Effects of Dry Deposition on Surface Ozone over South Asia Inferred from a Regional Chemical Transport Model

Abstract

Dry deposition is a major sink for tropospheric ozone; nevertheless, studies on its effects on ozone distribution are very limited over the rapidly developing South Asian region. We performed numerical simulations using the regional model WRF-Chem (Weather Research and Forecasting Model coupled with chemistry) to investigate the effect of dry deposition on surface ozone over this region by switching dry deposition ON–OFF in the model. Dry deposition of ozone is found to reduce ozone mixing ratios by up to ∼40% over the Indo-Gangetic Plain (IGP) and parts of western and central India. Additional enhancements (by up to ∼5 ppbv) in ozone are simulated when dry deposition for all gaseous species is switched off. We find a significant contrast on the effects of dry deposition from station to station as well as on the diurnal timescales over this region. The enhancements in ozone, caused by the absence of dry deposition, are lower over urban stations during nighttime, as compared to the rural and high-altitude stations. Significant enhancements in ozone levels in the absence of dry deposition over the mostly agrarian IGP underpin the importance of dry deposition particularly in the vegetated areas. The South Asian ecosystem is seen to act as an important sink of surface ozone via the dry deposition. The analyses partially fill a gap in the studies of dry deposition over the South Asian region, where this sink is anticipated to get perturbed following the changes in land use and land cover.