Radiative Impacts of Urban Aerosols in Seoul, Korea

1. IAIA2007 (June 3~8, 2007, COEX, Seoul, South Korea) Radiative Impacts of Urban Aerosols in Seoul, Korea Jiyoung Kim and Byoung-Cheol Choi Applied Meteorology Research Team National Institute of Meteorological Research Korea Meteorological Administration

2. Introduction • Atmospheric Aerosols: • A tiny particle suspended in the atmosphere (size range: ~nm to ~10 um) • Adverse effect on human health • Visibility impairments • Impacts on urban climate and meteorology • (heat island, heavy precipitation) Radiative impacts of aerosol => visible light scattering and absorption

3. Aerosol Sources in East Asia SO2 NOx Terra/MODIS AOD @ 0.55m (April 2000 ~ September 2005) NH3 NMVOC Anthropogenic Emission Asian Dust Storm Biomass Burning

4. Various Adverse Impacts of Urban Aerosols Urban Climate (UHI, Radiation budget) Urban Meteorology (cloud formation, precipitation process) Industrial Activity (agriculture, machine industry) Urban Aerosols Urban Environment (urban air quality, visibility) Health Impacts (respiratory system, CVD) Acid Deposition (destruction of cultural monuments)

5. Objectives of This Study • To overview the importance of atmospheric aerosols in urban climate and environment issues • To characterize optical properties of urban aerosol observed in Seoul, Korea • To investigate the radiative impact of the urban aerosols

6. Data and Radiative Transfer Model • AERONET (Aerosol Robotic Network) : operated by NASA/GSFC • Aerosol Optical Depth (AOD) at Seoul Site (Seoul National Univ.) • - spectral AOD @ 440, 675, 870, 1020 nm and water vapor (cm) • - data period : November 2000 to February 2003 • - level 2.0 (quality assured data) • Fu & Liou RTM model was employed (Fu and Liou, JAS 1993) • Surface albedo: IGBP 17-ocean type • Time interval: 30 minutes; Meteorological profiles: • Aerosol optical properties: OPAC data (Hess et al., BAMS 1998)

7. Aerosol Optical Depth at Seoul Beijing Seoul Kim et al. (AE 2007) • AOD maximum in June : - anticyclonic atmospheric circulation system in early summer (build-up of pollutants, prolonged dry or less rainy days, less scavenging) - hygroscopic growth of hydrophilic fine urban pollution aerosols - medium-range transported biomass burning aerosol from eastern China

8. Results of AOD Measurements at Seoul • Statistical Summary of AOD at Seoul - Spectral wavelength : 440 nm Average AOD : 0.50, S.D. of AOD : 0.37 Maximum : 2.58, Minimum : 0.12 - Spectral wavelength : 675 nm • Average AOD : 0.29, S.D. of AOD : 0.23 • Maximum : 1.57, Minimum : 0.06

9. Urban Aerosol Optical Properties (Hess et al., BAMS 1998)

10. OPAC (continued) Urban aerosol represents strong pollution in urban areas. The mass density of soot is 7.8 ug m-3, and the mass densities of both water-soluble substance and insoluble substance are about twice those of the continental polluted aerosol as found in center areas of large cities.

11. What is Aerosol Radiative Forcing? • Radiative impacts of aerosols: • Direct, Indirect(1st, 2nd), Semi-Direct • Shortwave vs. Longwave/ Surface vs. TOA • ∆F = Fnet - Fneto : Direct ARF (unit : W/m2) • Fnet= F↓ - F↑= F↓-F↓ = (1-α)F↓ • where Fnet = net flux (with aerosol) • Fneto = net flux at pristine (without aerosol) • Assume: no cloud, same atmospheric profile (T, P, H2O, CO2, O3, etc)

12. Diurnal Variation of ARF

13. Diurnal Variation of ARF

14. AOD Influences on URBAN ARF

15. Diurnal Variation of ARF

16. Conclusion and Discussion • Mean of aerosol optical depth at 440 nm obtained from AERONET measurements found to be 0.50 at Seoul, Korea. • Radiative transfer model was employed to estimate direct aerosol radiative forcing due to urban aerosol. 24-hr and daylight averaged ARF at AOD of 0.5 @ 550 nm found to be -30.2 and -53.3 W/m2, respectively. • Direct and indirect impacts on urban meteorology and climate need to be carried out through both well-designed measurements and model studies.