| Title: | Photochemical evolution of air in a tropical urban environment of India: A model-based study |
| Author(s): | Soni M; Girach I; Sahu LK; Ojha N; |
| Address: | "Physical Research Laboratory, Ahmedabad, India; Indian Institute of Technology, Gandhinagar, Gujarat, India. Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram, India; Presently at Space Application Centre, Indian Space Research Organisation, Ahmedabad, India. Physical Research Laboratory, Ahmedabad, India. Physical Research Laboratory, Ahmedabad, India. Electronic address: ojha@prl.res.in" |
| DOI: | 10.1016/j.chemosphere.2022.134070 |
| ISSN/ISBN: | 1879-1298 (Electronic) 0045-6535 (Linking) |
| Abstract: | "The photochemical processes over tropical Indian region impact the atmospheric composition and air quality over local to global scales; nevertheless, studies on detailed atmospheric chemistry remain sparse in this region. In this study, we investigate the photochemical evolution of air in the downwind of a tropical semi-arid urban environment (Ahmedabad) in India using the Master Mechanism model. The 5-days long chemical evolution has been simulated for the winter conditions - when this region experiences strong ozone build up. Model environment has been set up by including the meteorological conditions, overhead ozone, and aerosol loading, etc. Nitrogen oxides (NO(x)), carbon monoxide (CO), ozone (O(3)), and several volatile organic compounds (VOCs) have been initialized in the model based on the wintertime observations. The model predicts large O(3) production ( approximately 115 ppbv) in the downwind regions, followed by a gradual decrease from the 3(rd) day onwards. Additionally, significant amounts of the secondary inorganics, e.g. nitric acid ( approximately 17 ppbv), hydrogen peroxide ( approximately 9 ppbv), and organics, e.g. ketones ( approximately 11 ppbv), are also simulated. The noontime maximum levels of hydroxyl (OH) and hydroperoxyl (HO(2)) radicals are simulated to be 0.3 and 44 pptv, respectively. While the production of OH is dominated by the reaction of NO with HO(2) on the first day, photolysis of O(3) dominates subsequently with reduction in NO(x) levels. VOCs are the major OH sink during day 1, however contribution of CO is greater on further days. The air mass trajectory analysis suggests the outflow of ozone-rich air over the rural areas and the Arabian Sea, in agreement with measurements and a global model. Our study highlights the strong impact of the urban outflows on the regional atmospheric composition. The continuous measurements of VOCs and radicals are needed over tropical regions to complement the models and further improve the understanding of air chemistry" |
| Keywords: | *Air Pollutants/analysis *Air Pollution/analysis Environmental Monitoring *Ozone/analysis *Volatile Organic Compounds/analysis Air quality Box modeling Radicals South Asia Surface ozone Trace gases Urban pollution VOCs; |
| Notes: | "MedlineSoni, Meghna Girach, Imran Sahu, Lokesh K Ojha, Narendra eng England 2022/03/02 Chemosphere. 2022 Jun; 297:134070. doi: 10.1016/j.chemosphere.2022.134070. Epub 2022 Feb 26" |
