Climatic understanding of long-lasting high aerosol concentration episodes and the radiative effect over East Asia

Abstract

No other region in the world is as large and diverse a source of aerosols as the Asian continent. In particular, considerable amounts of air pollutants are generated in China, and the effects of trans-boundary transport of diverse aerosols including air pollutants on human health and regional climate are of multilateral concern in East Asia. Here, we firstly revealed the mechanism of occurrence and transport for the long-lasting high-PM10 episodes for 13 years (2001–2013) in Seoul, Korea and its link with air pollutants originating in China. Our result show that aerosols originating in China play a major role in the occurrence of multi-day (≥ 4 days) severe air pollution episodes in Seoul, Korea, where the concentration of PM10 exceeds 100 μg m3. Observations show that these multi-day severe air quality episodes occur when a strong high-pressure system resides over the eastern China - Korea region. Such a weather condition confines air pollutants within the atmospheric boundary layer and spread them by slow westerlies within the boundary layer from China into the neighboring countries. These particles lead to air quality deterioration in the short-term perspective, furthermore those result in the change in a radiation properties and an energy budget in the long-term perspective. Thus, in a climatic sense, we attempted an observationally based estimation of aerosol direct radiatve effect (DRE) for all-sky (both clear- and cloudy-sky) over East Asia (80°E–200°E, 20°N–60°N) for May 2000–December 2005. To reliably estimate all-sky DRE of aerosol over East Asia, we used a combing methodology between the measured a clear sky and the simulated DRE for a cloud sky in each 1°-grid. For the measured clear-sky DRE, we employed aerosol, cloud, and radiation fluxes from the Cloud and Earth's Radiant Energy System (CERES) instrument and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite. For the simulated cloudy-sky DRE, we performed radiative transfer modeling with the MODIS cloud properties in addition to the aerosol optical properties independently estimated in this study that include asymmetry factor and single scattering albedo. The results show that the global mean±standard deviation of DRE for the all-sky scene is −3.57±2.3 W m−2, which is weaker than that for the clear-sky only. This implies that DRE of both total and anthropogenic aerosol is considerably diminished by clouds interrupting solar reflection of aerosols. Particularly, for oceanic area of study domain with optically thick and a large amount cloud, the dimming effect by aerosols is amplified, which results in positive aerosol DRE for all-sky. Understanding such dynamical processes is a key for advancing the predictability of trans-boundary air pollutants and their health impacts in East Asia as well as developing international measures to improve air quality for the region. And further, evaluation of aerosol DRE for all-sky condition would contribute to reduce the large uncertainty by aerosols over East Asia, which can give some insight to simulate the future climate in model.