Investigation of possible sources of water-soluble organic carbon particles observed with an online monitoring system

In this study, an instrument for the continuous measurements of water-soluble organic carbon (WSOC) component in fine particulate matter was developed and its field measurement results were presented. The instrument for collecting atmospheric aerosol particles for the online WSOC analysis uses an aerosol growth technology. Briefly, ambient particles, with aerodynamic diameters less than 2.5 μm, are collected via a cyclone inlet collector by rapidly mixing saturated water vapor with the ambient aerosol. The resulting supersaturated water vapor condenses on all the particles. The resulting liquid is separated from the air stream by an air–liquid separator, filtered, and the carbon content quantified using a total organic carbon analyzer, providing a continuous 4-min integral measurement. An evaluation of the accuracy of the online WSOC measurement system was performed by comparing the results with 24-h filter-based measurement data. The relationship between the 24-h averages of the 4-min data and the 24-h integrated data of the WSOC measurements indicated that the online WSOC concentration was 16% lower than that of the filter-based measurement.The online measurements of WSOC in fine particles were performed in September 2009 at a photochemical network near an industrial complex. Conditional probability functions were used to identify likely local emission source locations of the WSOC observed at the site, indicating that the major WSOC contribution to the site came mostly from the southeasterly (120−150°) and southwesterly (165–210°) directions, which brought air from a coal-fired power plant and traffic on the roads. Based on the temporal evolutions of SO2 and WSOC concentrations, wind direction with respect to the station angle of individual sources, wind speed, and source distance, it was shown that the presence of concurrent transients in SO2 and WSOC concentrations observed for a specific period is likely due to the influence of coal-fired power plants.

► An instrument for online measurements of WSOC particles is developed.
► An online method and integrated filter-based measurements of WSOC are compared.
► Excursions in the WSOC observed could be due to plumes from coal-fired power plant.