The regional chemical transport model, STEM, with advanced photochemical modules including SAPRC99 mechanism, KPP chemical solver and explicit photolysis scheme TUV, was applied to TRACE-P simulations and got good agreement with observations. We made a series of sensitivity simulations to investigate the influencing factors in East Asia: biomass burning, cloud and aerosol impacts on photolysis rates, and associated further influences on photochemical species. Detailed information can be found in:

Tang, Y. et al, Impacts of Aerosols and Clouds on Photolysis Frequencies and Photochemistry During TRACE-P, PART II: Three-Dimensional Study Using a Regional Chemical Transport Model. (submitted to J. Geophys. Res. special issue).Tang, Y., et al, The Influences of Biomass Burning during TRACE-P Experiment Identified by the Regional Chemical Transport Model. (submitted to J. Geophys. Res. special issue).Normal: baseline simulation considering both cloud and aerosol impactsNOAOD: without aerosol influencesCLEARSKY: without aerosol or cloud influencesThree-dimension Analysis for the Impacts of Clouds, Aerosols and Biomass burning during TRACE-P

Youhua Tang, Greg Carmichael, Jung-Hun Woo, Itsushi Uno, David Streets, Sarath Guttikunda, Narisara Thongboonchoo and other Co-authorsCenter for Global and Regional Environ. Research / Univ. Iowa, USAResearch Institute for Applied Mechanics/ Kyushu Univ. JapanArgonne National Laboratory, USACloud Top Temperature (C)Flight Altitude (m)The back trajectories that reached the paths of P3 flight 17 from 2 to 4 GMTO3 concentrations and productions of NORMAL and NOAOD simulations along the trajectory pathObserved and Simulated J[NO2] under three conditions show the strong cloud effects during the DC-8 flight 15The simulations for TRACE-P flights on March 27th clearly show the cloud and aerosol impacts on photolysis frequencies. If overcast clouds exist, clouds usually have stronger influences on local J-values than aerosols. The further influences on chemical species are determined not only by local conditions, but also by the airmass journey, especially for long-lived ozone. P3 flight 17 shows how O3 concentrations and productions changed under the aerosols influences along the journey passing three megacities.We successfully utilized the three-dimensional STEM model with detailed photochemistry and explicit photolysis calculations to simulate the TRACE-P airborne observations. The model is shown to have substantial skill in calculating photolysis rates over a broad range of cloud and aerosol conditions. These studies showed that both clouds and aerosols can impose significant impacts on J-values, short-lifetime radicals, and long-lived photochemical products and precursor species, and that the intensities of these impacts vary from scenario to scenario. In general the presence of clouds reduces photolysis rates below cloud and increases the rates above clouds. Asian aerosols are shown to largely reduce photolysis rates throughout the column. Short-lived photochemical species, like OH, HO2, and RO2, respond in accordance to local changes in J-values, and to local values of water vapor, methane, CO and other primary species. The influence of aerosols and clouds through photolysis rates on longer-lived species and secondary photochemical products is shown to be non-local, and instead dependent on the integrated history of the air mass. This is particularly important for the aerosol influence, as aerosols and precursor species are typically emitted and transported together in Asia, providing a longer period for aerosols to exert their influence. Biomass burning imposes complex influences on regional tropospheric chemistry, which can be divided into radiative and non-radiative influences. The biomass radiative influences contribute to OH, HO2, and O3 reduction, but increased HCHO concentrations by reducing its photolytic loss. Arranged by the sensitivity to the J-value change caused by biomass aerosols, we found that OH > HO2 > HCHO > O3 in regional average. Averaged over March, the biomass burning net influences reach up to 50% for OH, 40% for HO2, 60% for HCHO, and 10 ppbv for O3 below 1km. These highest influences usually appear in biomass burning areas or their adjacent downwind sites. The biomass airmasses emitted from Southeast Asia contain relatively high HCN (HCN/CO ~ 0.0015) and potassium (K+/CO ~ 0.0038), but very low NOy (NOy/CO ~ 0.005) mixing ratios, which may be associated with the special burning condition in this region. The biomass airmasses have extreme high ozone production efficiency. The observed O3/NOz values were ~ 17 in biomass events, and 1.7 in other events