Primary emissions versus secondary formation of fine particulate matter in the most polluted city (Shijiazhuang) in North China

Abstract

Abstract. Particulate matter (PM) pollution is a severe environmental problem in the Beijing–Tianjin–Hebei (BTH) region in North China. PM studies have been conducted extensively in Beijing, but the chemical composition, sources, and atmospheric processes of PM are still relatively less known in nearby Tianjin and Hebei. In this study, fine PM in urban Shijiazhuang (the capital of Hebei Province) was characterized using an Aerodyne quadrupole aerosol chemical speciation monitor (Q-ACSM) from 11 January to 18 February in 2014. The average mass concentration of non-refractory submicron PM (diameter <1 µm, NR-PM1) was 178±101 µg m−3, and it was composed of 50 % organic aerosol (OA), 21 % sulfate, 12 % nitrate, 11 % ammonium, and 6 % chloride. Using the multilinear engine (ME-2) receptor model, five OA sources were identified and quantified, including hydrocarbon-like OA from vehicle emissions (HOA, 13 %), cooking OA (COA, 16 %), biomass burning OA (BBOA, 17 %), coal combustion OA (CCOA, 27 %), and oxygenated OA (OOA, 27 %). We found that secondary formation contributed substantially to PM in episodic events, whereas primary emissions were dominant (most significant) on average. The episodic events with the highest NR-PM1 mass range of 300–360 µg m−3 were comprised of 55 % of secondary species. On the contrary, a campaign-average low OOA fraction (27 %) in OA indicated the importance of primary emissions, and a low sulfur oxidation degree (FSO4) of 0.18 even at RH >90 % hinted at insufficient oxidation. These results suggested that in Shijiazhuang in wintertime fine PM was mostly from primary emissions without sufficient atmospheric aging, indicating opportunities for air quality improvement by mitigating direct emissions. In addition, secondary inorganic and organic (OOA) species dominated in pollution events with high-RH conditions, most likely due to enhanced aqueous-phase chemistry, whereas primary organic aerosol (POA) dominated in pollution events with low-RH and stagnant conditions. These results also highlighted the importance of meteorological conditions for PM pollution in this highly polluted city in North China.

Quantification of the impact of cooking processes on indoor concentrations of volatile organic species and primary and secondary organic aerosols

“…For example, emission rates from meat charbroiling are around 15 g kg −1 , three orders of magnitudes greater than those obtained here or reported for domestic cooking. The significantly higher emissions from commercial kitchens compared to domestic kitchens are also observed in the case of China, where COA is a prominent fraction of the aerosol in urban environments . This hypothesis is consistent with the observation of COA downwind of restaurants and during mobile measurements in restaurant areas .…”

A Black Carbon‐Tracer Method for Estimating Cooking Organic Aerosol From Aerosol Mass Spectrometer Measurements

“…COA is an important POA in urban environments worldwide (Figure ). The megacities in China and India showed much higher COA concentrations (4.8 ± 3.3 μg/m 3 ) than those in North America (1.4 ± 0.50 μg/m 3 ) and Europe (1.1 ± 0.50 μg/m 3 ), and the highest COA concentrations were observed in two most polluted cities, that is, Shijiazhuang, China (14.2 μg/m 3 ; Huang et al, ) and Kanpur, India (9 μg/m 3 ; Thamban et al, ). Although the COA concentrations varied spatially, the contributions to OA were relatively similar, which were 17.4 ± 5.6%, 20.2 ± 5.9%, and 15.4 ± 5.0% in Asia, North America, and Europe, respectively.…”

Summertime and wintertime atmospheric processes of secondary aerosol in Beijing

“…However, recent measurements of OH radicals at a suburban site in Beijing reported wintertime OH radical concentrations at noontime ranged from 2.4 × 10 6 cm −3 during severe pollution events (k OH ∼ 27 s −1 ) to 3.6 × 10 6 cm −3 during relatively clean events (k OH ∼ 5 s −1 ) (Tan et al, 2018). These OH radical concentrations are nearly an order of magnitude larger than those predicted by global models for northern China in winter (Lelieveld et al, 2016). The higher-thanexpected OH concentrations and moderate OH reactivity in Beijing resulted in fast photochemistry in winter (Lu et al, 2019), explaining the high contribution of secondary aerosol during wintertime severe haze events (Huang et al, 2014).…”

“…Compared to primary aerosol that is relatively well constrained in terms of the emission sources, secondary aerosol is still not well understood, likely due to its variable precursors, complex formation and atmospheric transformation processes mediated by meteorological conditions Petäjä et al, 2016;Tie et al, 2017;Xu et al, 2017). A number of studies have investigated the formation and aging processes of secondary aerosol (Takegawa et al, 2009;Huang et al, 2014Huang et al, , 2019Sun et al, 2014Sun et al, , 2016Wang et al, 2016;Duan et al, 2019). For example, field measurements showed that aqueous-phase oxidation of SO 2 could be an important formation pathway of sulfate at high RH during haze events Elser et al, 2016).…”

“…In particular, photochemical oxidation has been suggested to be the major pathway of SOA forma-tion during some pollution events in some cities (e.g., Beijing and Xi'an) because SOA correlated tightly with odd oxygen (O x ) and was independent of RH (e.g., Sun et al, 2014;Elser et al, 2016). However, aqueous-phase formation of SOA has also been considered an important pathway during some pollution events in, e.g., Beijing, Shijiazhuang and Baoji Wang et al, 2017;Huang et al, 2019). The formation of less-oxidized oxygenated OA (LO-OOA) and moreoxidized oxygenated OA (MO-OOA) in Baoji seemed to be significantly influenced by aqueous-phase chemistry during the period of low atmospheric oxidative capacity , while in another study Xu et al (2017) suggested that aqueous-phase processing has a dominant impact on MO-OOA formation but that photochemical oxidation is the dominant pathway for LO-OOA formation in Beijing.…”