Measurements and analysis of criteria pollutants in New Delhi, India
Introduction
To protect air quality in the US, the US Environmental Protection Agency (EPA) has mandated air quality standards for the following six air pollutants (called the criteria pollutants): ozone (O3), lead (Pb), total suspended particulates (TSP/PM fine), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen oxides (NOx=NO+NO2). Collectively, these standards are called the National Ambient Air Quality Standards (NAAQS) (Table 1). The results for the analysis of CO, SO2, NOx, and TSP measurements made at the Income Tax Office (ITO) located on B.S.G. Marg in New Delhi, India will include the US NAAQS for comparison purposes.
CO is an important trace gas in the earth's atmosphere, which performs several important roles in the troposphere. There are a variety of sources, both natural and anthropogenic, for ambient CO. Natural sources include oxidation of methane and natural hydrocarbons, ocean emissions, and emissions from vegetation. In rural areas, these are the most dominant sources; therefore, in a remote location, CO is one of the most dominant precursors for photochemical ozone production Crutzen, 1973, Chameides and Walker, 1973, Parrish et al., 1991. In urban areas, however, anthropogenic sources, including fossil fuel combustion, industrial activities, biomass burning, and oxidation of anthropogenic hydrocarbons, contribute far more to the concentration of CO than the natural sources.
CO regulates the hydroxyl radical (OH) concentration in areas of less than a few parts per billion by volume (ppbv) of NOx=NO+NO2 Weinstock et al., 1980, Parrish et al., 1991. The lifetime of CO is approximately 1–3 months, representing the slow rate of mixing and the consumption by reaction with OH Seinfeld, 1986, Warneck, 1988, Parrish et al., 1991. As a result of its long lifetime, it can be used as an inert tracer of most recent CO emissions in an airmass. In the troposphere, a significant CO background concentration exists (∼150 ppbv in the Northern Hemisphere and ∼50 ppbv in the Southern Hemisphere) based on continuous CO production from the oxidation of methane and its long lifetime (Warneck, 2000). The background concentration is defined here as the annual mean surface-mixing ratio advected into an airshed at a particular location. The rural/remote CO concentration levels display a pronounced seasonal cycle associated with a theoretical seasonal cycle in the hydroxyl radical concentration Seiler et al., 1976, Dianov-Klokov and Yurganov, 1989. Studies have shown a direct link between the increase in anthropogenic emissions and a continuous increase in the background concentration level of CO Rinsland and Levine, 1985, Khalil and Rasmussen, 1988.
The history of a sampled airmass parcel may be explored further by the simultaneous measurements of CO with other atmospheric trace gases. This analysis allows for determining the emissions that the airmass has received and the photochemical transformation to which it has been subjected. In a situation where the photochemical transformations, including removal mechanisms, are negligible or can be accounted for adequately, a check of emission inventories is theoretically possible.
Both sulfur and nitrogen in the atmosphere originate either from natural processes or anthropogenic activity. SO2 is a prominent anthropogenic pollutant and contributes to the formation of sulfuric acid, the formation of sulfate aerosols, and the deposition of sulfate and SO2 at the ground surface. In the lower atmosphere, nitric oxide (NO) is converted to nitrogen dioxide (NO2) by reaction with peroxyradicals (RO2) or O3. The NO2 generated is then photolyzed in the atmosphere and the atomic oxygen released combines with molecular oxygen to form O3.
TSPs are the general term used for a mixture of solid particles and liquid droplets found in the air. These particles, which come in a wide range of sizes, originate from many different stationary and mobile sources as well as from natural sources. They may be emitted directly by a source or formed in the atmosphere by the transformation of gaseous precursor emissions such as SO2 and NOx. Their chemical and physical compositions vary depending on location, time of year, and meteorology. Scientific studies show a link between inhaleable particulates (i.e. PM fine) and a series of significant health effects. In addition, particulates cause adverse impacts on the environment via reduced visibility and changes in the nutrient balance through deposition processes (US EPA National Air Quality and Emissions Trends Report, 1997).
New Delhi, the capital of India, is the third most populated city of India and has a population of approximately 10 million. The city is located in central India (latitude 28°39′N, longitude 77°13′E) and approximately 715 ft above mean sea level (MSL). New Delhi is located in the subtropical belt with maximum temperature of 46°C in summer and minimum values of 1°C in winter. This area is under the influence of monsoonal winds (ranging from NE to NW in winter and ranging from SE to SW in the summer) (Varshney and Padhy, 1998), with average yearly rainfall of approximately 73 cm.
The city has grown at a phenomenal rate from 1971 to 1991. Automobiles have increased from 200,000 to 850,000 during this 20-year period. In addition to this large source of fossil fuel combustion, the increase in power production, biomass burning, number of landfills, and sewage treatment plants all contribute to the deterioration of ambient air conditions in New Delhi during the past 20 years (Sharma and Roychowdhury, 1996).
The data presented were collected by the Central Pollution Control Board (CPCB) from January 1997 through November 1998 at the ITO located on B.S.G. Marg in downtown New Delhi (Fig. 1). This data set was provided by Centre for Science and Environment, India. The objective of this analysis is to present findings linking pollutant concentrations, in terms of trends, to meteorology and anthropogenic activities in and around New Delhi as well as to determine the severity of the pollution from each source when compared to US NAAQS.
Section snippets
Results and discussion
Monthly average carbon monoxide concentrations (1 μg/m3 CO=0.86 ppbv) are plotted in Fig. 2 for 1997 and 1998. The data sets for both plots reveal a general trend of wintertime maximum concentrations and summertime minimum concentrations. A plausible explanation for these results may be found by examining meteorological conditions and photochemical activity at the site.
The general meteorology of the region during the winter is dominated by high pressure usually centered over western China
Integrated assessment
Solutions to the air quality problem must include a fully integrated assessment to include emission inventories, atmospheric modeling, environmental effects modeling, ambient concentration measurements, and socioeconomic analysis (Fig. 8). Emission inventories are needed to characterize pollutants and their sources, while the atmospheric modeling provides broad spatial and temporal coverage of the region and allows simulation of air quality during selected episodes. When the modeling provides
Conclusions
Continuous measurements of CO, NOx, SO2, and TSP were made in downtown New Delhi, India. All measured concentrations exceeded the US NAAQS except for SO2, while TSP was identified as exceeding the standard on the most frequent basis. This study revealed that background CO concentrations in New Delhi (∼1939 μg/m3) were much larger than background concentrations in the Eastern US (∼500 μg/m3) and Western US (∼200 μg/m3) and TSP concentrations were identified as being the largest violator of the
Acknowledgements
This paper was presented at the Workshop on Air Quality Index and Pollution Inventory for the City of Delhi, New Delhi, India on June 6–8, 2000. We thank the staff at the Centre for Science and Environment, New Delhi India for providing the data, which were obtained from the CPCB. The New Delhi air quality data were used as a case study in the Advanced Air Quality (NCSU MEAS 793B) graduate course.
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