[On-line measurement of water-soluble composition of particulate matter in Beijing]

Concentrations of NO3(-), SO4(2), NH4(+) and Cl(-) were measured in Beijing during March, 2011, at a time resolution of 15 minutes using the system for rapid collection of fine particles and ion chromatography (RCFP-IC). Meteorological parameters were recorded concurrently to investigate the formation processes of typical pollutants. Five pollution episodes were observed in one month during the study period. All measured ions had similar temporal distributions showing saw-tooth cycle variations with slow accumulation and relatively rapid clearing. The peak concentrations of NO3(-) and NH4(+): in typical pollution episodes were observed to be about an order of magnitude higher than the background levels while the maximum concentrations of SO4(2-) and Cl(-) were only 2-4 times as high as the background values. Two episodes were observed during and after the home heating period. Compared to those during the home heating period, concentrations of the four ions after the home heating period were 15% -60% lower, implying that the home heating affected the concentration of ions. Measurements of ionic concentrations from RCFP-IC and those from the high time resolution of flight aerosol mass spectrometry (HR-TOF-AMS) during the study period were compared. The comparison results suggested the RCFP-IC was more reliable for the measurements of water soluble species.