Observation on the aerosol and ozone precursors in suburban areas of Shenzhen and analysis of potential source based on MAX-DOAS

Long-term stereoscopic observations of aerosol, NO₂, and HCHO were carried out at the Yangmeikeng (YMK) site in Shenzhen. Aerosol optical depths and NO₂ vertical column concentration (NO₂ VCD) derived from MAX-DOAS were found to be consistent with other datasets. The total NO₂ VCD values of the site remained low, varying from 2 × 10¹⁵ to 8 × 10¹⁵ mol/cm², while the HCHO VCD was higher than NO₂ VCD, varying from 7 × 10¹⁵ to 11 × 10¹⁵ mol/cm². HCHO VCD was higher from September to early November than that was from mid-late November to December and during February 2021, in contrast, NO₂ VCD did not change much during the same period. In January, NO₂ VCD and HCHO VCD were both fluctuating drastically. High temperature and HCHO level in the YMK site is not only driving the ozone production up but also may be driving up the ozone concentration as well, and the O₃ production regime in the YMK site tends to be NO_x-limited. At various altitudes, backward trajectory clustering analysis and Potential Source Contribution Function (PSCF) were utilized to identify possible NO₂ and HCHO source locations. The results suggested that the Huizhou-Shanwei border and the Daya Bay Sea area were the key potential source locations in the lower (200 m) and middle (500 m) atmosphere (WPSCF > 0.6). The WPSCF value was high at the 1000 m altitude which was closer to the YMK site than the near ground, indicating that the pollution transport capability in the upper atmosphere was limited.

Source apportionment of PM2.5 in Seoul, South Korea and Beijing, China using dispersion normalized PMF

East Asian countries experience severe air pollution owing to their rapid development and urbanization induced by substantial economic activities. South Korea and China are among the most polluted East Asian countries with high mass concentrations of PM_2.5. Although the occurrence of transboundary air pollution among neighboring countries has been recognized for a long time, studies involving simultaneous ground-based PM_2.5 monitoring and source apportionment in South Korea and China have not been conducted to date. This study performed simultaneous daily ground-based monitoring of PM_2.5 in Seoul and Beijing from January to December 2019. The mass concentrations of PM_2.5 and its major chemical components were analyzed simultaneously during 2019. Positive matrix factorization (PMF) as well as dispersion normalized PMF (DN-PMF) were utilized for the source apportionment of ambient PM_2.5 at the two sites. 23 h average ventilation coefficients were applied for daily PM_2.5 chemical constituents' data. Nine sources were identified at both sites. While secondary nitrate, secondary sulfate, mobile, oil combustion, biomass burning, soil, and aged sea salt were commonly found at both sites, industry/coal combustion and incinerator were identified only at Seoul and incinerator/industry and coal combustion were identified only at Beijing. Reduction of the meteorological influences were found in DN-PMF compare to C-PMF but the effects of DN on mobile source were reduced by averaging over the 23 h sampling period. The DN-PMF results showed that Secondary nitrate (Seoul: 25.5%; Beijing: 31.7%) and secondary sulfate (Seoul: 20.5%; Beijing: 17.6%) were most dominant contributors to PM_2.5 at both sites. Decreasing secondary sulfate contributions and increasing secondary nitrate contributions were observed at both sites.

Environmental impact and health risk assessment of volatile organic compound emissions during different seasons in Beijing

Volatile organic compounds (VOCs) are major contributors to air pollution. Based on the emission characteristics of 99 VOCs that daily measured at 10 am in winter from 15 December 2015 to 17 January 2016 and in summer from 21 July to 25 August 2016 in Beijing, the environmental impact and health risk of VOC were assessed. In the winter polluted days, the secondary organic aerosol formation potential (SOAP) of VOC (199.70 ± 15.05 μg/m³) was significantly higher than that on other days. And aromatics were the primary contributor (98.03%) to the SOAP during the observation period. Additionally, the result of the ozone formation potential (OFP) showed that ethylene contributed the most to OFP in winter (26.00% and 27.64% on the normal and polluted days). In summer, however, acetaldehyde was the primary contributor to OFP (22.00% and 21.61% on the normal and polluted days). Simultaneously, study showed that hazard ratios and lifetime cancer risk values of acrolein, chloroform, benzene, 1,2-dichloroethane, acetaldehyde and 1,3-butadiene exceeded the thresholds established by USEPA, thereby presenting a health risk to the residents. Besides, the ratio of toluene-to-benzene indicated that vehicle exhausts were the main source of VOC pollution in Beijing. The ratio of m-/p-xylene-to-ethylbenzene demonstrated that there were more prominent atmospheric photochemical reactions in summer than that in winter. Finally, according to the potential source contribution function (PSCF) results, compared with local pollution sources, the spread of pollution from long-distance VOCs had a greater impact on Beijing.

Characteristics and formation mechanism of persistent extreme haze pollution events in Chengdu, southwestern China

Extreme PM_2.5 and nonmethane hydrocarbon (NMHC) pollution often occurs simultaneously during the winter. To study the formation mechanism of two pollution events in Chengdu from 23 December 2016 to 31 January 2017, we explored the weather conditions, chemical composition, secondary pollutant conversion, aerosol hygroscopic growth, and potential source contribution function (PSCF) during this period. During the study period, the humidity was high (67.9%), the wind speed was low (1.0 m s^-1), the height of the planetary boundary layer was low (463.4 m), and the atmosphere remained stationary. The potential source regions of PM_2.5 and NMHCs were locally polluted sites in the southwestern and southern regions of Chengdu, affected by the southwesterly air mass trajectories. PM_2.5 and sulfur oxidation ratios (SOR), nitrogen oxidation ratios (NOR) and secondary organic aerosol formation potential (SOAP) showed a strong positive correlation. As pollution increased, the conversion from SO₂, NO_x and NMHCs to sulfate, nitrate and SOAs increased, resulting in an increase in the secondary aerosol concentration. As the relative humidity increases, aerosols begin to undergo rapid hygroscopic growth, which seriously affects the visibility of the atmosphere. In general, pollutant emissions, static weather, and secondary conversion, among other factors, lead to the occurrence of this persistent extreme haze pollution.

Comparison of ionic and carbonaceous compositions of PM2.5 in 2009 and 2012 in Shanghai, China

Daily PM2.5 samples were obtained at the site of East China University of Science and Technology (ECUST) in urban Shanghai during 2009-2010 and 2011-2012. The temporal variations of PM2.5 and its chemical compositions including secondary inorganic aerosol (SIA) and carbonaceous components were studied. The concentrations of PM2.5 were (94.04±52.17) μg/m3 and (68.44±41.57) μg/m3 in 2009 and 2012, respectively. The concentrations and contributions of SIA to PM2.5 were significantly higher in 2012 than those in 2009. Sulfate took up above 50% of SIA in 2009 and the corresponding value decreased to 41% in 2012. The increasing trend of NO3-/SO4(2-) mass ratio implied that the contributions of mobile sources were more and more important. The molar ratios of [NH4+]/(2[SO4(2-)]+[NO3-]) were 0.57 and 0.70, lower than 1, which demonstrated that most aerosol samples were ammonium-poor. But the neutralization process of ammonium might affect the formation of sulfate and nitrate, which was indicated by the strong correlation between [NH4+]-[SO4(2-)] and [NH4+]-[NO3-]. The average molar ratio of ammonium to sulfate was 1.74 in 2009, so there was not enough ammonium to neutralize sulfate sufficiently. The higher value of 2.30 in 2012 indicated that sulfate was sufficiently neutralized by ammonium and the predominant production was (NH4)2SO4. Aerosol samples had higher char-EC/soot-EC ratios and lower OC/EC ratios in 2009 than those of samples in 2012. The higher K+/OC values demonstrated that biomass burning made important contributions to carbonaceous components in both 2009 and 2012. All backward trajectories were grouped into four clusters, mainly from the Northwest, the Circum-Bohai-Sea Region (CBSR), the Southwest and the Southeast. The cluster from the Northwest was the most polluted pathway in 2009, while the cluster from the CBSR had more effects in 2012. PSCF model for PM2.5 and carbonaceous components except soot-EC suggested that the Yangtze River Delta Region (YRDR) made significant contributions by short-range transportation in 2009 and 2012. The Northwest, the CBSR and the Pearl River Delta Region (PRDR) were also the potential source areas. However, the source pattern of soot-EC was significantly different from those of other carbonaceous components.