Links between the optical properties and chemical compositions of brown carbon (BrC) are poorly understood because of the complexity of BrC chromophores. We conducted field studies simultaneously at both vehicle-influenced site and biomass burning-affected site in China in polluted winter. The chemical compositions and light absorption values of functionalized aromatic compounds, including phenyl aldehyde, phenyl acid, and nitroaromatic compounds, were measured. P-phthalic acid, nitrophenols and nitrocatechols were dominant BrC species, accounting for over 50% of the concentration of identified chromophores. Nitrophenols and nitrocatechols contributed more than 50% of the identified BrC absorbance between 300 and 400 nm. Oxidation of biomass burning-related products (e.g., pyrocatechol and methylcatechols) and anthropogenic volatile organic compounds (e.g., benzene and toluene) generated similar BrC chromophores, implying that these functionalized aromatic compounds play an important role in both environments. Compared with the biomass burning-affected site (22%), functionalized aromatic compounds at vehicle-influenced site accounted for a higher percentage of BrC absorption (25%). This research improves our understanding of the links between optical properties and composition of BrC, and the difference between BrC chromophores from BB-influenced area and vehicle-affected area under polluted atmospheric conditions. © 2021 Elsevier B.V.

Particulate PAHs are of significant concern due to their carcinogenic and mutagenic properties. In order to investigate the characteristics and sources of particulate PAHs during heavy pollution episodes, PM2.5 samples were collected in Beijing and Dezhou in the North China Plain from November 17th, 2018 to January 19th, 2019. 26 species of PAHs in PM2.5 during six heavy pollution episodes were measured by gas chromatography-mass spectrometer (GC-MS). The results showed that: (1) The total concentration of PAHs during six heavy pollution episodes ranged from 62 to 191 ng/m3 in Dezhou, and from 61 to 129 ng/m3 in Beijing. (2) The ratios of ∑26PAHs/PM2.5 were higher in Beijing, although PM2.5 concentrations were lower. (3) The dominant components of PAHs were benzo[b]fluoranthene, benzo[a]pyrene (Bap), benzo[a]anthracene, methyl-fluoranthene and retene, accounting for about 50% of ∑26PAHs. (4) The diagnostic ratios indicated vehicle exhaust, coal combustion and biomass burning were the main sources of PAHs at both sites. A more obvious influence of biomass burning in Dezhou was found via a tracer-based approach and using the ratio of PAHs to levoglucosan in fresh biomass burning aerosols. (5) The Bap toxic equivalent concentrations (TEQ) were 6.5-17.2 ng/m3, with higher values in Dezhou than those in Beijing. The BaP concentration ranged from 5.2 to 13.1 ng/m3 and exceeded BaP standard (24 h average: 2.5 ng/m3) in China (Ambient Air Quality Standard, GB 3095-2012), indicating a potential hazardous effect on human health. The studies have shown that both sites have similar distribution characteristics and sources, while the enrichment ratios of ∑26PAHs/PM2.5 in Beijing were higher. PAHs emission control needs to be further strengthened to reduce the risk of human exposure to heavy pollution episodes and the PM2.5 pollution levels. © 2021, Editorial Board, Research of Environmental Sciences. All right reserved.

A source-oriented Community Multiscale Air Quality model was used to quantify the contributions of different sources to ground-level fine particulate matter (PM2.5) and ozone (O3) over the Yangtze River Delta (YRD) region during the EXPLORE-YRD (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation, and their Effects in the Yangtze River Delta) campaign (17 May to June 17, 2018). O3 formation in most urban areas of YRD is attributed to volatile organic compounds (VOCs) (81.1%, 78.5%, 60.2%, and 55.1% in Shanghai, Nanjing, Hefei, and Hangzhou, respectively), but is affected more by nitrogen oxides (NOx) in suburban and rural areas. Industry and transportation are the two major sources of O3 and PM2.5. In addition to the two sources, NOx produced owing to power generation, and VOC emissions from biogenic sources are important source of O3. Industry contributes the most to the total mass of PM2.5 in the YRD during the study period (9–25 μg/m3), followed by transportation (2–7 μg/m3). Industry, residential emissions, and transportation are the major sources of primary organic carbon and elemental carbon, whereas industry, transportation, and power generation account for most of the sulphate (SO2− 4) and nitrate (NO− 3) in the YRD. Agriculture is the most dominant source of ammonium emissions (NH+ 4). In Shanghai, Nanjing, Hefei, and Taizhou, secondary organic aerosol (SOA) are mainly contributed by industrial emissions. However, in Hangzhou, biogenic emissions contribute more than 40% of SOA. During all types of pollution episodes, industry and transportation are generally the two greatest sources of O3 and PM2.5 in YRD. The contribution of industry is higher during high PM2.5 pollution episodes, whereas biogenic and open burning contributions are more important during high O3 episodes. Overall, anthropogenic sources dominate the formation of O3 and PM2.5 pollution in the YRD, whereas biogenic emissions contribute significantly to O3 attributable to VOC emissions (O3_VOCs) accounting for 9–20% in urban areas of the YRD. © 2021 Elsevier Ltd

Severe haze pollution occurs frequently in the winter over the Beijing-Tianjin-Hebei (BTH) region (China), exerting profound impacts on air quality, visibility, and human health. The Chinese Government has taken strict mitigation actions since 2013 and has achieved a significant reduction in the annual mean PM2.5 concentration over this region. However, the level of secondary aerosols during heavy haze episodes showed little decrease during this period. During heavy haze episodes, the concentrations of secondary aerosol components, including sulfate, nitrate and secondary organics, in aerosol particles increase sharply, acting as the main contributors to aerosol pollution. To achieve effective control of particle pollution in the BTH region, the precise and complete secondary aerosol formation mechanisms have been investigated, and advances have been made about the mechanisms of gas phase reaction, nucleation and heterogeneous reactions in forming secondary aerosols. This paper reviews the research progress in aerosol chemistry during haze pollution episodes in the BTH region, lays out the challenges in haze formation studies, and provides implications and directions for future research. [Figure not available: see fulltext.]. © 2020, Higher Education Press.

Nitro-aromatic compounds (NACs) were measured hourly at a rural site in China during wintertime to monitor the changes due to local and regional impacts of biomass burning (BB). Concurrent and continuous measurements of the concentrations of 16 NACs in the gas and particle phases were performed with a time-of-flight chemical ionization mass spectrometer (CIMS) equipped with a Filter Inlet for Gases and AEROsols (FIGAERO) unit using iodide as the reagent ion. NACs accounted for <2% of the mass concentration of organic matter (OM) and total particulate matter (PM), but the total particle mass concentrations of these compounds can reach as high as 1000 ngm-3 (299 ngm-3 avg), suggesting that they may contribute significantly to the radiative forcing effects of atmospheric particles. Levels of gas-phase NACs were highest during the daytime (15:00-16:00 local time, LT), with a smaller nighttime peak around 20:00 LT. Box-model simulations showed that this occurred because the rate of NAC production from gas-phase sources exceeded the rate of loss, which occurred mainly via the OH reaction and to a lesser degree via photolysis. Data gathered during extended periods with high contributions from primary BB sources (resulting in 40 %-60% increases in NAC concentrations) were used to characterize individual NACs with respect to gas-particle partitioning and the contributions of regional secondary processes (i.e. photochemical smog). On days without extensive BB, secondary formation was the dominant source of NACs, and NAC levels correlated strongly with the ambient ozone concentration. Analyses of individual NACs in the regionally aged plumes sampled on these days allowed precursors such as phenol and catechol to be linked to their NAC derivatives (i.e. nitrophenol and nitrocatechol). Correlation analysis using the high time resolution data and box-model simulation results constrained the relationships between these compounds and demonstrated the contribution of secondary formation processes. Furthermore, 13 of 16 NACS were classified according to primary or secondary formation process. Primary emission was the dominant source (accounting for 60 %- 70% of the measured concentrations) of 5 of the 16 studied NACs, but secondary formation was also a significant source. Photochemical smog thus has important effects on brown carbon levels even during wintertime periods dominated by primary air pollution in rural China. © Author(s) 2021.

The phase states of primarily emitted and secondarily formed aerosols from gasoline vehicle exhausts were investigated by quantifying the particle rebound fraction (f). The rebound behaviors of gasoline vehicle emission-related aerosols varied with engines, fuel types, and photochemical aging time, showing distinguished differences from biogenic secondary organic aerosols. The nonliquid-to-liquid phase transition of primary aerosols emitted from port fuel injection (PFI) and gasoline direct injection (GDI) vehicles started at a relative humidity (RH) = 50 and 60%, and liquefaction was accomplished at 60 and 70%, respectively. The RH at which f declined to 0.5 decreased from 70 to 65% for the PFI case with 92# fuel, corresponding to the photochemical aging time from 0.37 to 4.62 days. For the GDI case, such RH enhanced from 60 to 65%. Our results can be used to imply the phase state of traffic-related aerosols and further understand their roles in urban atmospheric chemistry. Taking Beijing, China, as an example, traffic-related aerosols were mainly nonliquid during winter with the majority ambient RH below 50%, whereas they were mostly liquid during the morning rush hour of summer, and traffic-related secondary aerosols fluctuated between nonliquid and liquid during the daytime and tended to be liquid at night with increased ambient RH. © 2020 American Chemical Society.

In the present work, we performed chassis dynamometer experiments to investigate the emissions and secondary organic aerosol (SOA) formation potential of intermediate-volatility organic compounds (IVOCs) from an on-road Chinese gasoline vehicle. High IVOC emission factors (EFs) and distinct volatility distribution were recognized. The IVOC EFs for the China V vehicle ranged from 12.1 to 226.3 mg per kilogram fuel, with a median value of 83.7 mg per kilogram fuel, which was higher than that from US vehicles. Besides, a large discrepancy in volatility distribution and chemical composition of IVOCs from Chinese gasoline vehicle exhaust was discovered, with larger contributions of B14-B16 compounds (retention time bins corresponding to C14-C16 n-alkanes) and a higher percentage of n-alkanes. Further we investigated the possible reasons that influence the IVOC EFs and volatility distribution and found that fuel type, starting mode, operating cycles and acceleration rates did have an impact on the IVOC EF. When using E10 (ethanol volume ratio of 10 %, v=v) as fuel, the IVOC EF of the tested vehicle was lower than that using commercial China standard V fuel. The average IVOC-to-THC (total hydrocarbon) ratios for gasoline-fueled and E10-fueled gasoline vehicles were 0:07 ± 0:01 and 0:11 ± 0:02, respectively. Cold-start operation had higher IVOC EFs than hot-start operation. The China Light-Duty Vehicle Test Cycle (CLTC) produced 70 % higher IVOCs than those from the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). We found that the tested vehicle emitted more IVOCs at lower acceleration rates, which leads to high EFs under CLTC. The only factor that may influence the volatility distribution and compound composition is the engine aftertreatment system, which has compound and volatility selectivity in exhaust purification. These distinct characteristics in EFs and volatility may result in higher SOA formation potential in China. Using published yield data and a surrogate equivalent method, we estimated SOA formation under different OA (organic aerosol) loading and NOx conditions. Results showed that under low-and high-NOx conditions at different OA loadings, IVOCs contributed more than 80 % of the predicted SOA. Furthermore, we built up a parameterization method to simply estimate the vehicular SOA based on our bottomup measurement of VOCs (volatile organic compounds) and IVOCs, which would provide another dimension of information when considering the vehicular contribution to the ambient OA. Our results indicate that vehicular IVOCs contribute significantly to SOA, implying the importance of reducing IVOCs when making air pollution controlling policies in urban areas of China. © 2021 Author(s).

During the COVID-19 lockdown in 2020, large-scale industrial and transportation emissions were reduced, but high PM2.5 concentration still occurred. This study investigated the variation of particle number size distribution during the lockdown, and analyzed the characteristics of new particle formation (NPF) events and its potential impact on haze formation. Through measurement conducted in urban Beijing during the first 3 months of 2020, and comparison with year-over-year data, the decrease of primary Aitken-mode particles was observed. However, frequencies, formation rates and growth rates of NPF events remained stable between 2020 and 2019 in the same period. As a result, &gt;25 nm particles produced by NPF events, would play a more important role in serving as the haze formation “seeds” compared to those produced by primary emissions. This finding emphasizes the significance on the understanding of NPF mechanisms when making pollution mitigation policy in the future. © 2021. The Authors.

To investigate the composition, variation, and sources of nitrated phenols (NPs) in the winter of Beijing, gas-phase NPs were measured by a chemical ionization long time-of-flight mass spectrometer (CI-LToF-MS). A box model was applied to simulate the secondary formation process of NPs. In addition, the primary sources of NPs were resolved by a non-negative matrix factorization (NMF) model. Our results showed that secondary formation contributed 38 %, 9 %, 5 %, 17 %, and almost 100% of the nitrophenol (NP), methyl-nitrophenol (MNP), dinitrophenol (DNP), methyl-dinitrophenol (MDNP or DNOC), and dimethyl-nitrophenol (DMNP) concentrations. The phenol-OH reaction was the predominant loss pathway (46.7 %) during the heavy pollution episode, which produced the phenoxy radical (C6H5O). The phenoxy radical consequently reacted with NO2 and produced nitrophenol. By estimating the primarily emitted phenol from the ratio of phenol=CO from freshly emitted vehicle exhaust, this study proposed that oxidation of primary phenol contributes much more nitrophenol (37 %) than that from benzene oxidation (< 1 %) in the winter of Beijing. The latter pathway was widely used in models and might lead to great uncertainties. The source apportionment results by NMF indicated the importance of combustion sources (> 50 %) to the gas-phase NPs. The industry source contributed 30% and 9% to DNP and MDNP, respectively, which was non-negligible. The concentration weighted trajectory (CWT) analysis demonstrated that regional transport from provinces that surround the Yellow and Bohai seas contributed more primary NPs to Beijing. Both primary sources and secondary formation at either local or regional scale should be considered when making control policies of NPs. © 2021 Kai Song et al.

To investigate the regional secondary organic aerosol (SOA) formation at Yangtze River Delta (YRD) region, China, the chemical composition of fine particles and their gaseous precursors were simultaneously measured at a regional site, Taizhou, during EXPeriment on the eLucidation of the atmospheric Oxidation capacity, aerosol foRmation and their Effects in Yangtze River Delta (EXPLORE-YRD) intensive field campaign from May to June 2018. Secondary organic carbon (SOC) was estimated by both bottom-up and top-down method, i.e. the yield method from volatile organic compounds (VOCs) oxidation, and the elemental carbon (EC) tracer method. Our result showed that the oxidation of alkanes and aromatics measured by GC-MS/FID based on the yield method could only explain 25.3% of the SOC derived from the EC tracer method, in which aromatics were the dominant contributors (23.9%). This percentage increased to 39.5% while two semi-volatile organic compounds (SVOCs), i.e. naphthalene, and methylnaphthalene, were used in the calculation, suggesting the importance of SVOCs on SOA formation. The SOA formation pathways were further explored. The good correlation of SOC and odd oxygen (Ox) indicated the important role of photochemical reactions on SOA formation in the summer of YRD. Our findings evaluated the contributions of VOCs to SOA formation in Taizhou, revealed the importance of SVOCs to SOA formation and highlighted an urgent need for more exploration of SVOCs in the future. © 2020 The Authors