K. M. Han

Uncertainty in biogenic isoprene emissions and its impacts on tropospheric chemistry in East Asia.

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.

A budget analysis of NO x column losses over the Korean peninsula

In this study, the chemical and physical losses of nitrogen oxides (NOx) over the Korean peninsula were discussed in order to better understand the effects of the NOx losses on the tropospheric NO2 columns. Initially, it was found that the physical loss processes due to dry and wet depositions had almost negligible impacts on the NOx loss processes over the Korean peninsula. In contrast, the hourly NOx chemical column losses were large at ∼1014 molecules cm−2 h−1. The amounts of NOx removed for 1 hour account for approximately 33–35% of the episode-averaged tropospheric NO2 columns during summer over the Korean peninsula. The NOx chemical column loss rates were 24.1–70.9 times larger than the NOx physical column loss rates. In a budget analysis of the NOx chemical column losses, HNO3 formation via the reaction of OH + NO2 had the largest contribution toward the NOx chemical losses (42–55% during fall and winter seasons; 76–77% during spring; 92–93% during summer). Large amounts of NOx were also removed by heterogeneous nitrate formation via N2O5 condensation during the cold seasons (42–56%) over the Korean peninsula. The columnar NOx chemical losses took place mainly due to the two chemico-physical reaction processes, and also showed seasonal variations. PAN (Peroxyacetyl Nitrate) is another NO2 reservoir of potential importance. If the influence of the PAN-related chemistry on the NOx budget is considered, it can result in an approximate 69% increase in the NOx chemical column loss during summer. Such increases in the amounts of NOx removed for 1 hour due to the formation of PAN were equivalent to 56–58% of the episode-averaged tropospheric NO2 columns during summer over the Korean peninsula. Such active NOx chemical losses during summer are another main factor for the tropospheric NO2 columns exhibiting their smallest values during summer.

Ozone production efficiency of a ship-plume: ITCT 2K2 case study

Ozone production efficiency (OPE) of ship plume was first evaluated in this study, based on ship-plume photochemical/dynamic model simulations and the ship-plume composition data measured during the ITCT 2K2 (Intercontinental Transport and Chemical Transformation 2002) aircraft campaign. The averaged instantaneous OPEs (OPE(i)‾) estimated via the ship-plume photochemical/dynamic modeling for the ITCT 2K2 ship-plume ranged between 4.61 and 18.92, showing that the values vary with the extent of chemical evolution (or chemical stage) of the ship plume and the stability classes of the marine boundary layer (MBL). Together with OPE(i)‾, the equivalent OPEs (OPE(e)‾) for the entire ITCT 2K2 ship-plume were also estimated. The OPE(e)‾ values varied between 9.73 (for the stable MBL) and 12.73 (for the moderately stable MBL), which agreed well with the OPE(e)‾ of 12.85 estimated based on the ITCT 2K2 ship-plume observations. It was also found that both the model-simulated and observation-based OPE(e)‾ inside the ship-plume were 0.29-0.38 times smaller than the OPE(e)‾ calculated/measured outside the ITCT 2K2 ship-plume. Such low OPEs insides the ship plume were due to the high levels of NO and non-liner ship-plume photochemistry. Possible implications of this ship-plume OPE study in the global chemistry-transport modeling are also discussed.

Current Status and Development of Modeling Techniques for Forecasting and Monitoring of Air Quality over East Asia

Current status and future direction of air quality modeling for monitoring and forecasting air quality in East Asia were discussed in this paper. An integrated air quality modeling system, combining (1) emission processing and modeling, (2) meteorological model simulation, (3) chemistry-transport model (CTM) simulation, (4) ground-based and satellite-retrieved observations, and (5) data assimilation, was introduced. Also, the strategies for future development of the integrated air quality modeling system in East Asia was discussed in this paper. In particular, it was emphasized that the successful use and development of the air quality modeling system should depend on the active applications of the data sets from incumbent and upcoming LEO/GEO (Low Earth Orbit/Geostationary Earth Orbit) satellites. This is particularly true, since Korea government successfully launched Geostationary Ocean Color Imager (GOCI) in June, 2010 and has another plan to launch Geostationary Environmental Monitoring Spectrometer (GEMS) in 2018, in order to monitor the air quality and emissions in/around the Korean peninsula as well as over East Asia.