Vertical characteristics of carbonaceous species and their source contributions in a Chinese mega city

In this work, two new chemical mass balance (CMB) models were applied to estimate the possible source contributions to organic carbon (OC) and the secondary OC (SOC) concentrations in PM10 at 10, 40, 120 and 220 m heights on a meteorological tower in Tianjin. The OC and EC (elemental carbon) were simultaneously measured at the four heights from 24 August to 12 September 2009. The vertical characteristics of OC and EC showed a general decreasing trend with the increasing height. The SOC concentrations were then estimated by the minimum OC/EC ratio method, the NCPCRCMB model and the CMB-Iteration method. The results suggest increasing trends for SOC/TOC and SOC/PM10 up the tower. Additionally, wind rose maps and hourly 72-h back trajectory cluster maps were combined with the source apportionment results to discuss the vertical source contributions to OC, indicating that the percentage contributions of long-range transport sources (such as soil dust and SOC sources) increased with height. SOC formation and transportation by wind affected OC more strongly than each primary source at greater heights. Finally, the levels and sources of the excess OC (the difference between OC concentrations at lower heights to that at 220 m) are discussed. The results suggest that it is more effectively managed for reducing OC to control vehicle and coal sources at the ground level in Tianjin. Information about the more significant sources of excess OC can be used for the development of effective control strategies.