ABSTRACT: Seven year data of hourly surface ozone concentration is analyzed to study diurnal cycle, trends, excess of ozone levels above
threshold value and cumulative ozone exposure indices at a tropical megacity, Delhi. The ozone levels clearly exhibit a diurnal
cycle, similar to what has been found in other urban places. A sharp increase in the ozone levels during forenoon and a sharp
decrease in the early afternoon can be observed. The average rate of increase in ozone concentration between 09 and 12h has
been observed to be 7.1ppbh−1. We find that the daily maximum and daytime 8-h (10–17h) ozone levels are increasing at a rate of about 1.7 (± 0.7) and
1.3 (± 0.56) ppb y−1, respectively. The directives on ozone pollution in ambient air provided by United Nations Economic Commission for Europe
and World Health Organization for vegetation (AOT40) and human health protection were used to assess the air quality. The
present surface ozone levels in the city are high enough to exceed “Critical Levels” which are considered to be safe for human
health, vegetation and forest. The human health threshold was exceeded for up to ~45days per year. The AOT40 (Accumulated
exposure Over a Threshold of 40ppb) threshold was exceeded significantly during winter (D-J-F) and pre-monsoon (M-A-M) (Rabi
crop growing season) season in India. Translating AOT40 exceedances during pre-monsoon into relative yield loss we estimate
yield loss of 22.7%, 22.5%, 16.3% and 5.5% for wheat, cotton, soybean and rice, respectively.
Journal of Atmospheric Chemistry 04/2012; 60(3):237-252. · 0.99 Impact Factor
ABSTRACT: We present diurnal variation of ambient ammonia (NH3) in relation with other trace gases (O3, CO, NO, NO2, and SO2) and meteorological parameters at an urban site of Delhi during winter period. For the first time, ambient ammonia (NH3) was monitored very precisely and continuously using ammonia analyzer, which operates on chemiluminescence method. NH3 estimation efficiency of the chemiluminescence method (>90%) is much higher than the conventional chemical trapping method
(reproducibility 4.5%). Ambient NH3 concentration reaches its maxima (46.17ppb) at night and minimum during midday. Result reveals that the ambient ammonia
(NH3) concentration is positively correlated with ambient NO (r
2 = 0.79) and NO2 (r
2 = 0.91) mixing ratio and negatively correlated with ambient temperature (r
2 = − 0.32). Wind direction and wind speed indicates that the nearby (~500m NW) agricultural fields may be major source of
ambient NH3 at the observational site.
Environmental Monitoring and Assessment 04/2012; 162(1):225-235. · 1.40 Impact Factor
Journal of Earth Science and climate change. 05/2010;
Journal of Environmental Sciences 01/2010; 22:1023-1028. · 1.66 Impact Factor
Environmental Monitoring and Assessment 01/2010; 162:225-235. · 1.40 Impact Factor
ABSTRACT: We present the diurnal and seasonal variability of ambient NH3, NO, NO2 and SO2 over Delhi, India. Ambient NH3, NO and NO2 were measured continuously during winter, summer and autumn seasons using NH3- and NOx-analyzer, which operates by chemiluminescence method with a higher estimation efficiency (> 90%) than the chemical trap method (reproducibility 4.7%). Prominent diurnal, day-to-day and seasonal variations of ambient mixing ratio of NH3, NO, NO2 and SO2 were observed during the study period. Seasonal variation with higher mixing ratio in winter was observed for all measured trace gases except NO. Day-night variation of all measured trace gases observed was higher in winter in comparison with summer. Late morning increase in NO2 mixing ratio might be attributed to conversion of NO to NO2 with the interaction of O3.
Journal of Environmental Sciences 01/2010; 22(7):1023-8. · 1.66 Impact Factor
ABSTRACT: Characteristics of trace gases (O sub(3), CO, CO sub(2), CH sub(4) and N sub(2)O) and aerosols (particle size of 2.5 micron) were studied over the Arabian Sea, equatorial Indian Ocean and southwest part of the Bay of Bengal during the monsoon transition period (October–November, 2004). Flow of pollutants is expected from south and southeast Asia during the monsoonal transition period due to the patterns of wind flow which are different from the monsoon period. This is the first detailed report on aerosols and trace gases during the sampled period as the earlier Bay of Bengal Experiment (BOBMEX), Arabian Sea Monsoon Experiment (ARMEX) and Indian Ocean Experiments (INDOEX) were during monsoon seasons. The significant observations during the transition period include: (1) low ozone concentration of the order of 5 ppbv around the equator, (2) high concentrations of CO sub(2), CH sub(4) and N sub(2)O and (3) variations in PM2.5 of 5–20 mu g/m sup(3).