Analysis of ambient formaldehyde in the eastern region of India along Indo-Gangetic Plain.

Ambient levels of formaldehyde (HCHO) were measured in the tropical urban mega city of Kolkata from July 2012 to April 2014, based on USEPA Compendium Method TO-11A using 2,4-dinitrophenylhydrazine (2,4-DNPH). The samples were analyzed by isocratic reverse-phase high-performance liquid chromatography (HPLC) with an ultraviolet detector at a wavelength of 360 nm. High values of HCHO were recorded at our site. The highest and average HCHO mixing ratio measured for the entire study period was 803 and 217 ppbv respectively. Seasonal wind regimes have been found to influence the seasonal pattern of HCHO mixing ratio at this site resulting in relatively higher mixing ratio of HCHO during the pre-monsoon periods as compared to the others. Apart from these, sampling-based measurements of CH4 and continuous measurements of ozone (O3) and CO were also performed with the objective to study the interrelationship of HCHO with these species. The results suggest the presence of highly complex chemistry among them.

Variability of SO2, CO, and light hydrocarbons over a megacity in Eastern India: effects of emissions and transport.

The Indo-Gangetic plain (IGP) has received extensive attention of the global scientific community due to higher levels of trace gases and aerosols over this region. Satellite retrievals and model simulations show that, in particular, the eastern part IGP is highly polluted. Despite this attention, in situ measurements of trace gases are very limited over this region. This paper presents measurements of SO2, CO, CH4, and C2-C5 NMHCs during March 2012-February 2013 over Kolkata, a megacity in the eastern IGP, with a focus on processes impacting their levels. The mean SO2 and C2H6 concentrations during winter and post-monsoon periods were eight and three times higher compared to pre-monsoon and monsoon. Early morning enhancements in SO2 and several NMHCs during winter connote boundary layer effects. Daytime elevations in SO2 during pre-monsoon and monsoon suggest impacts of photo-oxidation. Inter-species correlations and trajectory analysis evince transport of SO2 from regional combustion sources (e.g., coal burning in power plants, industries) along the east of the Indo-Gangetic plain impacting SO2 levels at the site. However, C2H2 to CO ratio over Kolkata, which are comparable to other urban regions in India, show impacts of local biofuel combustions. Further, high levels of C3H8 and C4H10 evince the dominance of LPG/petrochemicals over the study location. The suite of trace gases measured during this study helps to decipher between impacts of local emissions and influence of transport on their levels.