that affects it. So, the aim of the present study was to determine, during one year, the levels of NO 2 and O 3 in the main parks from Porto Alegre-Brazil.

Study Area
The study was conducted in the city of Porto Alegre (30˚01'59"S, 51˚13'47"W), Open Journal of Air Pollution which is the principal city from the state of Rio Grande do Sul, located in the Southern Brazil. This city has approximately 1.409 million inhabitants (2.83 people per km 2 ) and the climate is considered humid-subtropical, with aboveaverage precipitation throughout the year.
This study focused on three representative urban parks that were chosen for field experiments: Germânia Park, situated at Túlio de Rose avenue (30.

Air Pollutants and Meteorological Parameters
The four sampling campaigns (September/2017 = season 1; January/2018 = season 2; June/2018 = season 3; September/2018 = season 4) were chosen to examine pollutant patterns over more than one season, to ensure that our findings were robust over time. In each campaign vehicular traffic was recorded and blind analyses of vehicular flow was performed by two observers. Climatic variables (air temperature, relative humidity, pressure, wind direction and insolation) were obtained from INMET (National Institute of Meteorology) recorded at José Luiz Carneiro Cruz public square (Porto Alegre, Brazil).
In this study, cellulose filters (37 mm, Energética, Rio de Janeiro, Brazil) were used as a diffusive surface into a sampler which was placed in trees at a height of 2 meters, as illustrated in Figure

Statistical Analysis
Statistical analysis was carried out using SigmaPlot version 12.0 for Windows (Systat Software, Inc.) and GraphPad Prism version 6.0 for Windows (Prism 6; Open Journal of Air Pollution GraphPad Software, Inc.). Study variables were tested for normality using Shapiro-Wilk or Kolmogorov-Smirnov test. To analyze parks and sites variables we used one-way ANOVA, followed by Tukey's post hoc test. The interaction between parks and seasons were obtained by two-way ANOVA, followed by Tukey's post hoc test. Values were reported as mean ± standard deviation. A p < 0.05 was considered statistically significant.

Results
In the present study, NO 2 concentration among the parks was not different (p = 0.447) (Figure 3(a)). The NO 2 concentration average of all parks in the six sites did not differ among them (p = 0.993) (Figure 3(b)). In season 1, NO 2 concentration were increased when compared to season 2 (p = 0.007). Also, it was observed an increase of NO 2 concentration in season 3 when compared to seasons 1 (p = 0.048), 2 (p < 0.001), and 4 (p < 0.001) (Figure 3(c)). While, when the interaction of seasons with the parks was compared, it was observed an increase of NO 2 concentration in season 1 compared to season 2 (p = 0.005) and in season 3 compared to seasons 1 (p = 0.0449), 2 (p < 0.001), and 4 (p < 0.001) in all parks (Figure 3(d)). Regarding O 3 concentrations, a difference among the parks was not observed (p = 0.670) (Figure 4(a)). Also, the O 3 concentrations among the six sites of the parks were not different (p = 0.898) (Figure 4(b)). O 3 concentrations in seasons demonstrated an increase in season 1 and 3 compared to season 2 (p < 0.001) and 4 (p < 0.001), and augment in season 2 when compared to season 4 (p = 0.025) (Figure 4(c)). In addition, the O 3 concentration in Germânia Park was increased in seasons 1 and 3 when compared to seasons 2 (p < 0.001) and 4 (p < 0.001). In Moinhos de Vento Park, the O 3 concentration was increased in season 1, 2 and 3 compared to season 4 (p < 0.001). In Marinha do Brasil Park, the O 3 concentration was increased in season 1 when compared to season 2 (p = 0.030) and 4 (p < 0.001), and season 3 compared to season 1 (p < 0.001), 2 (p < 0.001) and 4 (p < 0.001). Marinha do Brasil Park showed increased O 3 concentration in season 3 when compared to all seasons in Germânia (p < 0.001) and Moinhos de Vento (p < 0.001) parks (Figure 4(d)).
The meteorological measures of the seasons showed that season 1 and 3 had decrease temperatures compared to seasons 2 and 4 (p < 0.05). Humidity, pressure and insolation showed no difference among seasons ( Figure 5). When assessed

Discussion
The results of this study showed a seasonal variation of pollutants concentrations among urban parks, demonstrating that mainly season 1 and 3 had higher concentrations of NO 2 and O 3 . The unique meteorological measure that may potentially interfere in this variation is temperature. So, in the seasons with lower temperature, an increase on traffic-related air pollution concentration was detected. Furthermore, there was no difference among parks concentration of  (1 and 3). In contribution to our result, cold seasons are associated with high pollution episodes, being the highest levels of pollutants occurring in winter [30] [31] [32] [33]. During low temperature and winter days, thermal inversion is commonly observed, and, in this period, the concentration of pollutants tends to be higher, leading to a poor air quality environment [34]. Also, parks could intensify low temperature and contribute to pollution concentration due to the shading and cooling effect caused by trees that act as barrier of pollutants [35] [36]. Our study had a limitation that must be considered. We did not measure additional pollutants released from vehicular emissions, such as MP2.5 and SO 2 .
The levels of these pollutants associated with NO 2 and O 3 concentration could provide a more complex panorama to our study and a better understanding of our results.

Conclusion
Thus far, the seasonal variation could directly interfere in NO 2 and O 3 concentration in urban parks from Porto Alegre. It indicates that cold seasons contribute to the deterioration of air quality. The sites of the parks seem not to interfere in the local air quality, since a gradient of pollutants concentration was not observed.