Abstract

This study examines various physical and chemical processes contributing towards an anomalous low surface ozone (O-3) event at a tropical urban site Bhubaneswar (20.29 degrees N, 85.83 degrees E) located in eastern India. Surface O-3 generally peaks during winter (similar to 40ppbv) at Bhubaneswa... Show moreThis study examines various physical and chemical processes contributing towards an anomalous low surface ozone (O-3) event at a tropical urban site Bhubaneswar (20.29 degrees N, 85.83 degrees E) located in eastern India. Surface O-3 generally peaks during winter (similar to 40ppbv) at Bhubaneswar. However, during 5-11 December 2010, surface O-3 decreased rapidly from 48 degrees ppbv on December 4 to 14 degrees ppbv on December 6. Average surface O-3 concentration before and after the event was 50.4 +/- 5.8ppbv and 47.8 +/- 2.4ppbv, respectively, with two-day running mean ranging from 15.5 to 30.5ppbv during the event. This event is analyzed using in situ surface O-3, meteorological parameters, backward air trajectories, and simulations using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Our analysis shows that this low O-3 event was driven by advection of cleaner low O-3 marine masses to Bhubaneswar associated with a rare low-pressure event over Bhubaneswar (occurred only once in winter during 2005-2014). Analysis of modeled spatial distribution of surface O-3 showed that this event was not confined to Bhubaneswar only and significantly reduced surface O-3 over a large area comprising most of the Indian land mass, the Bay of Bengal (BOB), and Burma as well. The study elucidates the importance of transport processes in controlling trace gas levels and highlights the advantage of Bhubaneswar as a strategic location to study atmospheric chemistry in contrasting air masses, i.e., polluted air masses from the Indo-Gangetic Plain (IGP) versus pristine air masses from the BOB. Show less