Atmospheric elemental carbon deposition from urban and suburban sites of Shanghai: Characteristics, sources and comparison with aerosols and soils

Elemental carbon (EC) in wet and dry deposition is an important chain of its transportation in urban surface system. However, little was known about this key process. Based on 90 samples from 13 consecutive months of atmospheric deposition sampling at typical urban and suburban sites in Shanghai, China, this research studied EC fluxes and amounts of dry and wet deposition, the relationship between EC and polycyclic aromatic hydrocarbons (PAHs) and possible sources of deposited EC. The difference of EC in deposition from those in other typical media was also discussed. Results showed that despite of lower flux in dry deposition than wet deposition, more atmospheric EC was removed by dry deposition during sampling period. EC bulk (i.e. dry and wet mixture) deposition amount was lower than the sum of wet and dry deposition. EC had a stronger correlation with PAHs than total organic carbon (TOC) did, indicating the important role of EC in carrying PAHs. The EC-cogenerated high molecular weight PAHs revealed that traffic, coal burning and biomass burning were the main sources of EC in atmospheric deposition. Unexpectedly, EC:TOC ratio in deposition, the link between aerosols and surface soils, was significantly different from (lower than) those in the two media, which can be attributed to the attenuation of organic carbon in coarser and easy-to-deposit atmospheric particles, the stability of the EC as well as other sources to soils.