Observational study of aerosol hygroscopic growth factors over rural area near Beijing mega-city
1Chinese Academy of Meteorological Science, China Meteorological Administration, Beijing, China
2Nansen-Zhu International Research Centre, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
3Graduate University of Chinese Academy of Sciences, Beijing, China
Abstract. We investigated aerosol hygroscopic growth property and its influence on scattering coefficient using M9003 nephelometers in coupling with a relative humidity controlled inlet system at a rural site near Beijing mega-city (Jingjintang) from 24th April to15th May 2006. Inlet relative humidity was controlled in an increasing range of 40%–90% while the aerosol hygroscopic growth factor, f(RH=80%), varied in a range of 1.07–2.35 during the measurement. Estimated periodic mean values of aerosol hygroscopic growth factors are 1.27–1.34, 1.17–1.23, 1.55–1.59 and 2.33–2.48 for clean, dust, urban pollution and mixed pollution periods respectively. An examination of chemical composition of daily filter samples highlighted that aerosol hygroscopicity was generally enhanced with the increasing ratio of ammonium sulfate (AS) to organic matter (OMC). Furthermore, strong hygroscopic organic aerosols were observed on 11th (f(RH=80%)=2.23) and 15th (f(RH=80%)=2.21) of May with organic carbon proportions of PM2.1 reaching 42.3% and 43.0% respectively. Back-trajectory analysis indicated that solar radiation and vertical convective movement along the air mass pathway might strongly influence the hygroscopic properties of organic matter.