Source characterization of urban particles from meat smoking activities in Chongqing, China using single particle aerosol mass spectrometry

Insights into the seasonal characteristics of single particle aerosols in Chengdu based on SPAMS

To investigate the seasonal characteristics in air pollution in Chengdu, a single particle aerosol mass spectrometry was used to continuously observe atmospheric fine particulate matter during one-month periods in summer and winter, respectively. The results showed that, apart from O3, the concentrations of other pollutants (CO, NO2, SO2, PM2.5 and PM10) were significantly higher in winter than in summer. All single particle aerosols were divided into seven categories: biomass burning (BB), coal combustion (CC), Dust, vehicle emission (VE), K mixed with nitrate (K-NO3), K mixed with sulfate and nitrate (K-SN), and K mixed with sulfate (K-SO4) particles. The highest contributions in both seasons were VE particles (24%). The higher contributions of K-SO4 (16%) and K-NO3 (10%) particles occurred in summer and winter, respectively, as a result of their different formation mechanisms. S-containing (K-SO4 and K-SN), VE, and BB particles caused the evolution of pollution in both seasons, and they can be considered as targets for future pollution reduction. The mixing of primary sources particles (VE, Dust, CC, and BB) with secondary components was stronger in winter than in summer. In summer, as pollution worsens, the mixing of primary sources particles with 62 [NO3]- weakened, but the mixing with 97 [HSO4]- increased. However, in winter, the mixing state of particles did not exhibit an obvious evolution rules. The potential source areas in summer were mainly distributed in the southern region of Sichuan, while in winter, besides the southern region, the contribution of the western region cannot be ignored.

Spatiotemporal variations and source on black carbon over Chongqing, China: Long-term changes and observational experiments

Black carbon (BC), as a critical light-absorbing constituent within aerosols, exerts profound effects on atmospheric radiation balance, climate, air quality and human health, etc. And it is also a long-standing focus in rapidly developing megacities. So, this study primarily focuses on investigating the variation characteristics and underlying causes of BC in Chongqing (31,914,300 population), which is one of the municipalities directly under the central government of China, serving as a pivotal economic hub in southwest China. Utilizing MERRA-2 reanalysis data, we examined the long-term changes of atmospheric BC over Chongqing 20 years (from 2002 to 2021). Moreover, BC mass concentration observations were conducted using an Aethalometer (AE-33) from March 15 to June 14, 2021 in Liangping District, Chongqing. The statistical analysis over the last 20 years reveals an annual mean BC concentration in Chongqing of 3.42 ± 0.20 μg/m3, exhibiting growth from 2002 to 2008, followed by a decline from 2008 to 2021. Monthly concentration displays a "U-shaped" trend, with the lowest values occurring in summer and the highest in winter. Due to topographical and meteorological influences, local emissions primarily contribute to BC pollution, characterized by a spatial distribution pattern of high in the west and low in the east. Ground observation indicates a distinct dual-peaked pattern in the diurnal variation of BC, with peak concentrations aligning with periods of high traffic emissions. The variation in BC is significantly influenced by meteorological conditions (wind, temperature, atmospheric boundary layer) and local pollution sources (predominantly traffic). Furthermore, extreme events analysis suggests that local emissions and regional transport (with higher contributions from Chongqing and the Sichuan Basin) predominantly contributed to BC pollution. This study effectively makes up for the deficiency in analyzing the distribution and sources of BC pollution in Chongqing, providing valuable scientific insights for the atmospheric environment of megacities.

Exploring secondary aerosol formation associated with elemental carbon in the lower free troposphere

The variability of element carbon (EC) mixed with secondary species significantly complicates the assessment of its environmental impact, reflecting the complexity and diversity of EC-containing particles' composition and morphology during their ascent and regional transport. While the catalytic role of EC in secondary aerosol formation is recognized, the effects of heterogeneous chemistry on secondary species formation within diverse EC particle types are not thoroughly understood, particularly in the troposphere. Alpine sites offer a prime environment to explore EC properties post-transport from the ground to the free troposphere. Consequently, we conducted a comprehensive study on the genesis of secondary aerosols in EC-containing particles at Mt. Hua (altitude: 2069 m) from 1 May to 10 July, using a single particle aerosol mass spectrometer (SPAMS). Our analysis identified six major EC particle types, with EC-K, EC-SN, and EC-NaK particles accounting for 27.6 %, 27.0 %, and 19.6 % of the EC particle population, respectively. The concentration-weighted trajectory (CWT) indicated that the lower free troposphere over Mt. Hua is significantly affected by anthropogenic emissions at ground-level, predominantly from northwestern and eastern China. Atmospheric interactions are crucial in generating high sulfate levels in EC-SN and EC-OC particles (> 70 %) and notable nitrate levels in EC-K, EC-BB, and EC-Fe particles (> 80 %). The observed high chloride content in EC-OC particles (56 ± 32 %) might enhance chlorine's reactivity with organic compounds via heterogeneous reactions within the troposphere. Distinct diurnal cycles for sulfate and nitrate are mainly driven by varying transport dynamics and formation processes, showing minimal dependency on EC particle types. Enhanced nocturnal oxalate conversion in EC-Fe particles is likely due to the aqueous oxidation of precursors, with Fe-catalyzed Fenton reactions enhancing OH radical production. This investigation provides critical insights into EC's role in secondary aerosol development during its transport in the lower free troposphere.

Mutagenicity of PM2.5 and Ethnic Susceptibility in Chengdu-Chongqing Economic Circle, China

PM_2.5 seriously endangers human health, and its mutagenicity is considered an important pathogenic mechanism. However, the mutagenicity of PM_2.5 is mainly determined by traditional bioassays, which are limited in the large-scale identification of mutation sites. Single nucleoside polymorphisms (SNPs) can be used for the large-scale analysis of DNA mutation sites but have not yet been used on the mutagenicity of PM_2.5. The Chengdu-Chongqing Economic Circle is one of China's four major economic circles and five major urban agglomerations, and the relationship between the mutagenicity of PM_2.5 and ethnic susceptibility in this circle remains unclear. In this study, the representative samples are PM_2.5 from Chengdu in summer (CDSUM), Chengdu in winter (CDWIN), Chongqing in summer (CQSUM) and Chongqing in winter (CQWIN) respectively. PM_2.5 from CDWIN, CDSUM and CQSUM induce the highest levels of mutation in the regions of exon/5'Utr, upstream/splice site and downstream/3'Utr respectively. PM_2.5 from CQWIN, CDWIN and CDSUM induce the highest ratio of missense, nonsense and synonymous mutation respectively. PM_2.5 from CQWIN and CDWIN induce the highest transition and transversion mutations respectively. The ability of PM_2.5 from the four groups to induce disruptive mutation effects is similar. For ethnic susceptibility, PM_2.5 in this economic circle is more likely to induce DNA mutation in Chinese Dai from Xishuangbanna among Chinese ethnic groups. PM_2.5 from CDSUM, CDWIN, CQSUM and CQWIN may particularly tend to induce Southern Han Chinese, Dai in Xishuangbanna, Dai in Xishuangbanna and Southern Han Chinese respectively. These findings may assist in the development of a new method for analyzing the mutagenicity of PM_2.5. Moreover, this study not only promotes attention to ethnic susceptibility to PM_2.5, but also introduces public protection policies for the susceptible population.

Enhanced commercial cooking inventories from the city scale through normalized emission factor dataset and big data

Cooking emission inventories always have poor spatial resolutions when applying with traditional methods, making their impacts on ambient air and human health remain obscure. In this study, we created a systematic dataset of cooking emission factors (CEFs) and applied it with a new data source, cooking-related point of interest (POI) data, to build up highly spatial resolved cooking emission inventories from the city scale. Averaged CEFs of six particulate and gaseous species (PM, OC, EC, NMHC, OVOCs, VOCs) were 5.92 ± 6.28, 4.10 ± 5.50, 0.05 ± 0.05, 22.54 ± 20.48, 1.56 ± 1.44, and 7.94 ± 6.27 g/h normalized in every cook stove, respectively. A three-field CEF index containing activity and emission factor species was created to identify and further build a connection with cooking-related POI data. A total of 95,034 cooking point sources were extracted from Beijing, as a study city. In downtown areas, four POI types were overlapped in the central part of the city and radiated into eight distinct directions from south to north. Estimated PM/VOC emissions caused by cooking activities in Beijing were 4.81/9.85 t per day. A 3D emission map showed an extremely unbalanced emission density in the Beijing region. Emission hotspots were seen in Central Business District (CBD), Sanlitun, and Wangjing in Chaoyang District and Willow and Zhongguancun in Haidian District. PM/VOC emissions could be as high as 16.6/42.0 kg/d in the searching radius of 2 km. For PM, the total emissions were 417.4, 389.0, 466.9, and 443.0 t between Q1 and Q4 2019 in Beijing, respectively. The proposed methodology is transferrable to other Chinese cities for deriving enhanced commercial cooking inventories and potentially highlighting the further importance of cooking emissions on air quality and human health.

Impact of reduced anthropogenic emissions on chemical characteristics of urban aerosol by individual particle analysis

A single particle aerosol mass spectrometer was deployed in a heavily polluted area of China during a coronavirus lockdown to explore the impact of reduced anthropogenic emissions on the chemical composition, size distributions, mixing state, and secondary formation of urban aerosols. Ten particle groups were identified using an adaptive resonance network algorithm. Increased atmospheric oxidation during the lockdown period (LP) resulted in a 42.2%-54% increase in the major NaK-SN particle fraction relative to the normal period (NP). In contrast, EC-aged particles decreased from 31.5% (NP) to 23.7% (LP), possibly due to lower emissions from motor vehicles and coal combustion. The peak particle size diameter increased from 440 nm during the NP to 500 nm during LP due to secondary particle formation. High proportions of mixed 62NO3- indicate extensive particle aging. Correlations between secondary organic (43C2H3O+, oxalate) and secondary inorganic species (62NO3-, 97HSO4- and 18NH4+) versus oxidants (Ox = O3 + NO2) and relative humidity (RH) indicate that increased atmospheric oxidation promoted the generation of secondary species, while the effects of RH were more complex. Differences between the NP and LP show that reductions in primary emissions had a remarkable impact on the aerosol particles. This study provides new insights into the effects of pollution emissions on atmospheric reactions and the specific aerosol types in urban regions.

Source Apportionment of Ambient Aerosols during a Winter Pollution Episode in Yinchuan by Using Single-Particle Mass Spectrometry

For a winter pollution episode in Yinchuan, a city in Northwestern China, ambient aerosols were characterized using a real-time single-particle aerosol mass spectrometer (SPAMS). More than 160,000 individual particles analyzed with the SPAMS were classified into eight major categories on the basis of their mass spectral patterns: traffic emissions, biomass burning, dust, coal burning, industrial emissions, secondary inorganic, cooking, and others, all of which contribute to fine particles. The results revealed that coal burning (29.6%) and traffic emissions (23.4%) were the main sources during the monitoring period. Industrial emissions and secondary inorganic aerosols accounted for 16.6% and 14.0%, respectively. The SPAMS data indicated that the number concentration of the eight types of particles was markedly different in the different pollution cases, and higher number concentrations were discovered more often during pollution episodes. The three pollution cases were mainly caused by the accumulation of fine particles, mainly from traffic emissions, industrial emissions, and increased secondary inorganic conversion.

Characterization of the spatial and temporal distribution of lead around a battery industrial park by LA-SPAMS

A convenient technique for direct solids analysis, laser ablation single particle aerosol mass spectrometry (LA-SPAMS), was used to investigate lead and other components in soil and bark samples from around a battery industrial park. In total, over 50,000 particles ranging in size from 0.2 to 2 μm were sampled and approximately 15-35% of the particles were analyzed for chemical composition. The mean mass spectrum results showed that the intensity of lead varied widely among sampling points, reaching the highest intensity in the topsoil and bark at sampling point 4, located closest to the core factory. Based on the neural network algorithm of adaptive resonance theory (ART-2a), the topsoil and bark samples were classified into five categories: crustal composition (Ca⁺, silicates, aluminates, etc.), elemental carbon (C₂^-, C₃^-, C₄^-, etc.), organic carbon (CN^-, levoglucosan, etc.), secondary inorganic sources (phosphates, nitrates, sulfates), and heavy metals (Pb⁺, Zn⁺, Cu⁺), with the proportion of Pb varying from 0.020 to 0.25% and 0.030-9.41% in topsoil and bark samples, respectively, while the proportion of Cu and Zn in topsoil and bark samples did not differ as greatly as Pb. In addition, the particle number concentrations of lead particles in topsoil and bark ranged from 0.14 to 3.48% and 0.36-37.93%, respectively. The concentrations of Pb in topsoil and bark samples measured by ICP-OES varied from 71 to 791 ppm and 172-2595 ppm, respectively. Overall, both the lead content in topsoil samples measured by LA-SPAMS and ICP-OES reached maximum values at sampling points 4 and 5, respectively, indicating moderate pollution with Pb at these two sites. This convenient LA-SPAMS method not only accurately detects the composition of solid samples, the mixing state of particulate matter, and the analytical component sources, but also omits tedious pretreatment steps, reduces the use of organic solvents, and shortens the detection time of solid samples, thereby providing an attractive method for soil environmental quality monitoring.

Particle composition, sources and evolution during the COVID-19 lockdown period in Chengdu, southwest China: Insights from single particle aerosol mass spectrometer data

In order to investigate the effects of the Coronavirus Disease 2019 (COVID-19) lockdown on air quality in cities in southwest China, a single particle aerosol mass spectrometer (SPAMS) and other online equipments were used to measure the air pollution in Chengdu, one of the megacities in this area, before and during the lockdown period. It was found that the concentrations of fine particulate matter (PM2.5), nitric oxide (NO), nitrogen dioxide (NO2), sulfur dioxide (SO2) and carbon monoxide (CO) decreased by 38.6%, 77.5%, 47.0%, 35.1% and 14.1%, respectively, while the concentration of ozone (O3) increased by 57.5% from the time before to the time during lockdown. All particles collected during the study period could be divided into eight categories: biomass burning (BB), coal combustion (CC), vehicle emissions (VE), cooking emissions (CE), Dust, K-nitrate (K-NO3), K-sulfate (K-SO4) and K-sulfate-nitrate (K-SN) particles, and their contributions changed significantly after the beginning of lockdown. Compared to before lockdown, the contribution of VE particles experienced the largest reduction (by 14.9%), whereas the contributions of BB and CE particles increased by 7.0% and 7.3%, respectively, during the lockdown period. Regional transmission was critical for pollution formation before lockdown, whereas the pollution that occurred during the lockdown period was caused mainly by locally emitted particles (such as VE, CE and BB particles). Weighted potential source contribution function (WPSCF) analysis further verified and emphasized the difference in the contribution of regional transmission for pollution formation before and during lockdown. In addition, the potential source area and intensity of the particles emitted from different sources or formation mechanisms were quite different.

Inhalable cigarette-burning particles: Size-resolved chemical composition and mixing state

This study analyzed the size-resolved chemical compositions of cigarette-burning particles (CBPs). CBPs in the size range of 0.2-2.0 μm were characterized using a single particle mass spectrometer (SPAMS). CBPs were found to contain polycyclic aromatic hydrocarbons (PAHs), organonitrate, vinylpyridine, indene, guaiacol, methylindane, and metals such as Fe, Cr, Mn, and Cu. Fresh CBPs showed a single modal size distribution which peaked at 0.40 μm. CBPs in the size range of 0.5-0.1 μm contained more biomass burning markers (K⁺, K₂Cl⁺, and levoglucosan), sulfate, naphthalene, and methylindane than CBPs in the size range of 0.2-0.5 μm. Nicotine is favorable to uptake on large particles (>0.5 μm). Among all particles, 57% contained PAHs. Heavy metals Fe, Mn, Cr, and Cu had mixing ratios of 0.06, 0.57, 0.26, and 0.34 respectively; nicotine and guaiacol had mixing ratios of 0.26 and 0.27; and vinylpyridine, indene, and methylindane had mixing ratios of 0.54, 0.55, and 0.65 respectively. Four particle types were resolved: cigarette-burning biomass burning (CB-BB, 50.3%), CB-BB-Metals (49.3%), CB-Nicotine (0.3%), and CB-Aged (0.1%). These results improve the scientific understanding of CBPs and provide useful references for smoking exposure studies that consider the size-resolved chemical compositions and mixing states of particle-phase components. The result can also benefit the study of exposure to secondhand smoking.

Deposition of ambient particles in the human respiratory system based on single particle analysis: A case study in the Pearl River Delta, China

It is important to evaluate how ambient particles are deposited in the human respiratory system in view of the adverse effects they pose to human health. Traditional methods of investigating human exposure to ambient particles suffer from drawbacks related either to the lack of chemical information from particle number-based measurements or to the poor time resolution of mass-based measurements. To address these issues, in this study, human exposure to ambient particulate matter was investigated using single particle analysis, which provided chemical information with a high time resolution. Based on single particle measurements conducted in the Pearl River Delta, China, nine particle types were identified, and EC (elemental carbon) particles were determined to be the most dominant type of particle. In general, the submicron size mode was dominant in terms of the number concentration for all of the particle types, except for Na-rich and dust particles. On average, around 34% of particles were deposited in the human respiratory system with 13.9%, 7.9%, and 12.6% being distributed in the head, tracheobronchial, and pulmonary regions, respectively. The amount of Na-rich particles deposited was the highest, followed by EC. The overall deposition efficiencies of the Na-rich and dust particles were higher than those of the other particle types due to their higher efficiencies in the head region, which could be caused by the greater sedimentation and impaction rates of larger particles. In the head region, the Na-rich particles made the largest contribution (30.5%) due to their high deposition efficiency, whereas in the tracheobronchial and pulmonary regions, EC made the largest contribution due to its high concentration. In summary, the findings of this initial trial demonstrate the applicability of single particle analysis to the assessment of human exposure to ambient particles and its potential to support traditional methods of analysis.

Mass spectrometry for multi-dimensional characterization of natural and synthetic materials at the nanoscale

Characterization of materials at the nanoscale plays a crucial role in in-depth understanding the nature and processes of the substances. Mass spectrometry (MS) has characterization capabilities for nanomaterials (NMs) and nanostructures by offering reliable multi-dimensional information consisting of accurate mass, isotopic, and molecular structural information. In the last decade, MS has emerged as a powerful nano-characterization technique. This review comprehensively summarizes the capabilities of MS in various aspects of nano-characterization that greatly enrich the toolbox of nano research. Compared with other characterization techniques, MS has unique capabilities for real-time monitoring and tracking reaction intermediates and by-products. Moreover, MS has shown application potential in some novel aspects, such as MS imaging of the biodistribution and fate of NMs in animals and humans, stable isotopic tracing of NMs, and risk assessment of NMs, which deserve update and integration into the current knowledge framework of nano-characterization.

Biotoxic effects and gene expression regulation of urban PM2.5 in southwestern China

Atmospheric fine particulate matter (PM_2.5) causes severe haze in China and is regarded as a threat to human health. The health effects of PM_2.5 vary location by location due to the variation in size distribution, chemical composition, and sources. In this study, the cytotoxicity effect, oxidative stress, and gene expression regulation of PM_2.5 in Chengdu and Chongqing, two typical urban areas in southern China, were evaluated. Urban PM_2.5 in summer and winter significantly inhibited cell viability and increased reactive oxygen species (ROS) levels in A549 cells. Notably, PM_2.5 in winter exhibited higher cytotoxicity and ROS level than summer. Moreover, in this study, PM_2.5 commonly induced cancer-related gene expression such as cell adhesion molecule 1 (PECAM1), interleukin 24 (IL24), and cytochrome P450 (CYP1A1); meanwhile, PM_2.5 commonly acted on cancer-related biological functions such as cell-substrate junction, cell-cell junction, and focal adhesion. In particular, PM_2.5 in Chengdu in summer had the highest carcinogenic potential among PM_2.5 at the two sites in summer and winter. Importantly, cancer-related genes were uniquely targeted by PM_2.5, such as epithelial splicing regulatory protein 1 (ESRP1) and membrane-associated ring-CH-type finger 1 (1-Mar) by Chengdu summer PM_2.5; collagen type IX alpha 3 chain (COL9A3) by Chengdu winter PM_2.5; SH2 domain-containing 1B (SH2D1B) by Chongqing summer PM_2.5; and interleukin 1 receptor-like 1 (IL1RL1) and zinc finger protein 42 (ZNF423) by Chongqing winter PM_2.5. Meanwhile, important cancer-related biological functions were specially induced by PM_2.5, such as cell cycle checkpoint by Chengdu summer PM_2.5; macromolecule methylation by Chengdu winter PM_2.5; endoplasmic reticulum-Golgi intermediate compartment membrane by Chongqing summer PM_2.5; and cellular lipid catabolic process by Chongqing winter PM_2.5. Conclusively, in the typical urban areas of southern China, both summer and winter PM_2.5 illustrated significant gene regulation effects. This study contributes to evaluating the adverse health effects of PM_2.5 in southern China and providing public health suggestions for policymakers.

Tracer-based characterization of source variations of PM2.5 and organic carbon in Shanghai influenced by the COVID-19 lockdown

Air quality in megacities is significantly impacted by emissions from vehicles and other urban-scale human activities. Amid the outbreak of Coronavirus (COVID-19) in January 2020, strict policies were in place to restrict people's movement, bringing about steep reductions in pollution activities and notably lower ambient concentrations of primary pollutants. In this study, we report hourly measurements of fine particulate matter (i.e., PM_2.5) and its comprehensive chemical speciation, including elemental and molecular source tracers, at an urban site in Shanghai spanning a period before the lockdown restriction (BR) (1 to 23 Jan. 2020) and during the restriction (DR) (24 Jan. to 9 Feb. 2020). The overall PM_2.5 was reduced by 27% from 56.2 ± 40.9 (BR) to 41.1 ± 25.3 μg m^-3 (DR) and the organic carbon (OC) in PM_2.5 was similar, averaged at 5.45 ± 2.37 (BR) and 5.42 ± 1.75 μgC m^-3 (DR). Reduction in nitrate was prominent, from 18.1 (BR) to 9.2 μg m^-3 (DR), accounting for most of the PM_2.5 decrease. Source analysis of PM_2.5 using positive matrix factorization modeling of comprehensive chemical composition, resolved nine primary source factors and five secondary source factors. The quantitative source analysis confirms reduced contributions from primary sources affected by COVID-19, with vehicular emissions showing the largest drop, from 4.6 (BR) to 0.61 μg m^-3 (DR) and the percentage change (-87%) in par with vehicle traffic volume and fuel sale statistics (-60% to -90%). In the same time period, secondary sources are revealed to vary in response to precursor reductions from the lockdown, with two sources showing consistent enhancement while the other three showing reductions, highlighting the complexity in secondary organic aerosol formation and the nonlinear response to broad primary precursor pollutants. The combined contribution from the two secondary sources to PM_2.5 increased from 7.3 ± 6.6 (BR) to 14.8 ± 9.3 μg m^-3 (DR), partially offsetting the reductions from primary sources and nitrate while their increased contribution to OC, from 1.6 ± 1.4 (BR) to 3.2 ± 2.0 μgC m^-3 (DR), almost offset the decrease coming from the primary sources. Results from this work underscore challenges in predicting the benefits to PM_2.5 improvement from emission reductions of common urban primary sources.

Fossil fuel CO2 traced by radiocarbon in fifteen Chinese cities

China is an important fossil fuel CO₂ (CO_2ff) emitter and the international community is thus concerned with quantifying reductions in Chinese carbon emissions in the recent past. Compared to traditional statistical method, radiocarbon (¹⁴C) offers a different approach to quantify atmospheric CO₂ derived from fossil fuel emissions. Here, we carry out a multi-year (2011-2016) CO_2ff tracing by ¹⁴C in Xi'an, and a three-year (2014-2016) CO_2ff tracing in 15 Chinese cities. The Xi'an results show that average CO_2ff concentrations fell 35.9 ± 6.6% from 2014- 2016, compared to 2011-2013, and the timing of this decrease coincides with the implementation of nationwide carbon reduction measures in China, known as the Action Plan on Prevention and Control of Air Pollution. A WRF-Chem forward modeling simulation reveals that the CO_2ff in Xi'an is mainly derived from local sources, and a source apportionment combined stable-carbon isotope showed that the CO_2ff in this city is dominated by coal combustion (72.6 ± 10.4%). Strong CO_2ff differences are found between January and July in most Chinese cities. High CO_2ff concentrations often correspond to severe haze episodes and there are generally positive correlations between CO_2ff and fine particulate (PM_2.5) concentrations. Our study provides scientific data to understand the effects of CO_2ff reduction strategies in China that can be applied to other countries as well.

Brown carbon aerosol in two megacities in the Sichuan Basin of southwestern China: Light absorption properties and implications

The light absorption of brown carbon (BrC) makes a significant contribution to aerosol light absorption (Abs) and affects the radiative forcing. In this study, we analyzed and evaluated the light absorption and radiative forcing of BrC samples collected from December 2016 to January 2017 in Chongqing and Chengdu in the Sichuan Basin of Southwest China. Based on a two-component model, we estimated that BrC light absorption at 405 nm was 19.9 ± 17.1 Mm^-1 and 19.2 ± 12.3 Mm^-1 in Chongqing and Chengdu, contributing 19.0 ± 5.0% and 17.8 ± 3.7% to Abs respectively. Higher Abs_405,BrC, MAE_405,BrC, and AAE_405-980 values were observed during the pollution period over the clean period in both cities. The major sources of BrC were biomass burning (BB) and secondary organic aerosol in Chongqing, and coal combustion (CC) and secondary organic aerosol in Chengdu. During the pollution period, aged BrC formed from anthropogenic precursors via its aqueous reactions with NH₄⁺ and NOx had impacts on BrC absorption in both cities. BB led to higher Abs_405,BrC, MAE_405,BrC, and AAE_405-980 values in Chongqing than Chengdu during the pollution period. The fractional contribution of radiation absorbed by BrC relative to BC in the wavelengths of 405-445 nm was 60.2 ± 17.0% and 64.2 ± 11.6% in Chongqing and Chengdu, significantly higher than that in the range of 405-980 nm (26.2 ± 6.7% and 27.7 ± 4.6% respectively) (p < 0.001). This study is useful for understanding the characterization, sources, and impacts of BrC in the Sichuan Basin.

Identifying the wintertime sources of volatile organic compounds (VOCs) from MAX-DOAS measured formaldehyde and glyoxal in Chongqing, southwest China

Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations were performed from 27 December 2018 to 16 January 2019 in Changshou, one of subdistricts of Chongqing, China. Primary atmospheric pollutant in Changshou during wintertime was PM_2.5, whose contribution averaged about 70.15% ± 9.5% of PM₁₀. The ratio of PM_2.5/PM₁₀ decreased when PM_2.5 pollution became worse, and it should attribute to biomass burning and the contribution of hygroscopic growth and enhanced heterogeneous chemistry under high relative humidity condition. Moreover, nitrogen dioxide (NO₂), formaldehyde (HCHO) and glyoxal (CHOCHO) vertical profiles during the campaign period were retrieved separately. TROPOMI HCHO vertical column densities (VCDs) and MAX-DOAS HCHO VCDs were correlated well (R = 0.93). In order to identify the sources of volatile organic compound (VOC) in Changshou, the ratio of CHOCHO to HCHO (R_GF) in five different layers were estimated. The estimated daily averaged R_GF were 0.0205 ± 0.0077, 0.0727 ± 0.0286, 0.0864 ± 0.0296, 0.0770 ± 0.0275 and 0.0746 ± 0.0263 in 0-100 m, 100-200 m, 300-400 m, 500-600 m and 700-800 m layers, respectively. The estimated R_GF will increase when biomass burnings were dominated. Using NO₂ as a tracer of anthropogenic emissions, we found the R_GF values gradually decrease with the increase of NO₂ levels. R_GF values in 0-100 m layer and all the other upper layers are 0.015-0.025 and 0.06-0.14, and that means the dominant sources of VOCs in 0-100 m layer and all the other upper layers are biogenic emission and anthropogenic emission (especially biomass burning), respectively. In addition, we found that R_GF has site dependence which is in compliance with several previous studies.

Characteristics of single atmospheric particles in a heavily polluted urban area of China: size distributions and mixing states

To investigate the chemical composition, size distribution, and mixing state of aerosol particles on heavy pollution days, single-particle aerosol mass spectrometry was conducted during 9-26 October 2015 in Xi'an, China. The measured particles were classified into six major categories: biomass burning (BB) particles, K-secondary particles, elemental carbon (EC)-related particles, metal-containing particles, dust, and organic carbon (OC) particles. BB and EC-related particles were the dominant types during the study period and mainly originated from biomass burning, vehicle emissions, and coal combustion. According to the ambient air quality index, two typical episodes were defined: clean days (CDs) and polluted days (PDs). Accumulation of BB particles and EC-related particles was the main reason for the pollution in Xi'an. Most types of particle size were larger on PDs than CDs. Each particle type was mixed with secondary species to different degrees on CDs and PDs, indicating that atmospheric aging occurred. The mixing state results demonstrated that the primary tracers were oxidized or vanished and that the amount of secondary species was increased on PDs. This study provides valuable information and a dataset to help control air pollution in the urban areas of Xi'an. Graphical abstract.

Characterization of water soluble inorganic ions and their evolution processes during PM2.5 pollution episodes in a small city in southwest China

PM_2.5 samples were collected in four segregate one-month periods, each representing one season, for analyzing their contents of water soluble inorganic ions (WSIIs) in a small city inside Sichuan Basin. Daily PM_2.5 concentrations ranged from 23.2 to 203.1 μg m^-3 with an annual mean of 66.9 ± 33.6 μg m^-3. Annual mean concentrations of WSIIs was 28.8 ± 20.3 μg m^-3, accounting for 43.1% of PM_2.5. Seasonal mean concentrations of WSIIs ranged from 17.5 ± 9.3 μg m^-3 in summer to 46.5 ± 27.6 μg m^-3 in winter. Annual mean mass ratio of NO₃^-/SO₄^2- was 0.49, demonstrating predominant stationary sources for secondary inorganic aerosols (SNA, including SO₄^2-, NH₄⁺ and NO₃^-); whereas annual mean molar ratio of [NH₄⁺]/[NO₃^-] was 3.5, suggesting dominant agriculture emissions contributing to the total nitrogen. During a severe and long-lasting (13 days) winter pollution period when mean PM_2.5 concentration reached to 132.5 μg m^-3, PM_2.5 concentration was enhanced by a factor of 2.6 while that of SNA by a factor of 2.9 compared to those before the pollution event, and the fraction of SNA in PM_2.5 only increased slightly (from 46.7% to 50.6%). Thus, local accumulation of pollutants under poor diffusion conditions played a major role causing the extremely high PM_2.5 concentration, besides the contributions from the enhanced SNA formation under specific weather conditions.

Characteristics and sources of trace elements in PM2.5 in two megacities in Sichuan Basin of southwest China

To characterize major trace elements in PM_2.5 and associated sources in two megacities, Chengdu (CD) and Chongqing (CQ), in Sichuan Basin of southwest China, daily PM_2.5 samples were collected at one urban site in each city from October 2014 to July 2015 and were analyzed for their contents of thirteen trace elements including four crustal elements (Al, Ca, Fe, and Ti), eight trace metals (K, Cr, Zn, Cu, Mn, Pb, Ni, and V), and As. Multiple approaches including correlation analysis, enrichment factor, principal component analysis, and conditional probability function (CPF) were applied to identify potential sources of these elements. Most of the measured trace elements in Sichuan Basin were found to have lower concentrations than in the other regions of China. K and Fe were the most abundant elements at CD with an annual mean concentrations of 720 ± 357 and 456 ± 248 ng m^-3, accounting for 34.6% and 21.9% of the total analyzed trace elements, respectively. Ca presented the highest concentration among all of the elements at CQ with annual mean of 824 ± 633 ng m^-3 (29.1% of the total). Crustal elements had the highest concentrations in spring while heavy metals had distinct seasonal variations typically with the highest concentrations in winter and the lowest in summer. Ti and Al were identified to be primarily from soil while most of the analyzed heavy metals (Cr, Mn, Cu, Zn, Pb, Ni) and As were from anthropogenic sources associated with coal combustion, industrial emission from glassmaking production and iron/steel manufacturing, and non-exhaust vehicle emission.

Single particle characterization of summertime particles in Xi'an (China)

Urban particles in Xi'an during summertime were investigated using a single particle aerosol mass spectrometer (SPAMS). Twelve major particle types were resolved, including EC-Sul-Nit (-Sul stands for sulfate, -Nit for nitrate, and 25% in number fraction), EC(6%), EC-Nit (12%) and, EC-Sul (8%), mixed Elemental and Organic Carbon-Sul-Nit (9%), ECOC-Sul (8%), K-Nit (12%), OC (8%), NaK-Nit (5%), Fe-Nit (5%), Ca-Nit (1%), and Other (1%). Among these particle types, chemical composition, mixing state, and wind-dependent analyses were conducted to investigate their originations and sources. During summertime, traffic-related particles were up to 83% in the SPAMS dataset. Two major originations of urban particles were identified, including the local aging and short-distance transport mainly from the southeast. Size-resolved relative acidity ((sulfate + nitrate) / ammonium) analysis suggested that urban particles were more acidic with an aerodynamic diameter < 0.8 μm. In diurnal cycle, the strongest relative aerosol acidity occurred between 7:00 and 9:00 in the morning when relative humidity was between 60 and 70%, and the weakest acidity occurred from 13:00-15:00. Among all major particle types, OC and K-Nit had stronger relative aerosol acidity than other types. Mixing state analysis indicated that the organic semi-volatile vapor is favorable to condense on the OC-related particles (OC, ECOC-Sul, and ECOC-Sul-Nit) as evidence that primary organic aerosol (POA) would enhance the secondary organic aerosol (SOA) formation via gas-to-particle phase partitioning when SOA and POA are miscible. Oxalate also tends to be observed in the droplet of OC-related particles. In addition, the enrichment of oxalate was observed in Fe-Nit particles. This study would be useful to understand the characterization, mixing state, source, origination, and processing of urban particles during summertime in Xi'an as well as the urban areas in the Guanzhong Basin.