Characterization and source apportionment of aerosol light scattering in a typical polluted city in the Yangtze River Delta, China

Abstract

Abstract. Through online observation and offline chemistry analysis of samples at suburban, urban and industrial sites (NJU, PAES and NUIST, respectively) in Nanjing, a typical polluted city in the Yangtze River Delta, we optimized the aerosol light scattering estimation method, identified its influencing factors and quantified the contributions of emission sources to aerosol scattering. The daily average concentration of PM2.5 during the sampling period (November 2015–March 2017) was 163.1±13.6 µg m−3 for the heavily polluted period, 3.8 and 1.6 times those for the clean (47.9±15.8 µg m−3) and lightly polluted (102.1±16.4 µg m−3) periods, respectively. The largest increase in PM concentration and its major chemical components was found at the size range of 0.56–1.0 µm for the heavily polluted period, and the contributions of nitrate and sulfate were the greatest in the 0.56–1.0 µm fraction (19.4 %–39.7 % and 18.1 %–34.7 %, respectively) for all the three periods. The results indicated that the large growth of nitrate and sulfate was one of the major reasons for the polluted periods. Based on measurements at the three sites, the US Interagency Monitoring of Protected Visual Environments (IMPROVE) algorithm was optimized to evaluate aerosol scattering in eastern China. The light absorption capacity of organic carbon (OC) was estimated to account for over half of the methanol-soluble organic carbon (MSOC) at NJU and PAES, whereas the fraction was lower at NUIST. Based on the Mie theory, we found that the high relative humidity (RH) could largely enhance the light scattering effect of accumulation particles, but it had few effects on the mixing state of particles. The scattering coefficients of particles within the 0.56–1.0 µm range contributed the most to the total scattering (28 %–69 %). The mass scattering efficiency (MSE) of sulfate and nitrate increased with the elevated pollution level, whereas a low MSE of organic matter (OM) was found for the heavily polluted period, probably because a proportion of OM had only a light absorption property. A coupled model of positive matrix factorization (PMF) and the Mie theory was developed and applied for the source apportionment of aerosol light scattering. Coal burning, industry and vehicles were identified as the major sources of the reduced visibility in Nanjing, with an estimated collective contribution at 64 %–70 %. The comparison between the clean and polluted period suggested that the increased primary particle emissions from vehicles and industry were the major causes of the visibility degradation in urban and industrial regions, respectively. In addition, secondary aerosols were a great contributor to the reduced visibility.

Shipborne Observations of Chemical Characterization and Light Extinction of Aerosol Along the Yangtze River, China

“…The source contributions of primary particles were obtained using the PMF model, and those of secondary inorganic aerosol (SIA) were further determined based on estimates of the nitrogen oxides (NO x ) and sulfur dioxide (SO 2 ) emissions in a local inventory. We followed the methods described in the PMF manual and Chen et al (2020) to calculate the chemical component uncertainties in the measurement dataset. Criteria including the optimum number of factors and the minimization of an objective function Q were determined based on the principles described in previous studies (Watson et al, 2015;Tian et al, 2016) and applied in the model to obtain the best PMF solution.…”

“…Criteria including the optimum number of factors and the minimization of an objective function Q were determined based on the principles described in previous studies (Watson et al, 2015;Tian et al, 2016) and applied in the model to obtain the best PMF solution. More details on the PMF solution were described in our previous study (Chen et al, 2020).…”

“…Wang et al (2016a) indicated that vehicle exhaust, secondary nitrate, and secondary sulfate were identified as the most significant sources for aerosol light extinction in Hangzhou. Chen et al (2020) suggested that the increased primary particle emissions from vehicles and industry were the major causes of the aerosol extinction in urban and industrial regions in Nanjing, respectively. Different from the urban regional studies (Li et al, 2014;Zhang et al, 2021), however, aerosol along the Yangtze River was largely affected by ship emissions (Li et al, 2018).…”

Development of a multiphase chemical mechanism to improve secondary organic aerosol formation in CAABA/MECCA (version 4.5.6-rc.1)

“…Secondary organic aerosol (SOA) is formed from anthropogenic and biogenic VOC in the atmosphere and comprises a significant amount of the total OA mass (Hallquist et al, 2009). Atmospheric aerosols have received increased attention in recent years, as a result of their impact on human health, urban visibility, and climate change (Lin et al, 2017;Chen et al, 2020;Zhong and Jang, 2011;Zhu et al, 2017). New SOA precursors, formation pathways, and loss reactions in the gas and the aqueous phase have been discovered (Wennberg et al, 2018;Hodzic et al, 2014;Lim et al, 2010).…”