Aircraft measurements of gaseous pollutants and particulate matter over Pearl River Delta in China

Abstract

Measurements of gaseous pollutants (O 3, SO 2 and NO x ) and particulate matter (PM 10 and PM 2.5) were performed by means of an aircraft-sampling platform during the Program of Regional Integrated Experiments of Air Quality over Pearl River Delta 2004 (PRIDE-PRD2004, from 4 October 2004 to 5 November 2004). The objective was to characterize the spatial and vertical distributions of these air pollutants, and to analyze the associated trace elements and chemical species of PM 10 and PM 2.5. These vertical distributions are essential to understand, e.g. regional transport as well as the impact of aerosol on climate. The results indicate that the air pollution levels were severe over the PRD with the concentrations of NO x and O 3 reaching up to 160 and 100 ppb, respectively. The pollutants’ concentrations were generally decreasing with altitude in the boundary layer. Under certain meteorological conditions, vertical mixing plus horizontal transport can cause a high pollution level at the top of boundary layer. The pollutant concentrations were low over less industrialized and upwind regions. This suggests that local emission sources were the dominant cause of high pollution levels over the PRD. PM 2.5 were the main particulate pollutants over PRD. S, Ca, Fe, Al and Zn were the main trace elements found in the sampled particles, and the enrichment factors for elements were calculated to indicate that elements from anthropogenic origins are highly enriched in contrast to crustal composition. Chemical species analysis indicates that NH 4 + dominated, followed by SO 4 2−, NO 3 −, Ca 2+, Mg 2+, Cl −, Na + and K +. The equivalent ratio of SO 4 2− to NH 4 + is <1.0, showing that sulfate may mainly exist in the form of (NH 4) 2SO 4 and NH 4HSO 4. These results are valuable for studying vertical distribution characteristics of gaseous pollutants and particulate matters in the boundary layer over PRD and for providing important basic data to environmental assessment and decision-making.