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Water-soluble humic-like substances (HULIS ws) are a group of heterogeneous organic compounds in the atmosphere, greatly impacting climate change and human health. As the most significant biomass burning (BB) and fossil fuel burning polluted area in China, Northeast China Plain could generate more light absorbing HULIS ws to the atmosphere. In this work, daily fine particle (PM 2.5) samples were collected in Changchun, located in Northeast China Plain, from October 17th to November 29th, 2016, to investigate the potential sources of optical properties of HULIS ws. Here, the whole sampling period was divided into three sub-periods using the density of fire spots and the timeline of the central heating: the non-heating (October 17th to October 24th), early heating (October 25th to November 13th), and normal heating (November 14th to November 29th) periods. The mean mass concentrations of HULIS ws were 4.2 ± 1.2, 8.6 ± 3.6, and 2.4 ± 1.3 μg m−3 during the non-heating, early heating, and normal heating periods, respectively. The positive matrix factorization (PMF) model results suggested that the contribution of primary BB, secondary BB, and fossil fuel burning emissions were 46%, 24%, and 19% during the non-heating period, 22%, 29%, and 17% during the early heating period, and 13%, 16%, and 50% during the normal heating period, respectively. Combining the PMF results with the random forest (RF) algorithm, the contribution of each source to the optical properties was quantified. Here, BB still dominated the optical properties of HULIS ws in Northeast China. During the study period, the primary BB and secondary BB contributed 25% and 34% in the light absorption coefficient (Abs), 22% and 33% in the mass absorption exponent (MAE), and 17% and 33% in the absorption Ångström exponent (AAE), respectively. Other sources like cooking and fossil combustion contributed 25% and 35% in Abs, 35% and 26% in MAE, and 16% and 33% in AAE, respectively. • 72% biomass burning emission contributed 40%–50% to light absorption parameters. • 4% cooking emission contributed 16%–35% to light absorption parameters. • This work provides a fast and easy way to quantify the contribution of sources to the light absorption properties. [ABSTRACT FROM AUTHOR]

We examined the characteristics and source apportionment of organic aerosols in ambient PM 2.5 samples collected during the late autumn in Changchun, Northeast China. 8 compound classes (>90 individual species) were detected in the aerosol samples, including biomass burning tracers, aliphatic lipids (fatty acids and fatty alcohols), secondary oxidation products, polycyclic aromatic hydrocarbons (PAHs), sugar compounds, hopanes and biogenic secondary organic aerosol (SOA) tracers. The concentrations of total quantified organic species ranged from 138.2 to 6.8 × 103 ng m−3, among which levoglucosan was the most abundant compound. Biomass burning tracers (anhydrosugars, lignin and resin acids) were the most abundant compounds, followed by fatty acids, secondary oxidation products, PAHs, sugar compounds and fatty alcohols. Biogenic SOA tracers and hopanes were less abundant. The homohopane index [defined as 31abS/(31abS + 31abR)] was 0.5, indicating a potential contribution of traffic emission. PAHs showed a dominance of benzo(b)fluoranthene (BbF), and the diagnostic ratios implicated a substantial contribution of petroleum combustion as well as coal combustion. 2-methylglyceric acid to 2-methyltetrols ratio (2.2) indicated that NOx influence isoprene oxidation products formation. Furthermore, the average ratio of cis-pinonic acid plus pinic acid to 3-hydroxyglutaric acid (31.4) revealed the much fresher α / β -pinene oxidation products to some extent. A good correlation was found between β -caryophyllinic acid and levoglucosan (r = 0.61), suggesting that β -caryophyllene can mainly be generated by biomass burning. The biogenic secondary organic carbon (SOC) was underestimated by the tracer-based method, which only occupied 0.4% of the organic carbon (OC). In contrast, PMF model indicated that emissions from fossil fuel combustion and biomass burning were most important, accounting for 42.4% and 33.6%, respectively, followed by biogenic SOA emission (17.0%) and fungal spore derived source (7.0%), suggesting biogenic aerosol is a nonnegative contributor. Fossil fuel combustion (42.4%) as well as biomass burning (33.6%) were most important contributors of organic aerosols in a typical city in Northeast China. Image 1 • The chemical and source characteristics of organic aerosols in Northeast China was studied. • 90 individual species were quantified with biomass burning tracers as most abundant compounds. • NOx influence SOA formation from isoprene. • Fossil combustion (42.4%) and biomass burning (33.6%) were most important contributors of OA. • Biogenic aerosol is a non-negligible contributor. [ABSTRACT FROM AUTHOR]