Impacts of chemical degradation of levoglucosan on quantifying biomass burning contribution to carbonaceous aerosols: A case study in Northeast China.

Biomass burning (BB) is an important source of carbonaceous aerosols in Northeast China (NEC). Quantifying the original contribution of BB to organic carbon (OC) [BB-OC] can provide an essential scientific information for the policy-makers to formulate the control measures to improve the air quality in the NEC region. Daily PM2.5 samples were collected in the rural area of Changchun city over the NEC region from May 2017 to May 2018. In addition to carbon contents, BB tracers (e.g., levoglucosan and K+BB, defined as potassium from BB) were also determined, in order to investigate the relative contribution of BB-OC. The results showed that OC was the dominant (28%) components of PM2.5 during the sampling period. Higher concentrations of OC, levoglucosan, and K+BB were observed in the autumn followed by the winter, spring, and summer, indicating that the higher BB activities during autumn and winter in Changchun. By using the Bayesian mixing model, it was found that burning of crop residues were the dominant source (65-79%) of the BB aerosols in Changchun. During the sampling period, the aging in air mass (AAM) ratio was 0.14, indicating that ~86% of levoglucosan in Changchun was degraded. Without considering the degradation of levoglucosan in the atmosphere, the BB-OC ratios were 23%, 28%, 7%, and 4% in the autumn, winter, spring, and summer, respectively, which were 1.4-4.8 time lower than those (14-42%) with consideration of levoglucosan degradation. This illustrated that the relative contribution of BB to OC would be underestimated (~59%) without considering degradation effects of levoglucosan. Although some uncertainty was existed in our estimation, our results did highlight that the control of straw burning was an efficient way to decrease the airborne PM2.5, improving the air quality in the NEC plain.

[Source Apportionment and Health Risk Assessment of Polycyclic Aromatic Hydrocarbons in PM2.5 in Changchun City, Autumn of 2017].

In this study, 30 PM2.5 samples were collected from the atmosphere in Changchun City in the autumn of 2017. The concentration and composition characteristics of 17 polycyclic aromatic hydrocarbons (PAHs) in the samples were analyzed by gas chromatography mass spectrometry (GC-MS). The diagnostic ratio and principal component analysis method were used to determine the source of PAHs pollution. The health risk assessment was carried out by both calculating the equivalent carcinogenic concentration of benzo(a)pyrene and the lifetime risk of cancer. Results show that the average PM2.5 concentration in autumn in Changchun is (50.84±12.23) µg·m-3, and the content of organic carbon (OC) and elemental carbon (EC) are (17.07±5.64) µg·m-3 and (1.33±0.75) µg·m-3, respectively, accounting for 37% of the total PM2.5. The total concentration of PAHs is (15.69±5.93) ng·m-3, which was dominated by medium- to high-ring-number PAHs, accounting for 84.26% of total PAHs. The atmospheric PAHs in Changchun mainly originate from motor vehicle exhaust emissions (44.48%) > coal combustion (29.16%) > biomass burning (26.36%), local transportation (gasoline vehicles) emissions being the main source of pollution. The average carcinogenic concentration of benzo(a)pyrene is in the range of 1.55 ng·m-3 and 5.38 ng·m-3, and the average carcinogenic equivalent concentration is (6.44±1.53) ng·m-3, which is generally considered a slight pollution level. The ingestion of PAHs by breathing is the most harmful to the health of adult women, followed by adult males and children, however since the lifetime carcinogenic risk value of the entire population did not exceed 1×10-6, their health risks are considered to be at acceptable levels.

[Effect of Biomass Burning on the Light Absorption Properties of Water Soluble Organic Carbon in Atmospheric Particulate Matter in Changchun].

To investigate the effect of biomass burning in Changchun in autumn on the absorbance of water-soluble organic carbon (WSOC) on PM2.5, PM2.5 samples were collected from October to November 2017. The light absorption characteristics of WSOC, carbonaceous components, and carbohydrate content in PM2.5 were analyzed. The study showed that the average concentrations of WSOC, organic carbon (OC), and elemental carbon (EC) in PM2.5 in Changchun were (10.12±3.47), (17.07±5.64), and (1.34±0.75) µg·m-3, respectively; the average contribution rate of secondary organic carbon (SOC) to OC was 38.93%. The total sugar concentration in Changchun is (1049.39±958.85) ng·m-3, of which the content of anhydroglucose (L-glucan, galactan, and mannan), as a biomass burning tracer in total sugar, was 91.69%. The results of sugar correlation analysis showed that biomass combustion was the main source of contribution to carbohydrates in the autumn of Changchun. The light absorption wavelength index of WSOC in autumn was 5.75±1.06, and the unit mass absorption efficiency was (1.23±0.28) m2·g-1, indicating that biomass combustion has an important influence on WSOC absorbance. The biomass combustion characteristic source parameter was used to quantify the contribution of biomass burning to WSOC concentration, which was found to be 58.82%, while the contribution to total WSOC light absorption was 40.92%.

[Molecular Composition and Source Apportionment of Fine Organic Aerosols in Autumn in Changchun].

Organic aerosols have attracted increasing attention recently due to their significant contribution to fine particles (PM2.5) and their complex components and sources. In this study, a total of 40 PM2.5 samples were collected simultaneously with high-volume samplers in Changchun from 16th Oct to 29th Nov 2016. Organic carbon (OC), elemental carbon (EC), non-polar organic compounds including n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and hopanes, and levoglucosan in atmospheric fine particles were analyzed. The main sources of organic aerosols were identified by molecular markers, diagnostic ratios, and a principal component analysis-multiple liner regression (PCA-MLR) model. The results showed that the average mass concentration of PM2.5 was (79.0±55.7) µg·m-3, and the averaged OC and EC mass concentrations were (20.7±15.6) µg·m-3 and (2.2±1.1) µg·m-3, which accounted for 26.2% and 2.8% of PM2.5, respectively. The total average concentration of the tested non-polar organic compounds was (186.3±104.5) ng·m-3 and, in descending order, this was composed of n-alkane (101.3±67.0) ng·m-3, polycyclic aromatic hydrocarbons (81.4±46.0) ng·m-3, hopanes (3.8±1.9) ng·m-3. The PCA-MLR model results showed that the relative contributions of the main sources of organic aerosols were coal combustion (47.0%), biomass burning (42.6%), and traffic emission (10.4%).