Hourly measurement of PM_(2.5)-bound nonpolar organic compounds in Shanghai: Characteristics, sources and health risk assessment

摘要

Fine particulate matter (PM_(2.5))-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 (C_(21)-C_(35)) in PM_(2.5) 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/m~3 and 8.87 ± 3.46 ng/m~3, 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 (C_(max)) 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 PM_(2.5)-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.