1Chinese Academy of Meteorological Sciences, Beijing, China
2Chinese Research Academy of Environmental Sciences, Beijing, China
3Max Planck Institute for Chemistry, Mainz, Germany
4Cyprus Institute, Nicosia, Cyprus
5King Saud University, Riyadh, Saudi Arabia
†deceased, March 2010
Abstract. In the past decades, regional air pollution characterized by photochemical smog and grey haze-fog has become a severe environmental problem in China. To investigate this, a field measurement campaign was performed in the Huabei region, located between 32°–42° N latitude in Eastern China, during the period 2 April–16 May 2006 as part of the project "Influence of Pollution on Aerosols and Cloud Microphysics in North China" (IPAC-NC). It was found that strong pollution emissions from urban and industrial centers accumulate in the lower atmosphere over the core area of Huabei. We observed widespread, very high SO2 mixing ratios, about 20–40 ppbv at 0.5–1.5 km altitude and 10–30 ppbv at 1.5–3.0 km altitude. Average CO mixing ratios were 0.65–0.7 ppmv at 0.5–1.5 km altitude, and very high CO around 1 ppmv was observed during some flights, and even higher levels at the surface. The high pollution concentrations were associated with enhanced levels of OH and HO2 radicals, calculated with a chemical box model constrained by the measurements. The maximum OH concentration was 6.9 × 106 molecules cm−3 (~0.29 pptv) at an altitude of ~1 km, remarkably higher than 5.4 × 106 molecules cm−3 (~0.22 pptv) at the surface. In the upper part of the boundary layer and in the lower free troposphere, high CO and SO2 competed with relatively less NO2 in reacting with OH, being efficiently recycled through HO2, preventing a net loss of HOx radicals. In addition to reactive hydrocarbons and CO, the oxidation of SO2 caused significant ozone production over Huabei (up to ~13% or 2.0 ppbv h−1 at ~0.8 km). The enhanced OH increased the formation of condensable species by the oxidation of volatile precursor gases, adding to the high loadings of mineral dust particles. Our results indicate that the lower atmosphere over Huabei is not only strongly polluted but also acts as an oxidation pool over Eastern China.