Seasonal variations of water soluble composition (WSOC, Hulis and WSIIs) in PM1 and its implications on haze pollution in urban Shanghai, China

• Water soluble fractions including Huils and WSOC in PM1 in Shanghai were presented.
• Hulis-C/WSOC in PM1 is lower than that of PM2.5 without obvious seasonal variation.
• Faster growth rate of Hulis-C than WSOC in haze episodes indicated higher ratio of Hulis-C/WSOC.
• Higher sulfate concentration was observed on clear days while higher nitrate was measured on serious haze days.
• The LWC is more sensitive to nitrate rather than sulfate and WSOC.

A year-long PM1 samples were collected at ECUST campus from April 2013 to February 2014 in urban Shanghai, China. Annual PM1 was (49.8 ± 31.8) μgm−3, comprising of water soluble organic carbon (WSOC), humic-like substances-carbon (Hulis-C), total water soluble inorganic ions (WSIIs) and liquid water content (LWC). Corresponding values were (5.51 ± 3.72) μgm−3, (2.20 ± 1.71) μgm−3, (22.52 ± 15.22) μgm−3 and (19.0 ± 19.2) μgm−3, respectively. Seasonal variation of PM1 was winter > spring > autumn > summer, while WSOC, Hulis-C, total WSIIs and LWC were highest in winter, with insignificant differences between spring, summer and autumn. Hulis-C and WSOC in PM1 on the serious haze day were found to be 4.4 and 2.5 times higher than those on the clear days, implying that Hulis might be very important for haze pollution. Among total WSIIs, sulfate was more abundant than nitrate on clear days while nitrate eventually surpassed sulfate in haze episodes. LWC in aerosol was significantly negative correlated with visibility and had strong relationship with nitrate and sulfate. It should be noted that LWC is four times sensitive to nitrate than sulfate, hence higher nitrate on haze days in Shanghai might facilitate the hygroscopic growth of aerosol.