Polar organic tracers in PM(2.5) aerosols from forests in eastern China
Photooxidation products of biogenic volatile organic compounds, mainly isoprene and monoterpenes, are significant sources of atmospheric particulate matter in forested regions. The objectives of this study were to examine time series and diel variations of polar organic tracers for the photooxidation of isoprene and alpha-pinene to investigate whether they are linked with meteorological parameters or trace gases, and to determine their carbon contributions. In addition, the biogenic secondary organic carbon contributions from isoprene were estimated. PM(2.5) (particulate matter with an aerodynamic diameter <2.5 mu m) aerosol samples were collected from forests in eastern China and compared with data from forested sites in Europe and America. Aerosol sampling was conducted at four sites located along a gradient of ecological succession in four different regions, i.e. Changbai Mountain Nature Reserve (boreal-temperate), Chongming National Forest Park ( temperate), Dinghu Mountain Nature Reserve ( subtropical) and Jianfengling Nature Reserve in Hainan ( tropical) during summer periods when the meteorological conditions are believed to be favorable for photochemical processes. Fifty PM(2.5) samples were collected; eighteen organic compounds, organic carbon (OC), elemental carbon and trace gases were measured. Results indicate that the concentration trends of the secondary organic compounds reflected those of the trace gases and meteorological parameters. Very good correlations between the sum concentrations of isoprene oxidation products and atmospheric SO(2), O(3), NO(2), NO(x), as well as CO(2), at the Changbai site were found. The secondary OC due to isoprene was relatively high in tropical Hainan (0.27 mu gC/m(3)) where isoprene-emitting broadleaf species are dominant, but was comparable in boreal Changbai (0.32 mu gC/m(3)) where coniferous species are prevalent. The contribution of malic acid, which may have both biogenic and anthropogenic sources, to the OC mass was comparable at the four sites.