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Knowledge of aerosol chemistry in densely populated regions is critical foreffective reduction of air pollution, while such studies have not beenconducted in Changzhou, an important manufacturing base and populated city inthe Yangtze River Delta (YRD), China. This work, for the first time,performed a thorough chemical characterization on the fine particulate matter(PM2.5) samples, collected during July 2015 to April 2016 across fourseasons in this city. A suite of analytical techniques was employed tomeasure the organic carbon (OC), elemental carbon (EC), water-soluble organiccarbon (WSOC), water-soluble inorganic ions (WSIIs), trace elements, andpolycyclic aromatic hydrocarbons (PAHs) in PM2.5; in particular, anAerodyne soot particle aerosol mass spectrometer (SP-AMS) was deployed toprobe the chemical properties of water-soluble organic aerosol (WSOA). Theaverage PM2.5 concentration was found to be108.3 µg m−3, and all identified species were able toreconstruct ∼ 80 % of the PM2.5 mass. The WSIIs occupied abouthalf of the PM2.5 mass (∼ 52.1 %), with SO42−,NO3−, and NH4+ as the major ions. On average, nitrateconcentrations dominated over sulfate (mass ratio of 1.21), indicating thattraffic emissions were more important than stationary sources. OC and ECcorrelated well with each other and the highest OC ∕ EC ratio (5.16)occurred in winter, suggesting complex OC sources likely including bothsecondary and primary ones. Concentrations of eight trace elements (Mn, Zn,Al, B, Cr, Cu, Fe, Pb) can contribute up to ∼ 5.0 % of PM2.5during winter. PAH concentrations were also high in winter(140.25 ng m−3), which were predominated by median/high molecularweight PAHs with five and six rings. The organic matter including bothwater-soluble and water-insoluble species occupied ∼ 21.5 %of the PM2.5 mass. SP-AMS determined that the WSOA had average atomicoxygen-to-carbon (O ∕ C), hydrogen-to-carbon (H ∕ C),nitrogen-to-carbon (N ∕ C), and organic matter-to-organic carbon(OM ∕ OC) ratios of 0.54, 1.69, 0.11, and 1.99, respectively. Sourceapportionment of WSOA further identified two secondary OA (SOA) factors (aless oxidized and a more oxidized oxygenated OA) and two primary OA (POA)factors (a nitrogen-enriched hydrocarbon-like traffic OA and a local primaryOA likely including species from cooking, coal combustion, etc.). On average,the POA contribution outweighed SOA (55 % vs. 45 %), indicating theimportant role of local anthropogenic emissions in the aerosol pollution inChangzhou. Our measurement also shows the abundance of organic nitrogenspecies in WSOA, and the source analyses suggest these species are likelyassociated with traffic emissions, which warrants more investigations on PMsamples from other locations

Chemical characterization of fine particulate matter in Changzhou, China, and source apportionment with offline aerosol mass spectrometry