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Abstract Oxygenated volatile organic compounds (OVOCs) are important precursors and products of atmospheric secondary pollution. The sources of OVOCs, however, are still quite uncertain, especially in the atmosphere with much pollution in China. To study the sources of OVOCs in rural atmospheres, a proton transfer reaction mass spectrometry (PTR-MS) was deployed at a northern rural site (WD) and a southern rural site (YMK) in China during the summer of 2014 and 2016, respectively. The continuous observation showed that the mean concentration of TVOCs (totally 17 VOCs) measured at WD (52.4 ppbv) was far higher than that at YMK (11.1 ppbv), and the OVOCs were the most abundant at both the two sites. The diurnal variations showed that local sources of OVOCs were still prominent at WD, while regional transport influenced YMK much. The photochemical age-based parameterization method was then used to quantitatively apportion the sources of ambient OVOCs. The anthropogenic primary sources at WD and YMK contributed less (2%–16%) to each OVOC species. At both the sites, the atmospheric background had a dominant contribution (~ 50%) to acetone and formic acid, while the anthropogenic secondary formation was the main source (~ 40%) of methanol and MEK. For acetaldehyde and acetic acid, the biogenic sources were their largest source (~ 40%) at WD, while the background (39%) and anthropogenic secondary formation (42%) were their largest sources at YMK, respectively. This study reveals the complexity of sources of OVOCs in China, which urgently needs explored further. Graphical abstract Based on the photochemical age-based parameterization method for assessing the relative contribution of different sources of OVOCs, the anthropogenic primary sources at WD and YMK contributed less to each OVOC species. Unlabelled Image [ABSTRACT FROM AUTHOR]

Water-soluble organic matter (WSOM) represents a critical fraction of fine particles (PM 2.5 ) in the air, but its changing behaviors and formation mechanisms are not well understood yet, partly due to the lack of fast techniques for the ambient measurements. In this study, a novel system for the on-line measurement of water-soluble components in PM 2.5 , the particle-into-liquid sampler (PILS)–Nebulizer–aerosol chemical speciation monitor (ACSM), was developed by combining a PILS, a nebulizer, and an ACSM. High time resolution concentrations of WSOM, sulfate, nitrate, ammonium, and chloride, as well as mass spectra, can be obtained with satisfied quality control results. The system was firstly applied in China for field measurement of WSOM. The mass spectrum of WSOM was found to resemble that of oxygenated organic aerosol, and WSOM agreed well with secondary inorganic ions. All evidence collected in the field campaign demonstrated that WSOM could be a good surrogate of secondary organic aerosol (SOA). The PILS–Nebulizer–ACSM system can thus be a useful tool for intensive study of WSOM and SOA in PM 2.5 . [ABSTRACT FROM AUTHOR]

Knowledge of particle number size distribution (PND) and new particle formation (NPF) events in Southern China is essential for mitigation strategies related to submicron particles and their effects on regional air quality, haze, and human health. In this study, seven field measurement campaigns were conducted from December 2013 to May 2015 using a scanning mobility particle sizer (SMPS) at four sites in Southern China, including three urban sites and one background site. Particles were measured in the size range of 15–615 nm, and the median particle number concentrations (PNCs) were found to vary in the range of 0.3 × 10 4 –2.2 × 10 4 cm − 3 at the urban sites and were approximately 0.2 × 10 4 cm − 3 at the background site. The peak diameters at the different sites varied largely from 22 to 102 nm. The PNCs in the Aitken mode (25–100 nm) at the urban sites were up to 10 times higher than they were at the background site, indicating large primary emissions from traffic at the urban sites. The diurnal variations of PNCs were significantly influenced by both rush hour traffic at the urban sites and NPF events. The frequencies of NPF events at the different sites were 0%–30%, with the highest frequency occurring at an urban site during autumn. With higher SO 2 concentrations and higher ambient temperatures being necessary, NPF at the urban site was found to be more influenced by atmospheric oxidizing capability, while NPF at the background site was limited by the condensation sink. This study provides a unique dataset of particle number and size information in various environments in Southern China, which can help understand the sources, formation, and the climate forcing of aerosols in this quickly developing region, as well as help constrain and validate NPF modeling. [ABSTRACT FROM AUTHOR]

• Size-resolved Effective density of submicron atmospheric particles in Shenzhen were measured online using DMA-CPMA-CPC combined system. • Bimodal distribution feature of particle effective density was identified, including a main density mode and a sub density mode, by bimodal Gaussian fitting. • Particle effective density exhibited a high occurrence frequency of bimodal distribution, and two density modes exhibited opposite size distribution trends. • Effective density variation was highly correlated with the proportion of OA, sulfates and BC. Effective density (ρ eff) is one of the most important physical properties of atmospheric particles, providing important references in exploring the emissions and aging processes of fresh particles. In this study, a combined system of differential mobility analyzer, centrifugal particle mass analyzer, and condensation particle counter was used to periodically measure the ρ eff of atmospheric particles in Shenzhen from Oct. 2021 to Jan. 2022. Results showed that the ρ eff of particles with various size presented a bimodal distribution, which could be divided into main density (ρ m , main peak, corresponding to relatively dense particles after aging) and sub density (ρ s , sub peak, corresponding to fresh particles). The occurrence frequencies of ρ s of particles with diameters of 50 and 80 nm were less than 20%, but were as high as about 40% of that with diameters from 120 to 350 nm. The ρ m showed increasing trend with the size of particles, while ρ s decreased as the increasing of the size of particles. The ρ eff on pollution day varied significantly with chemical compositions. The increasing of the proportion of sulfate could promote the increasing of ρ eff , while black carbon and organic matter caused opposite effects, which may be related to various factors, including the difference of the material density and morphology of various chemical components. The ρ eff of 50, 80 and 120 nm particles decreased considerably during the new particle formation event, indicating that organic condensation was an important contributor to new particle growth. [ABSTRACT FROM AUTHOR]

Haze in China is primarily caused by high pollution of atmospheric fine particulates (PM 2.5 ). However, the detailed source structures of PM 2.5 light extinction have not been well established, especially for the roles of various organic aerosols, which makes haze management lack specified targets. This study obtained the mass concentrations of the chemical compositions and the light extinction coefficients of fine particles in the winter in Dongguan, Guangdong Province, using high time resolution aerosol observation instruments. We combined the positive matrix factor (PMF) analysis model of organic aerosols and the multiple linear regression method to establish a quantitative relationship model between the main chemical components, in particular the different sources of organic aerosols and the extinction coefficients of fine particles with a high goodness of fit ( R 2 = 0.953). The results show that the contribution rates of ammonium sulphate, ammonium nitrate, biomass burning organic aerosol (BBOA), secondary organic aerosol (SOA) and black carbon (BC) were 48.1%, 20.7%, 15.0%, 10.6%, and 5.6%, respectively. It can be seen that the contribution of the secondary aerosols is much higher than that of the primary aerosols (79.4% versus 20.6%) and are a major factor in the visibility decline. BBOA is found to have a high visibility destroying potential, with a high mass extinction coefficient, and was the largest contributor during some high pollution periods. A more detailed analysis indicates that the contribution of the enhanced absorption caused by BC mixing state was approximately 37.7% of the total particle absorption and should not be neglected. [ABSTRACT FROM AUTHOR]

Taiwan Strait is a special channel for subtropical East Asian Monsoon and its western coast is an important economic zone in China. In this study, a suburban site in the city of Xiamen on the western coast of Taiwan Strait was selected for fine aerosol study to improve the understanding of air pollution sources in this region. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and an Aethalometer were deployed to measure fine aerosol composition with a time resolution of 5 min from May 1 to 18, 2015. The average mass concentration of PM1 was 46.2 ± 26.3 μg/m3 for the entire campaign. Organics (28.3%), sulfate (24.9%), and nitrate (20.6%) were the major components in the fine particles, followed by ammonium, black carbon (BC), and chloride. Evolution of nitrate concentration and size distribution indicated that local NOx emissions played a key role in high fine particle pollution in Xiamen. In addition, organic nitrate was found to account for 9.0%–13.8% of the total measured nitrate. Positive Matrix Factorization (PMF) conducted with high-resolution organic mass spectra dataset differentiated the organic aerosol into three components, including a hydrocarbon-like organic aerosol (HOA) and two oxygenated organic aerosols (SV-OOA and LV-OOA), which on average accounted for 27.6%, 28.8%, and 43.6% of the total organic mass, respectively. The relationship between the mass concentration of submicron particle species and wind further confirmed that all major fine particle species were influenced by both strong local emissions in the southeastern area of Xiamen and regional transport through the Taiwan Strait. [ABSTRACT FROM AUTHOR]

Herein, we use an oxidation flow reactor, Gothenburg: Potential Aerosol Mass (Go: PAM) reactor, to investigate the secondary organic aerosol (SOA) formation from wheat straw burning. Biomass burning emissions are exposed to high concentrations of hydroxyl radicals (OH) to simulate processes equivalent to atmospheric oxidation of 0-2.55 days. Primary volatile organic compounds (VOCs) were investigated, and particles were measured before and after the Go: PAM reactor. The influence of water content (i.e. 5% and 11%) in wheat straw was also explored. Two burning stages, the flaming stage, and non-flaming stages, were identified. Primary particle emission factors (EFs) at a water content of 11% (∼3.89 g/kg-fuel) are significantly higher than those at a water content of 5% (∼2.26 g/kg-fuel) during the flaming stage. However, the water content showed no significant influence at the non-flaming stage. EFs of aromatics at a non-flaming stage (321.8±46.2 mg/kg-fuel) are larger than that at a flaming stage (130.9±37.1 mg/kg-fuel). The OA enhancement ratios increased with the increase in OH exposure at first and decreased with the additional increment of OH exposure. The maximum OA enhancement ratio is ∼12 during the non-flaming stages, which is much higher than ∼ 1.7 during the flaming stages. The mass spectrum of the primary wheat burning organic aerosols closely resembles that of resolved biomass burning organic aerosols (BBOA) based on measurements in ambient air. Our results show that large gap (∼60%-90%) still remains to estimate biomass burning SOA if only the oxidation of VOCs were included. [Display omitted]. [ABSTRACT FROM AUTHOR]

Abstract Oxygenated volatile organic compounds (OVOCs) are key intermediates in the atmospheric photooxidation process. To further study the primary and secondary sources of OVOCs, their ambient levels were monitored using a proton-transfer reaction mass spectrometer (PTR-MS) at an urban site in the Pearl River Delta of China. Continuous monitoring campaigns were conducted in the spring, summer, fall, and winter of 2016. Among the six types of OVOC species, the mean concentrations of methanol were the highest in each season (up to 13–20 ppbv), followed by those of acetone, acetaldehyde and acetic acid (approximately 2–4 ppbv), while those of formic acid and methyl ethyl ketone (MEK) were the lowest (approximately 1–2 ppbv). As observed from a diurnal variation chart, the OVOCs observed in Shenzhen may have been affected by numerous factors such as their primary and secondary sources and photochemical consumption. The photochemical age-based parameterization method was used to apportion the sources of ambient OVOCs. Methanol had significant anthropogenic primary sources but negligible anthropogenic secondary sources during all of the seasons. Acetone, MEK and acetic acid were mostly attributed to anthropogenic primary sources during each season with smaller contributions from anthropogenic secondary sources. Acetaldehyde had similar contributions from both anthropogenic secondary and anthropogenic primary sources throughout the year. Meanwhile, anthropogenic primary sources contributed the most to formic acid. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]