WRF-Chem simulated surface ozone over South Asia during the pre-monsoon: Effects
of emission inventories and chemical mechanisms
Amit Sharma1,2, Narendra Ojha2, Andrea Pozzer2, Kathleen A. Mar3, Gufran Beig4, Jos Lelieveld2,5, and Sachin S. Gunthe11Department of Civil Engineering, Indian Institute of Technology Madras, Chennai, India 2Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany 3Institute for Advanced Sustainability Studies, Potsdam, Germany 4Indian Institute for Tropical Meteorology, Pune, India 5Energy, Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus
Received: 01 Dec 2016 – Accepted for review: 08 Dec 2016 – Discussion started: 09 Dec 2016
Abstract. We evaluate numerical simulations of surface ozone mixing ratios over the South Asian region during the pre-monsoon season employing three different emission inventories (EDGAR-HTAP, INTEX-B, and SEAC4RS) in the WRF-Chem model with the RADM2 chemical mechanism. Evaluation of modelled ozone and its diurnal variability, using data from a network of 18 monitoring stations across South Asia, show the model ability to reproduce the clean, rural and polluted urban environments over this region. In contrast to the diurnal average, the modelled ozone mixing ratios during the noontime i.e. hours of intense photochemistry (1130–1630 h Indian Standard Time or IST) are found to differ among the three inventories. This suggests that evaluations of the modelled ozone limited to 24-h average are insufficient to comprehend the uncertainties associated with ozone build-up. HTAP generally shows 10–30 ppbv higher noontime ozone mixing ratios than SEAC4RS and INTEX-B, especially over the north-west Indo-Gangetic Plain (IGP), central India and southern India. Further, the model performance shows strong spatial heterogeneity, with SEAC4RS leading to better agreement with observations over east and south India, whereas HTAP performs better over north and central India, and INTEX-B over west India. The Normalized Mean Bias (NMB in %) in the noontime ozone over the entire South Asia is found to be lowest for the SEAC4RS (~ 11 %), followed by INTEX-B (~ 12.5 %) and HTAP (~ 22 %). The HTAP simulation repeated with the alternative MOZART chemical mechanism showed even more strongly enhanced surface ozone mixing ratios (noontime NMB = 36.5 %) due to vertical mixing of enhanced ozone that has been produced aloft. The SEAC4RS inventory with the RADM2 chemical mechanism is found to be the most successful overall among the configurations evaluated here in simulating ozone air quality over South Asia. Our study indicates the need to also evaluate the O3 precursors across a network of stations to further reduce uncertainties in modelled ozone.
Sharma, A., Ojha, N., Pozzer, A., Mar, K. A., Beig, G., Lelieveld, J., and Gunthe, S. S.: WRF-Chem simulated surface ozone over South Asia during the pre-monsoon: Effects
of emission inventories and chemical mechanisms, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1083, in review, 2016.