Impact of Nitrogen Oxides, Volatile Organic Compounds and Black Carbon on Atmospheric Ozone Levels at a Semi Arid Urban Site in Hyderabad

Abstract

The surface level ozone (O 3 ), nitrogen oxides (NO x = NO 2 + NO), volatile organic compounds (VOCs), black carbon (BC) and meteorological parameters were continuously monitored for the period of one year (2010) at an urban site in Hyderabad using different trace gas monitors. The local emissions and meteorology have been found to play a significant role in diurnal variations of O 3 . The average peak time mixing ratios of O 3 were observed in the range of 23 ± 8 to 67 ± 13 ppbv. Diurnalseasonal variation of O 3 and its precursors were also reported. The observed O 3 concentrations were higher during the day than in the night. Maximum O 3 concentrations in the three seasons i.e., summer, winter and monsoon were 56 ± 14 ppbv, 50 ± 9 ppbv, and 28 ± 10 ppbv, respectively. Weekday/weekend variation of O 3 and its precursors were studied during the three seasons. High O 3 concentrations were observed on weekends compared to weekdays, however, NO x and BC levels were found low during weekends. The weekend effect of O 3 was high during winter. The annual average afternoon peak time O 3 levels on weekends were 11% higher than the weekday concentrations. Weekday/weekend variations of NO x at morning traffic rush hour were 14%, 9% and 8% in winter, summer and monsoon, respectively. The annual mean of NO x and BC concentrations at weekend were observed to be lower than weekday about 10% and 9% respectively. VOC/NO x ratio is more (5) during weekend than weekday (4) which resulted in enhanced O 3 formation.

Long Term Black Carbon Measurements at Two Urban Locations in New York

“…S1(b). BC concentrations reported here are similar to other locations in the USA (Jeong et al, 2004;Lough et al, 2006;Park et al, 2006) and Europe (Saha and Despiau, 2009) but lower than those observed at some Asian sites (Baxla et al, 2009;Salako et al, 2012;Swamy et al, 2012).…”

“…Similar diurnal profiles were observed at other urban locations Baxla et al, 2009;Saha and Despiau, 2009;Cheng et al, 2012;Swamy et al, 2012) although in some instances (Swamy et al, 2012) the weekday to weekend differences may not be as large as observed in New York. …”

“…S2(b), reflecting increased space heating use with the onset of colder periods. Maximum BC was also observed from November to February at urban locations in the USA , Europe (Saha and Despiau, 2009) India and Bangladesh (Baxla et al, 2009;Begum et al, 2012;Swamy et al, 2012). However in Hong Kong maximum BC was found from July to September (Cheng et al, 2012) indicating sources other than nearby traffic was impacting the site during the summer period.…”

“…The different day of week vehicle count pattern between the two sites reflects the size in the urban centers with roadways in the larger NYC urban center experiencing a more uniform total daily number of vehicles throughout the week. Elevated BC was observed during weekdays at other urban sites (Baxla et al, 2009;Saha and Despiau, 2009;Cheng et al, 2012;Swamy et al, 2012). Lough et al, (2006) found elevated EC and motor vehicle molecular markers during weekdays at Los Angeles.…”

Environmental monitoring of surface ozone and other trace gases over different time scales: chemistry, transport and modeling

“…Besides O 3 photochemistry, the other factors that influence the temporal/spatial distribution of O 3 and its precursors are concentration and emission rates of precursors (NO x /CO/VOCs) (Kleinman 1991), nature of precursor emission sources (traffic/anthropogenic/biogenic) (Swamy et al 2012b), boundary layer dynamics, meteorological parameters and heterogeneity of the terrain (i.e., geological site topography) (Jiménez et al 2006). …”