title: Uncertainty in biogenic isoprene emissions and its impacts on tropospheric chemistry in East Asia.
abstract: In this study, the accuracy of biogenic isoprene emission fluxes over East Asia during two summer months (July and August) was examined by comparing two tropospheric HCHO columns (ΩHCHO) obtained from the SCIAMACHY sensor and the Community Multi-scale Air Quality (CMAQ v4.7.1) model simulations, using three available biogenic isoprene emission inventories over East Asia: i) GEIA, ii) MEGAN and iii) MOHYCAN. From this comparative analysis, the tropospheric HCHO columns from the CMAQ model simulations, using the MEGAN and MOHYCAN emission inventories (Ω(CMAQ, MEGAN) and Ω(CMAQ, MOHYCAN)), were found to agree well with the tropospheric HCHO columns from the SCIAMACHY observations (Ω(SCIA)). Secondly, the propagation of such uncertainties in the biogenic isoprene emission fluxes to the levels of atmospheric oxidants (e.g., OH and HO2) and other atmospheric gaseous/particulate species over East Asia during the two summer months was also investigated. As the biogenic isoprene emission fluxes decreased from the GEIA to the MEGAN emission inventories, the levels of OH radicals increased by factors of 1.39 and 1.75 over Central East China (CEC) and South China, respectively. Such increases in the OH radical mixing ratios subsequently influence the partitioning of HO(y) species. For example, the HO2/OH ratios from the CMAQ model simulations with GEIA isoprene emissions were 2.7 times larger than those from the CMAQ model simulations based on MEGAN isoprene emissions. The large HO2/OH ratios from the CMAQ model simulations with the GEIA biogenic emission were possibly due to the overestimation of GEIA biogenic isoprene emissions over East Asia. It was also shown that such large changes in HO(x) radicals created large differences on other tropospheric compounds (e.g., NO(y) chemistry) over East Asia during the summer months.
authors.affiliation: School of Environmental Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, Republic of Korea; Advanced Environmental Monitoring Research Center (ADEMRC), Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, Republic of Korea.
authors.forename: K M
authors.initials: KM
authors.lastname: Han
authors.forename: R S
authors.initials: RS
authors.lastname: Park
authors.forename: H K
authors.initials: HK
authors.lastname: Kim
authors.forename: J H
authors.initials: JH
authors.lastname: Woo
authors.forename: J
authors.initials: J
authors.lastname: Kim
authors.forename: C H
authors.initials: CH
authors.lastname: Song
keywords: Biogenic isoprene emission; CMAQ model; SCIAMACHY; Tropospheric HCHO columns