Current World Environment

Introduction

Clean air is considered to be a basic requirement of human health and for the well-being. However, air pollution continues to pose a significant threat to health worldwide (WHO 2005). The state of air pollution is often expressed as Air Quality (AQ). Air pollution has implications in a number of contemporary issues including: human health, (e.g. respiratory, cancer, allergies.), ecosystems (e.g. crop yields, loss of biodiversity), national heritage (e.g. buildings), and regional climate (aerosol and smog formation) (Monks et al, 2009).

The World Health Organization estimated that 2.4 million people die each year from causes directly attributable to air pollution with 1.5 million of these deaths are only due to indoor air pollution (WHO 2002). In Eastern Canada vehicular emission are the major contributor to Canada’s air where NOx emissions contributes to 8% and 5% contributes to total PM and SOx emissions specially during bad smog days (Environment Canada’s Performance Report 2003). Biomass burning constitutes an important anthropogenic NO_x source in the tropics and subtropics of America, Africa and in South Asia. Due to high population density and higher economical growth rates, emission of these gases are increasing in Asia and more so in central and South Asia (Lelieveld and Crutzen 1994). China is the largest contributor of pollutant among Asian countries where increase in NO_xgrowth rate is found to be about 7% per year (1990 to 1994) (WMO 1998). In India, most of the cities are experiencing rapid urbanization and the majority of the country’s population is expected to be living in cities within a span of next two decades (CPCB 2010). Under National Air Quality Monitoring Programme (NAMP) 2008, annual average for SO₂ has not been exceeded in both the industrial (80%) & residential areas (93%) which is less than 20 ìg/ m³. Decreasing trend of SO₂ may be due to various interventions that have taken place in recent years such as reduction of sulphur in diesel, use of cleaner fuel such as CNG in Delhi etc. Also there has been a change in domestic fuel used from coal to LPG which may have contributed to reduction in ambient levels of SO₂. The total emission of NO_x in India is in the range of 3.4 to 4.6 Tg/year. The average annual concentration of NO₂ is reported to be 71µg/m³ in residential areas whereas 91µg/m³ in industrial areas during 2008. Various interventions have been taken place to mitigate ambient NO₂ levels but at the same time number of vehicles has been increased exponentially which is one of the major sources of NO₂ emission. During the same year i.e. 2008, the annual average concentration of RSPM is reported to be more in industrial areas (351 µg/ m³) as compared to residential areas (278 µg/m³). The reason for high particulate matter levels may be vehicles, gensets, small scale industries, biomass incineration, re-suspension of traffic dust, commercial and domestic use of fuels, etc. (CPCB 2008-09). In Delhi, the contribution of vehicular pollution has increased only in past 2-3 decades, earlier it was partly 23% in 1971 rose to 43% in 1981 and became 63% in 1991 (WWF 1995). There were 2.5 million vehicles registered in Delhi during 1996, while this number has reached 4.17 million in 2004 (MORTH 2004). Vehicular pollution accounts significantly to the total pollution generated in Delhi (Gurjar et al, 2004). After the implementation of CNG, only SO₂ concentrations develop a decreasing trend, whereas the NOx concentration seems to be increasing. The explanation for increasing NOx concentration seems to be related with the significant increase in total number of vehicles each year in Delhi and with the higher flash-point of CNG (540 °C) compared to that of diesel (232–282 °C). At such a high temperature, more nitrogen from the air compresses and reacts with oxygen in the combustion chamber of CNG driven vehicles and thus produces more NO_X. A study conducted by CPCB (2009) shows that 97% of hydrocarbon (HC), 76% of CO and 50% of NOx emission comes in air from vehicular activity and hence a fall/increase in the levels of these pollutants can be related to the CNG implementation. As per the studies done by various agencies, it has been observed that even after the implementation of CNG there is no improvement in the status of the pollutants except SO₂. Therefore, the objective of our present study is based on whether CNG conversion has impinged on the primary pollutant and tropospheric ozone pollution profile and for the improvement in the quality of air in post CNG period (2002-2009) at secondary data collection site (ITO-X) and generated data collection sites i.e. Site I (Yamuna Biodiversity Park, away from traffic intersection), Site II (Traffic intersection at outside YBP, outer ring road, Gandhi vihar), Site III (Aravalli Biodiversity Park, away from traffic intersection) and Site IV (traffic intersection at outside ABP, ring road, Vasant vihar). The data collected on generated sites was only performed in monsoon season (Aug-Sept, 2009).

Methodology

The secondary data of the air pollutants (NO₂, SO₂, SPM, RSPM, CO & O₃) were collected from ITO-X site in the last 7 years (2002-2009) from CPCB website (www.cpcb.nic.in). For generated data, four sites were selected which are distinct on the basis of two zones: Riverine zone [Site I - Yamuna Biodiversity Park (YBP), near Gandhi vihar, Delhi and Site II - Traffic intersection outside YBP, near Gandhi vihar, outer ring road, Delhi] and Hilly zone [Site III - Aravalli Biodiversity Park (ABP), inside Vasant Vihar, Delhi and Site IV – Traffic Intersection outside ABP Vasant Vihar, Ring Road, Delhi]. The sampling was done during monsoon season (Aug-Sept, 2009) for regularly 7 days with time interval of 8 hrs of both the pollutants one primary (NO₂) and secondary (O₃). High Volume Sampler (Model No: ENVIRO APM 430), was used to measure NO₂ at Site I & III. The instrument has been kept at the height 10 m above the ground. Simultaneously the hourly metrological data were also recorded at these sites at all the four selected sites with the help of pocket weather monitor (Kestrel, K3000-342127,USA). For the measurement of ground level ozone (O₃), ozone sensor (Model No: Aeroqual,Series 500), was used for regularly 7 days for 8 hrs at all the sites (Site I – IV).

Results and Discussion

For secondary data collection, primary pollutants which CPCB has been taken into account are NO₂ ,SO₂ ,SPM ,RSPM & CO and one of the secondary pollutants viz.O₃. The trend of fluctuation of primary and secondary pollutants in last 7 years (2002-2009) at ITO-X site has been compiled and taken in Fig.1(a-f). The highest concentration of NO₂ (126.66µg/m3) was reported in the year 2008 and in other reported years, either it crosses permissible limit (80µg/m³) or hovered around it (taken in Fig. 1a). So, it is quite interesting to note that even after the implementation of CNG programme in Delhi, NOx level is still showing increasing trend. It may be due to diesel vehicles whose sale in Delhi has registered an increase of 106% since 1999. These vehicles emits 3 times more NOx than petrol vehicles. Surprisingly, emission from a poorly maintained CNG fleet can also increase NOx because advanced testing facilities are not available for accurate NOx measurements (CSE 2004). Taken in Fig.1b), the concentration of ozone was highest (48.44µg/m³) in the year 2009. However, it did not cross the threshold level (80µg/ m³) for plant species as prescribed by NCLAN (National Crop Loss Area Network). Increase in ozone level may be due to the increase in precursor gases (NOx, CO, VOCs) (Leone and Seinfeld 1984). The profile of SO₂ (Taken in Fig.1c) shows highest concentration (22.57 µg/m³) in the year 2007. Interestingly, SO₂ is the only pollutant which shows significant decrease in the level after implementation of CNG programme. Here only, Government’s mitigation policy measures that appears to have had a positive impact on air quality. The reduction of sulphur dioxide in the ambient air is due to the lowering of suphur content of diesel and petrol which converts SO₂ to sulphates ( a fine particle) (Narain and Krupnick 2007) . We can notice taken in Fig. 1d, the highest concentration of CO ( 3028.228µg/m³ ) which was observed in the year 2002 and in other years (2002- 2009) either it crosses or have approached the threshold value ( 2000µg/m³). Taken in Fig.8e highest concentration of SPM ( 597.34 µg/m³) was recorded in the year 2009 and also in case of RSPM highest concentration ( 301.87µg/m³ ) was also recorded in the year 2009 (Taken in Fig.8f). In other years their concentration crossed their respective permissible limits (200µg/m³) for SPM and (100µg/ m³) for RSPM. After the implementation of CNG programme, these pollutants are not showing decreasing trend, rather their concentration is increasing due to poor three-wheeler technology which includes poor quality of piston rings as well as the improper maintenance of air filters (Narain and Krupnick 2007).

Table 1 : Meteorogical parameters observed at four Sites Click here to View table

Figure 1 (a-f): Trend pf Primary Pollutants (NO2, SO2, SPM & SPM) Click here to View figure

For generated data collection, as discussed in methodology section, four sites were taken into account. Yamuna Biodiversity Park (YBP) is designated as ‘away from traffic intersection’ (Site I) with dense vegetation monitoring site. The nitrogen dioxide (NO₂) and ground level ozone (O₃) monitoring was done during daytime (10:00a.m-6:00p.m) in monsoon month (20^th -27^th Aug’ 2009). Take in Fig.2, it is clearly depicted that the average concentration (for 7 days) of NO₂was found to be 2.92 µg/m³ and for O₃ was 23.25 µg/m³. The highest concentration of NO₂ (4.16 mg/m³) was recorded on 23^rd Aug’09 (4^th day) and for O₃ (27.1µg/m³) on 26^th Aug (6^th day). Moreover, from their diurnal profile, it has also been noticed that the high peaks of ozone were found at 12:00 hrs (26.87µg/m³) and at 14:00 hrs (30.98µg/m³). During the monsoon month, recorded concentrations of NO₂ and O₃ depicted that the peak levels were under the permissible limit for both the pollutants i.e. NO₂ (80µg/m³) and O₃ (80µg/m³). This observation can be supported in the earlier study at the same site (Saxena and Ghosh 2009) where they have already reported lower values of pollutant (ozone) during monsoon month as compared to summer and winter months. It is obviously due to the scavenging action of rain. Besides this, Table 1 also shows that recorded onsite meteorological data at Site I, where wind speed was little higher than other sites this can be a reason for the dispersion of pollutants which ultimately resulted in decrease in the concentration of NO₂ & O₃. At Site II (Traffic intersection outside YBP, Gandhi Vihar, outer ring road) has high density of vehicles (particularly heavy load trucks and buses) with less vegetation. During monsoon month, the ground level ozone (O₃) was monitored during daytime (10:00a.m.-6:00p.m) (10^th Aug -17^th Aug’2009). Taken in Fig.3, it was clearly depicted that the average concentration (for 7 days) of O₃ was 27.07 mg/m³. The highest concentration of O₃ (31.26mg/m³) (6^th day) and the lowest was 22.25 mg/m³. Moreover, from their diurnal profile, it has also been noticed that the high peaks were found at 13:00 pm (38.99mg/m³) and 15:00 hrs (41.75mg/m³). The recorded concentrations of O₃ depicted that the peak levels were also crossing the permissible limit. This is due to the fact that as compared to Site I, Site II had shown comparatively higher concentrations of ozone due to high emission of precursor gases from the heavy traffic flow as this site is located near outer ring road and comprised of heavy vehicles like trucks and buses, which accelerates the photochemical reactions. In general, as per previous studies (Saxena and Ghosh 2010), there were high concentrations of ozone in summer as well as in winter months but this study analyzes the concentration of ozone in monsoon season, that’s why the reported values were generally less due to the scavenging action by rain (Chan and Kwok 2001). Moreover, in case of tropospheric ozone there is non-availability of sufficient solar radiation and the diurnal amplitude of ozone which is found to be very small during monsoon months (Lal et al, 2000; Saraf et al, 2003 and Jain et al, 2004). Recorded onsite meteorological data at Site II (Table 1), was also clearly reported that due to increase in the rate of wind speed there is dispersion of pollutants which ultimately resulted in decreasing in the concentration of O₃ in monsoon period. Aravalli Biodiversity Park (ABP) is designated as ‘away from traffic intersection’ (Site III) with dense vegetation monitoring site. This site is closest to residential area of Vasant Vihar. The nitrogen dioxide (NO₂) and ground level ozone (O₃) monitoring was done during daytime (10:00a.m-6:00p.m) in monsoon month (22^nd -28^th Sept’ 2009). Take in Fig.4, it was clearly depicted that the average concentration (for 7 days) of NO₂ was found to be 5.72 mg/m³ and for O₃ was 19.70 mg/m³. The highest concentration of NO₂ (9.54 mg/m³) was recorded on 25^th Sept’09 (4^th day) and for O₃ (24.47 µg/m³) on 28^th Sept (7^th day). Moreover, from their diurnal profile, it has also been noticed that the high peaks of ozone were found at 14:00 hrs (21.54µg/m³) and 16:00 hrs (22.98µg/ m³). The recorded concentrations of NO₂ and O₃ depicted that the peak levels were under the permissible limit of both NO₂ (80µg/m³) and O₃ (80µg/m³) during the monsoon month. The values of O₃ are generally higher in summer and winter months at this site (Saxena et al, 2009) as per previous studies but our present study was conducted during monsoon month that’s why it has somewhat lower values of ozone due to the scavenging action of rain, besides this site was also away from traffic intersection area, therefore on site emission was less which ultimately gave rise to low concentration of pollutants (Lal et al, 2000). At Site IV (Traffic intersection outside ABP, Vasant Vihar, ring road) is a densely vegetative area about 3 km away from Site III (ABP) located near Vasant vihar at ring road with heavy traffic flow (particularly two- wheelers and buses). The ground level ozone (O₃) was monitored during daytime (10:00a.m.-6:00p.m) in monsoon month (15^th Sept – 21^st Sept’2009). Taken in Fig.5, it was clearly depicted that the average concentration (for 7 days) of O₃ was 21.74 µg/m³. The concentration of O₃ range from 24.55µg/m³- 19.54 µg/m³ (on 5^th and 3^rd day). Moreover, from their diurnal profile, it has also been noticed that the high peaks of ozone were found at 13:00 hrs (28.99µg/m³) and 15:00 hrs (35.15µg/ m³). The recorded concentrations of O₃ depicted that the peak levels were at below the threshold or permissible limit. Thus, the present study concludes that even after the implementation of CNG there is no remarkable progress in the variation of air pollutants except SO₂ in the last 7 years (2002-2009). Our generated data also suggests that variation in ozone concentration was very site specific. Concentration of secondary pollutant ozone was higher at site II & IV which are kerbside area, facing heavy traffic flow in comparison to vegetative site (site I & III).

Figure 2: Comparison of average concentration of NO2 & O3 in August 2009 at YBP (Site I) Click here to View figure

Figure 3: Comparison of average concentration of O3 in August 2009 at YBP & traffic intersection outside YBP (Site I & Site II) Click here to View figure

Figure 4: Comparison of average concentration of NO2 & O3 in September 2009 at ABP (Site III) Click here to View figure

Figure 5: Comparison of average concentration of O3 in September 2009 at ABP & traffic intersection outside ABP (Site III & Site IV) Click here to View figure

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