Ravi Yadav

Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions

Ambient volatile organic compounds (VOCs) were measured using a high-resolution proton transfer reaction-time of flight-mass spectrometer at an urban site of Ahmedabad in India during the winter season in 2014. Mixing ratios of VOCs show large diurnal and day-to-day variations. Although strongly influenced by local emissions, periods of higher VOCs were observed during transport from the polluted Indo-Gangetic Plains than those from the cleaner Thar Desert. However with different rates, VOCs decreased exponentially with increasing wind speed. Relative abundance of methanol varied with weather conditions contributing highest and lowest under fog and clear-sky conditions, respectively. Among the compounds reported here, oxygenated VOCs (OVOCs) contribute to a large fraction (67–85%) with methanol being most abundant (40–58%). In spite of predominant vehicular emissions, diurnal distribution and emission ratios (ERs) of several VOCs indicate the role of biogenic and secondary sources. The ratios of isoprene/benzene and OVOCs/benzene show significant enhancements during daytime suggesting their contributions from biogenic and secondary sources. During marathon and cyclothon events, mixing ratios of VOCs were 2–10 times higher compared to a normal Sunday. The ERs of VOCs estimated using the nighttime data on marathon day are well within the range of values reported for several megacities of the world. The average contributions of primary anthropogenic sources to acetaldehyde, acetone, and isoprene were 44 ± 06%, 45 ± 07%, and 63 ± 12%, respectively. During cloudy condition, the increase in anthropogenic contribution to acetaldehyde (~10%), acetone (9%) and isoprene (30%) is due to reduction in biogenic emissions and secondary formation of these VOCs.

Distributions of ozone and related trace gases at an urban site in western India

Continuous in-situ measurements of surface ozone (O3), carbon monoxide (CO) and oxides of nitrogen (NOx) were conducted at Udaipur city in India during April 2010 to March 2011. We have analyzed the data to investigate both diurnal and seasonal variations in the mixing ratios of trace gases. The diurnal distribution of O3 showed highest values in the afternoon hours and lower values from evening till early morning. The mixing ratios of CO and NOx showed a sharp peak in the morning hours but lowest in the afternoon hours. The daily mean data of O3, CO and NOx varied in the ranges of 5–51 ppbv, 145–795 ppbv and 3–25 ppbv, respectively. The mixing ratios of O3 were highest of 28 ppbv and lowest 19 ppbv during the pre-monsoon and monsoon seasons, respectively. While the mixing ratios of both CO and NOx showed highest and lowest values during the winter and monsoon seasons, respectively. The diurnal pattern of O3 is mainly controlled by the variations in photochemistry and planetary boundary layer (PBL) depth. On the other hand, the seasonality of O3, CO and NOx were governed by the long-range transport associated mainly with the summer and winter monsoon circulations over the Indian subcontinent. The back trajectory data indicate that the seasonal variations in trace gases were caused mainly by the shift in long-range transport pattern. In monsoon season, flow of marine air and negligible presence of biomass burning in India resulted in lowest O3, CO and NOx values. The mixing ratios of CO and NOx show tight correlations during winter and pre-monsoon seasons, while poor correlation in the monsoon season. The emission ratio of ∆CO/∆NOx showed large seasonal variability but values were lower than those measured over the Indo Gangetic Plains (IGP). The mixing ratios of CO and NOx decreased with the increase in wind speed, while O3 tended to increase with the wind speed. Effects of other meteorological parameters in the distributions of trace gases were also noticed.

Regional biomass burning trends in India: Analysis of satellite fire data

The results based on the analysis of satellite fire counts detected by the Along-Track Scanning Radiometer (ATSR) sensors over different regions of India during 1998–2009 have been presented. Generally, the activities of open biomass burning show large spatial and temporal variations in India. The highest and lowest values of monthly fire counts were detected during the periods of March–May and July–September, respectively over different regions of India. The activities of biomass burning in two central states of Madhya Pradesh and Maharashtra were the highest and together accounted for about 25–45% of total annual fire counts detected over India during the study period. However, in opposite phases, the rainfall and fire count data show strong seasonal variation. In addition to large regional and seasonal variations, the fire data also show significant year-to-year variation. The higher annual fire counts exceeding the mean of entire period by about 16% and 43% were detected during the two periods of 1998–2000 and 2007–2009, respectively. We have estimated normalized anomaly of annual fire count data which shows large positive departures from long-term mean for the years 1999, 2007, 2008 and 2009, while negative departures for the years 2002, 2003 and 2005. Consistently, the mixing ratio of carbon monoxide (CO) typical peaks during winter but extended to pre-monsoon season during extensive fire years. The annual data over the entire region of India show lesser positive trend of about 3% yr−1. The inter-annual variation of fire count over entire India follows the trend in the ENSO Precipitation Index (ESPI) but shows opposite trend to the multivariate ENSO Index (MEI).