Underestimation of biomass burning contribution to PM2.5 due to its chemical degradation based on hourly measurements of organic tracers: A case study in the Yangtze River Delta (YRD) region, China.

Biomass burning (BB) has significant impacts on air quality and climate change, especially during harvest seasons. In previous studies, levoglucosan was frequently used for the calculation of BB contribution to PM2.5, however, the degradation of levoglucosan (Lev) could lead to large uncertainties. To quantify the influence of the degradation of Lev on the contribution of BB to PM2.5, PM2.5-bound biomass burning-derived markers were measured in Changzhou from November 2020 to March 2021 using the thermal desorption aerosol gas chromatography-mass spectrometry (TAG-GC/MS) system. Temporal variations of three anhydro-sugar BB tracers (e.g., levoglucosan, mannosan (Man), and galactosan (Gal)) were obtained. During the sampling period, the degradation level of air mass (x) was 0.13, indicating that ~87 % of levoglucosan had degraded before sampling in Changzhou. Without considering the degradation of levoglucosan in the atmosphere, the contribution of BB to OC were 7.8 %, 10.2 %, and 9.3 % in the clean period, BB period, and whole period, respectively, which were 2.4-2.6 times lower than those (20.8 %-25.9 %) considered levoglucosan degradation. This illustrated that the relative contribution of BB to OC could be underestimated (~14.9 %) without considering degradation of levoglucosan. Compared to the traditional method (i.e., only using K+ as BB tracer), organic tracers (Lev, Man, Gal) were put into the Positive Matrix Factorization (PMF) model in this study. With the addition of BB organic tracers and replaced K+ with K+BB (the water-soluble potassium produced by biomass burning), the overall contribution of BB to PM2.5 was enhanced by 3.2 % after accounting for levoglucosan degradation based on the PMF analysis. This study provides useful information to better understand the effect of biomass burning on the air quality in the Yangtze River Delta region.

Highly time-resolved measurements of elements in PM2.5 in Changzhou, China: Temporal variation, source identification and health risks.

The temporal variation, sources, and health risks of elemental composition in fine particles (PM2.5) were explored using online measurements of 19 elements with a time resolution of 1 h at an urban location in Changzhou, China, from December 10, 2020 to March 31, 2021. The mass concentration of PM2.5 was 50.1 ±â€¯32.6 µg m-3, with a range of 3-218 µg m-3. The total concentration of 19 elements (2568 ±â€¯1839 ng m-3) accounted for 5.1 % of PM2.5 mass concentration. S, Cl, Si, and Fe were the dominant elementary species, accounting for 90 % of total element mass concentrations during the whole campaign. Positive matrix factorization (PMF) model was applied to identify the major emission sources of elements in PM2.5. Seven factors, named secondary sulfate mixed with coal combustion, Cl-rich, traffic, iron and steel industry, soil dust, fireworks, and shipping, were identified. The major sources for elements were iron and steel industry, followed by soil dust and secondary sulfate mixed with coal combustion, explaining 32.0 %, 23.5 % and 16.7 % of the total source contribution, respectively. The total hazard index (HI) of elements was 3.01 for children and 1.18 for adults, much greater than the admissible level (HI = 1). The total carcinogenic risk (CR) in Changzhou was estimated to be 5.87 × 10-5, which was above the acceptable CR level (1 × 10-6). Among the calculated metal elements, Cr, Co and As have higher carcinogenic risk, and Co was found to trigger the highest noncarcinogenic risk to Children. Our results indicate that industrial emission is the dominant CR contributor, emphasizing the necessity for stringent regulation of industry sources. Overall, our study provides useful information for policymakers to reduce emissions and health risks from elements in the Yangtze River Delta region.

Hourly measurement of PM2.5-bound nonpolar organic compounds in Shanghai: Characteristics, sources and health risk assessment.

Fine particulate matter (PM2.5)-bound nonpolar organic compounds (NPOCs), including polycyclic aromatic hydrocarbons (PAHs) and alkanes, are commonly used as typical molecular markers for detailed source identification. Online thermal desorption aerosol gas chromatography-mass spectrometry (TAG) system can obtain ambient data with hourly resolution, which is of great importance for investigating the diurnal characteristics and refined source identification of NPOCs. From June to October 2020, hourly ambient aerosol samples were collected and analyzed to investigate the characteristics and sources of 14 PAHs and 15 alkanes (C21-C35) in PM2.5 using TAG at a suburban site of Baoshan district in Shanghai, China. The average concentration of summed PAHs and alkanes during the sampling period was 1.27 ± 1.4 ng/m3 and 8.87 ± 3.46 ng/m3, respectively, in which Benzo[b]fluoranthene (BbF), Benzo[ghi]perylene (BghiP) and Indeno[1,2,3-cd]pyrene (IcdP) are the dominant PAHs species, with n-Heptacosane (C27), n-Nonacosane (C29) and n-Hentriacontane (C31) being the most abundant n-alkane species. Carbon preference index (CPI) and carbon maximum (Cmax) number indicated that the sources of alkanes shifted from biogenic-oriented (such as plant wax) in the summer to anthropogenic-dominated (such as fossil fuels) in the autumn. Results from trajectory cluster analysis and potential source contribution function (PSCF) modeling showed that alkanes were mainly from the middle and lower reaches of the Yangtze River Plain including Anhui, Jiangxi, and Zhejiang provinces, while PAHs were mainly from northeastern China. Positive Matrix Factorization (PMF) model results indicated that gasoline (41.48%) and diesel (21.82%) were the two major sources of PM2.5-bound PAHs in summer and fall of 2020 in Shanghai, followed by coal consumption or catering (19.96%) and biomass burning (16.74%). Diurnal variation of PAHs sources resolved by PMF showed characteristic features consistent with the corresponding anthropogenic activities. For example, gasoline vehicle exhaust showed higher concentrations during traffic rush hours; while coal consumption or catering presented higher concentrations during lunch times from 10:00 to 12:00. In addition, the TAG data coupling with PMF also can be capable for source appointment of short-duration episodes. Health risk assessment showed that adult women were at greater lifetime cancer risk (ILCR) than people in other age groups, and people may subject to higher health risks at morning and night time. This work demonstrates that hourly NPOCs measured by TAG are uniquely specific on refined source identification and investigation into the characteristics of diurnal variations.