Nitroaromatic compounds in six major Chinese cities: Influence of different formation mechanisms on light absorption properties.

Nitroaromatic compounds (NACs) are important nitrogen organics in aerosol with strong light-absorbing and chemically reactive properties. In this study, NACs in six Chinese megacities, including Harbin (HB), Beijing (BJ), Xi'an (XA), Wuhan (WH), Chengdu (CD), and Guangzhou (GZ), were investigated for understanding their sources, gas-particle partitioning, and impact on BrC absorption properties. The concentrations of ΣNACs in PM2.5 in the six cities ranged from 9.15 to 158.8 ng/m3 in winter and from 2.02 to 9.39 ng/m3 in summer. Nitro catechols (NCs), nitro phenols (NPs), and nitro salicylic acids (NSAs) are the main components in ΣNACs, with NCs being dominant in particulate phase and NPs being dominant in the gas phase. Correlation analysis between different pollutant species revealed that coal and biomass combustions were the major sources of NACs in the northern cities during wintertime, while secondary formation dominated NACs in the southern cities during summertime. The contribution of ΣNACs to brown carbon (BrC) light absorption ranged from 0.85 to 7.98 % during the wintertime and 2.07-6.44 % during the summertime. The mass absorption efficiency at 365 nm (MAE365) were highest for 4-nitrocatechol (4NC, 17.4-89.0 m2/g), 4-methyl-5-nitrocatechol (4M5NC, 15.0-76.9 m2/g), and 4-nitroguaiacol (4NG, 11.7-59.8 m2/g). The formation of NCs and NG through oxidation and nitration of catechol and guaiacol led to a significant increase in aerosol light absorption. In contrast, NPs and NSAs formed by the photonitration and photooxidation in liquid phase showed high polarity but low light absorption ability, and the proportions of (NPs + NSAs) in the light absorption of ΣNACs were lower than 15.3 % in the six megacities.

Optical properties and radiative forcing of carbonaceous aerosols in a valley city under persistent high temperature.

Carbonaceous aerosols were collected in the valley city of Baoji city in Northern China in August 2022. The light absorption characteristics and influencing factors of black carbon (BC) and brown carbon (BrC) were analyzed, and their radiative forcing was estimated. The results showed that the light absorption of secondary brown carbon [AbsBrC,sec (370)] was 7.5 ± 2.4 Mm-1, which was 2.5 times that of primary brown carbon [AbsBrC,pri (370), 3.0 ± 1.2 Mm-1]. During the study period, the absorption Ångström exponent (AAE) of aerosol was 1.6, indicating that there was obvious secondary aerosol formation or carbonaceous aerosol aging in the valley city of Baoji. Except for secondary BrC (BrCsec), the light absorption coefficient (Abs) and mass absorption efficiency (MAE) of BC and primary BrC (BrCpri) during the persistent high temperature period (PHT) were higher than those during the normal temperature period (NT) and the precipitation period (PP), which indicated that the light absorption capacity of black carbon and primary brown carbon increased, while the light absorption capacity of secondary brown carbon decreased under persistent high temperature period. Secondary aerosols sulfide (SO42-), nitrate (NO3-) and secondary organic carbon (SOC) are important factors for promoting the light absorption enhancemen of BC and BrCpri and photobleaching of BrCsec during persistent high temperature period. The Principal Component Analysis-Multiple Linear Regression (PCA-MLR) model showed that traffic emissions was the most important source of pollution in Baoji City. Based on this, the secondary source accelerates the aging of BC and BrC, causing changes in light absorption. During PHT, the radiative forcing of BC and BrCpri were enhanced, while the radiative forcing of BrCsec was weakened, but the positive radiative forcing generated by them may aggravate the high-temperature disaster.

Personal exposure monitoring of fine and coarse particulate matter using exposure assessment models for elderly residents in Hong Kong.

This study investigated the determinants of personal exposures (PE) to coarse (PM2.5-10) and fine particulate matter (PM2.5) for elderly communities in Hong Kong. The mean PE PM2.5 and PM2.5-10 were 23.6 ± 10.8 and 13.5 ± 22.1 µg/m3, respectively during the sampling period. Approximately 76% of study subjects presented statistically significant differences between PE and ambient origin for PM2.5 compared to approximately 56% for PM2.5-10, possibly due to the coarse-size particles being more influenced by similar sources (road dust and construction dust emissions) compared to the PM2.5 particles. Individual PE to ambient (P/A) ratios for PM2.5 all exceeded unity (≥1), suggesting the dominant influences of non-ambient particles contributed towards total PE values. There were about 80% individual P/A ratios (≤1) for PM2.5-10, implying possible effective infiltration prevention of larger size particulate matter particles leading to dominant influences from the outdoor sources. The higher concentration of NO3- and SO42- in PM2.5-10 compared to PM2.5 suggests possible heterogeneous reactions of alkaline minerals leading to the formation of NO3- and SO42- in PM2.5-10 particles. The PE and ambient OC/EC ratios in PM2.5 (8.8 ± 3.3 and 10.4 ± 22.4, respectively) and in PM2.5-10 (6.0 ± 1.9 and 3.0 ± 1.1, respectively) suggest possible secondary formed OC from surrounding rural areas. Heterogeneous distributions (COD >0.2) between the PE and ambient concentrations were found for both the PM2.5 and PM2.5-10 samples. The calibration coefficient as the association between personal and surrogate exposure measure of PE to PM2.5 (0.84) was higher than PM2.5-10 (0.52). The findings further confirm that local sources were the dominant contributor to the coarse particles and these coefficients can potentially be used to estimate different PE to PM2.5 and PM2.5-10 conditions. A comprehensive understanding of the PE to determinants in coarse particles is essential to further reduce potential exposure misclassification.

Toxicity source apportionment of fugitive dust PM2.5-bound polycyclic aromatic hydrocarbons using multilayer perceptron neural network analysis in Guanzhong Plain urban agglomeration, China.

Polycyclic aromatic hydrocarbons (PAHs) in urban fugitive dust, known for their toxicity and ability to generate reactive oxygen species (ROS), are a major public health concern. This study assessed the spatial distribution and health risks of 15 PAHs in construction dust (CD) and road dust (RD) samples collected from June to November 2021 over the cities of Tongchuan (TC), Baoji (BJ), Xianyang (XY), and Xi'an (XA) in the Guanzhong Plain, China. The average concentration of ΣPAHs in RD was 39.5 ± 20.0 µg g-1, approximately twice as much as in CD. Four-ring PAHs from fossil fuels combustion accounted for the highest proportion of ΣPAHs in fugitive dust over all four cities. Health-related indicators including benzo(a)pyrene toxic equivalency factors (BAPTEQ), oxidative potential (OP), and incremental lifetime cancer risk (ILCR) all presented higher risk in RD than those in CD. The multilayer perceptron neural network algorithm quantified that vehicular and industrial emissions contributed 86 % and 61 % to RD and CD BAPTEQ, respectively. For OP, the sources of biomass and coal combustion were the key generator which accounted for 31-54 %. These findings provide scientific evidence for the direct efforts toward decreasing the health risks of fugitive dust in Guanzhong Plain urban agglomeration, China.

Characteristics and sources of oxygenated VOCs in Hong Kong: Implications for ozone formation.

To investigate the characteristics of oxygenated volatile organic compounds (OVOCs) and their potential contribution to ozone (O3) generation, we conducted 3-h high-resolution observations during the summertime of 2022 and the wintertime of 2021. This study focused on a total of 28 OVOCs in five different chemical classes, which were encompassed at two representative sites in Hong Kong, including a roadside and an urban area. During the summertime, the total concentrations of quantified OVOCs (∑OVOCs) were 45 ± 12 and 63 ± 20 µg m-3 at the roadside and urban sites, respectively, whereas the ∑OVOCs decreased by 31 ± 11 % and 38 ± 13 %, respectively, during the wintertime. Among the classes of OVOCs, carbonyls and alcohols were the two predominant at both sites, with relatively higher concentration levels of acetone, methanol, butanaldehyde, and acrolein. The sources of OVOCs have significant spatial and temporal characteristics. Spatially, OVOCs were predominately attributed to primary emission and background at the roadside site, whereas they were a combination of primary emission, secondary formation, and background at the urban site. Temporally, background sources dominated the summertime OVOCs, while the contribution of primary emissions increased for the wintertime OVOCs. The O3 formation potential (OFP) for the OVOCs was calculated. The OFPs were 67 ± 16 and 119 ± 31 µg m-3 at the roadside and urban sites during the summertime, whereas the winter OFPs declined 30 % at the roadside and 38 % at the urban site. The background sources of carbonyls and alcohols at the roadside and of carbonyls and acrylates in the urban area were the major contributors to the summer OFP. Controlling the OVOC sources from local non-combustion sources such as gasoline-fuel evaporation and volatile chemical-containing products could lead to a reduction of OVOCs in the background and subsequently mitigate the OFP. This is beneficial for local O3 reduction in Hong Kong and surrounding regions.

Elaborations of the influencing factors on the formation of secondary inorganic aerosols in a heavily polluted urban area of China.

In this study, online water-soluble inorganic ions were detected to deduce the formation mechanism of secondary inorganic aerosol in Xianyang, China during wintertime. The dominant inorganic ions of sulfate (SO42-), nitrate (NO3-), and ammonium (NH4+) (the sum of those is abbreviated as SNA) accounted for 17%, 21%, and 12% of PM2.5 mass, respectively. While the air quality deteriorated from excellent to poor grades, the precursor gas sulfur dioxide (SO2) of SO42- increased and then decreased with a fluctuation, while nitrogen dioxide (NO2) and ammonia (NH3), precursors of NO3- and NH4+, and SNA show increasing trends. Meteorological factors including boundary layer height (BLH), temperature, and wind speed also show decline trends, except relative humidity (RH). Meanwhile, the secondary conversion ratio shows a remarkable increasing trend, indicating that there was a strong secondary transformation. From the perspective of chemical mechanisms, RH is positively correlated with sulfur oxidation ratios (SOR), nitrogen oxidation ratios (NOR), and ammonia conversion ratios, representing that the increase of humidity could promote the generation of SNA. Notably, SOR and NOR were also positively related to the ammonia. On the one hand, the low wind speed and BLH led to the accumulation of pollutants. On the other hand, the increases of RH and ammonia promoted more formations of SNA and PM2.5. The results advance our identification of the contributors to the haze episodes and assist to establish more efficient emission controls in Xianyang, in addition to other cities with similar emission and geographical characteristics.

Insight into personal exposure characteristics and health effects of PM2.5 and PM0.25-bound PAHs and their derivatives with different heating ways in the Fenwei Plain, China.

Personal exposure (PE) to polycyclic aromatic hydrocarbons (PAHs) and their derivatives in particulate matter with two aerodynamic sizes of 2.5 and 0.25 µm (PM2.5 and PM0.25) from rural housewives was studied in the Fenwei Plain, China. A total of 15 households were divided into five different groups based on the type of solid fuel and heating device used, including biomass briquette-furnace (BBF), biomass-elevated Kang (BEK), outdoor lump coal-boiler (OLC), indoor briquette coal-stove (IBC), and electricity (ELE). The PE concentrations of the PAHs and biomarkers in urine collected from the participants were determined. The results showed that the PE concentrations of total quantified PAHs in the biomass group (i.e., BBF and BEK) were 2.2 and 2.0 times higher than those in the coal groups (i.e., OLC and IBC) in PM2.5 and PM0.25, respectively. The housewives who used biomass as fuel suffered from higher potential health impacts than the coal fuel users. The incremental lifetime cancer risk for the PAHs in PM2.5 in the BBF and BEK groups exceeded the international safety threshold. Furthermore, the PE concentrations of oxygenated PAH (o-PAHs) in PM2.5 and PM0.25 in the biomass groups and the nitrated PAHs (n-PAHs) in PM0.25 in the coal groups showed strong correlations with the biomarkers. The results of this study proved the associations between exposure to the different classes of PAHs and health hazards. The findings could also serve as a guideline in establishing efficient measures for using solid fuels for cooking and household warming in northern China.

Insight into the Primary and Secondary Particle-Bound Methoxyphenols and Nitroaromatic Compound Emissions from Solid Fuel Combustion and the Updated Source Tracers.

Methoxyphenols and nitroaromatic compounds (NACs) have strong atmospheric radiative forcing effects and adverse effects on human health. They are emitted from the incomplete combustion of solid fuels and are secondarily formed through photochemical reactions. Here, an on-site study was conducted to determine the primary emission and secondary formation of particulate phase products from a variety of solid fuels through a potential aerosol mass-oxidation flow reactor. Emission factors for total quantified methoxyphenols and NACs (i.e., EF∑Methoxyphenols and EF∑NACs) varied by 2 orders of magnitude among different fuels, which were greatly influenced by volatile matter, incomplete combustibility, flame intensity, and combustion temperature. Guaiacol and 4-nitro-2-vinylphenol were used as tracers for primary organic aerosol due to the low aged-to-fresh ratios (0.21-0.97), while 4-methyl-guaiacol, 4-ethyl-guaiacol, eugenol, 4-methyl-syringol, isoeugenol, acetovanillone, syringaldehyde, homovanillin acid, vanillin acid, and syringic acid were identified as secondary organic aerosol (SOA) (aged-to-fresh ratios between 1.90 and 4.20). During simulated aging, the -CHO group reacted with the hydroxyl radical (•OH) to form the -COOH group, but there was no correlation between syringol and 4-nitrosyringol, implying that •OH is the main reactant rather than the nitriate radical (•NO3) in the atmospheric aging processes of methoxyphenols. Aging caused substantially different emission profiles due to variable photochemical reaction properties. The fresh EFs for guaiacol emitted from the biomass burning ranged from 3.80 ± 0.44 to 26.2 ± 5.40 mg·kg-1, which were much higher than those in coal combustions (of 0.03 ± 0.01 to 1.42 ± 0.28 mg·kg-1). However, the aged EFs (EFaged) for guaiacol was 1.02 ± 0.06 to 1.61 ± 0.11 mg·kg-1 in most biomass combustions, which were comparable with those of the bituminous chunk (1.20 ± 0.16 mg·kg-1). Therefore, guaiacol, a traditional biomass marker, is not an ideal tracer for aged PM2.5 emitted from biomass burning. Indeed, the syringol/guaiacol and syringol/4-nitrosyringol ratios were found to be more suitable and efficient to be used in source characterization.

Contributions of non-tailpipe emissions to near-road PM2.5 and PM10: A chemical mass balance study.

As the importance of non-tailpipe particles (NTP) over tailpipe emissions from urban traffic has been increasing, there is a need to evaluate NTP contributions to ambient particulate matter (PM) using representative source profiles. The Brake and Tire Wear Study conducted in Los Angeles, California in the winter of 2020 collected 64 PM2.5 and 64 PM10 samples from 32 pairs of downwind-upwind measurements at two near-road locations (I-5 in Anaheim and I-710 in Long Beach). These samples were characterized for inorganic and organic markers and, along with locally-developed brake wear, tire wear, and road dust source profiles, subject to source apportionment using the effective-variance chemical mass balance (EV-CMB) model. Model results highlighted the dominance of resuspended dust in both PM2.5 (23-33%) and PM10 (32-53%). Brake and tire wear contributed more to PM2.5 than tailpipe exhausts (diesel + gasoline) for I-5 (29-30% vs. 19-21%) while they were comparable for I-710 (15-17% vs. 15-19%). For PM10, the brake and tire wear contributions were 2-3 times the exhaust contributions. Different fleet compositions on and near I-5 and I-710 appeared to influence the relative importance of NTP and exhaust sources. The downwind-upwind differences in source contributions were often insignificant, consistent with small and/or nearly equal impacts of adjacent highway traffic emissions on the downwind and upwind sites. The utility of sole markers, such as barium and zinc, to predict brake and tire wear abundances in ambient PM is evaluated.

Environmental and health impacts of household energy conversion on PAHs and their derivatives in PM2.5 in typical areas of northern China.

Heavy use of solid fuels in rural households of northern China emits huge amounts of fine particulate matter (i.e., PM2.5) that pose notable indoor air pollution and severe inhalation health risks. In this study, the environmental and health benefits of clean energy substitution were accessed by monitoring indoor and personal exposure to polycyclic aromatic hydrocarbons (PAHs) and their derivatives, and pulmonary function and biological parameters. After substitutions of traditional lump coal and biomass fuels by clean coal, indoor concentrations of parent PAHs (p-PAHs), alkylated PAHs (a-PAHs), oxygenated PAHs (o-PAHs), and nitro PAHs (n-PAHs) reduced by 71 %, 32 %, 70 %, and 76 %, while personal exposure concentrations decreased by 82 %, 87 %, 93 %, and 86 %, respectively. However, the proportion of low molecular weight PAHs increases, especially for 2-ring a-PAHs and 3-ring n-PAHs. Domestic solid fuel burning induces greater damage to the small airway than the large airway. Pulmonary function parameter reductions in the clean coal group are much less than those in the other two fuel groups. Salivary interleukin-6 (IL-6) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) significantly correlated with PAH species, among which p-PAHs and PAHs derivatives strongly with IL-6 and 8-OHdG, respectively. The correlation between PAHs and biomarkers in urine is insignificant. In addition, the use of clean coal can reduce the cancer risk for the four classes of PAHs by 60 %-97 %, mainly owing to the lower contributions from p-PAHs and o-PAHs. The result of the study provides scientific support for clean energy retrofit and an understanding of health benefits from solid fuel substitutions.

Chemical composition and potential health risks of tire and road wear microplastics from light-duty vehicles in an urban tunnel in China.

Tire and road wear microplastics (TRWMPs) are one of the main non-exhaust pollutants of motor vehicles, which cause serious environmental and health issues. Here, TRWMPs in PM2.5 samples were collected in a tunnel in urban Xi'an, northwest China, during four periods [I: 7:30-10:30, II: 11:00-14:00, III: 16:30-19:30, IV: 20:00-23:00 local standard time (LST)] in summer of 2019. The chemical components of rubbers, benzothiazoles, phthalates, and amines in TRWMPs were quantified, with a total concentration of 6522 ± 1455 ng m-3 (mean ± standard deviation). Phthalates were predominant in TRWMPs, accounting for 64.8% on average, followed by rubbers (33.2%) and benzothiazoles (1.19%). The diurnal variations of TRWMPs showed the highest concentration in Period III (evening rush hour) and the lowest concentration in Period I (morning rush hour), which were not exactly consistent with the variation of the number of light-duty vehicles passed through the tunnel. The result implied that the number of vehicles might not be the most important contributor to TRWMPs concentration, whereas meteorological variables (i.e., precipitation, and relative humidity), vehicle speed, vehicle class, and road cleaning also affected their abundances. The non-carcinogenic risk of TRWMPs in this study was within the international safety threshold, but their carcinogenic risk exceeded the threshold by 2.7-4.6 times, mostly dominated by bis(2-ethylhexyl)phthalate (DEHP). This study provides a new basis for the source apportionment of urban PM2.5 in China. The high concentrations and high potential cancer risks of TRWMPs represent the requirement for more efficient measures to control light-duty vehicle emissions.

Characterization of chemical components of fresh and aged aerosol from vehicle exhaust emissions in Hong Kong.

The chemical properties of fresh and aged aerosol emitted during controlled vehicular exhaust emissions were characterized in the analysis. Pyrene (10417.1 ± 534.9 ng kg-1) is the most abundant of all analyzed compounds in total fresh emission and succinic acid (57359.8 ± 4000.3 ng kg-1) is for the total aged emission. The fresh emission factors (EFfresh) of all compounds in the n-alkanes group demonstrate higher average emissions for the two vehicles with EURO 3 standard compared to the other vehicles. The EFfresh for benzo [a]pyrene is in descending order: G1 (183.1 ± 144.7 ng kg-1) > G3 (103.4 ± 60.1 ng kg-1) > G4 (91.2 ± 80.1 ng kg-1) > G2 (88.6 ± 93.9 ng kg-1). Aged/fresh (A/F) emission ratios (>20) confirmed that these diacid compounds are generated by the photooxidation of primary pollutants that emitted from gasoline combustions. High A/F ratios (>200) in phthalic acid, isophthalic acid and terephthalic acid under idling mode imply relatively more intense photochemical reactions for their productions compared with other chemical groups. Strong positive correlations (r > 0.6) were observed between the degradation of toluene and formations of pinonic acid, succinic acid, adipic acid, terephthalic acid, glutaric acid and citramalic acid after the aging process, suggesting possible photooxidation of toluene that can lead to secondary organic aerosol (SOA) formation in the urban atmosphere. The findings demonstrate that vehicle emission standards for pollution in relation to the change of particulate matter chemical compositions and SOA formations. The results warrant a need for regulated reformulation for such vehicles.

Heterogeneous characteristics and absorption enhancement of refractory black carbon in an urban city of China.

In this study, field measurement was conducted using an integrated online monitoring system to characterize heterogeneous properties and light absorption of refractory black carbon (rBC). rBC particles are mainly from the incomplete combustion of carbonaceous fuels. With the data collected from a single particle soot photometer, thickly coated (BCkc) and thinly coated (BCnc) particles are characterized with their lag times. With different responses to the precipitation, a dramatical decline of 83 % in the number concentration of BCkc is shown after rainfall, while that of BCnc decreases by 39 %. There is a contrast in core size distribution that BCkc is always with larger particle sizes but has smaller core mass median diameters (MMD) than BCnc. The mean rBC-containing particle mass absorption cross-section (MAC) is 6.70 ± 1.52 m2 g-1, while the corresponding rBC core is 4.90 ± 1.02 m2 g-1. Interestingly, there are wide variations in the core MAC values which range by 57 % from 3.79 to 5.95 m2 g-1, which are also closely related to those of the whole rBC-containing particles with a Pearson correlation of 0.58 (p < 0.01). Errors would be made if we eliminate the discrepancies and set the core MAC as a constant when calculating absorption enhancement (Eabs). In this study, the mean Eabs is 1.37 ± 0.11 while the source apportionment shows that there are five contributors of Eabs including secondary aging (37 %), coal combustion (26 %), fugitive dust (15 %), biomass burning (13 %) and traffic-related emissions (9 %). Secondary aging is found to be the highest contributor due to the liquid phase reactions in formations of secondary inorganic aerosol. Our study characterizes property diversities and provides insights into the sources impacting the light absorption of rBC and will be helpful for controlling it in the future.

Insights into the nitroaromatic compounds, formation, and light absorption contributing emissions from various geological maturity coals.

Nitroaromatic compounds (NACs) are essential components of atmospheric organic aerosols. Coal combustion is a key source of atmospheric NACs. In this study, a triple-quadrupole liquid chromatography-mass spectrometry (LC-MS) system was used to identify ten individual NAC emitted in combustions of chunk coal and its briquette at different maturity levels. The Gaussian calculation was applied to quantify the absorption contribution of NACs to brown carbon (BrC). The emission factors (EFs) of total quantified NACs (ΣNACs) are 21.80-4429.55 µg/kg. 4-Nitrocatechol (4NC) is the most abundant NACs, accounting for 25.5-82.3 % of the ΣNACs and has the largest contribution to light absorption (0.34-29.23 %). The EFs for ΣNACs of chunk coal are 1.1-3.0 times those of its briquette, while the coal with volatile matter (VM) = 35.83 % shows the highest NAC emissions. The reaction pathway analysis demonstrates that NACs in briquette are generated through the pyrolysis of coal tar at an early stage of coal combustion, while volatile organic compounds (VOCs) that are emitted in chunk coal contribute greatly to the formations of NACs. The molecular properties analysis reveals that ΣNACs contribute 0.47-35.27 % to BrC light absorption. Anthracite coal (VM = 8.01 %) demonstrates the lowest light absorption coefficient (babs-365). Since bituminous coal (with VM = ~10 %-40 %) is popularly used for heating in rural China in winter, the results of this study could assist to evaluate the climate and environmental impacts on the NACs emission from coal combustion on a regional scale. Finally, the results highlighted that replacements of bituminous by clear fuel (such as chunk or briquette anthracite) could reduce NACs emission effectively.

Molecular Composition, Seasonal Variation, and Size Distribution of n-Alkanes, PAHs, and Saccharides in a Medium-Sized City of Guanzhong Plain, Northwest China: Evaluation of Control Measures Executed in the Past Decade.

Baoji is a medium-sized city in the Guanzhong Plain of northwest China. The compositions of three important organic groups, namely n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and saccharides in atmospheric aerosol with different aerodynamic diameters in power were determined. Both seasonal and daily trends of the target organic chemical groups were demonstrated. The concentration levels of total quantified n-alkanes and saccharides in total suspended particles (TSP) in winter were 541 ± 39 and 651 ± 74 ng·m-3, respectively, much higher than those of the other three seasons. A high total quantified PAHs concentration level of 59.6 ± 6.4 ng·m-3 was also seen in wintertime. n-Alkanes showed a bimodal percent distribution in spring, autumn, and winter. Two peaks were found with the particle sizes of 0.7 µm < Dp < 2.1 µm and 3.3 µm < Dp < 4.7 µm, respectively. In summer, a unimodal was seen with a peak of 4.7 µm < Dp < 5.8 µm. Dehydrated saccharides and PAHs present a unimodal size distribution peaking at the aerodynamic diameters of 0.7 µm < Dp < 2.1 µm. In contrast to glucose and fructose, they mainly exist in the coarse mode particles and have the highest concentrations at aerodynamic diameters of 4.7 µm < Dp < 9.0 µm. The geometric mean diameters (GMD) of n-alkanes and saccharides of the fine particles in winter were higher than in the other seasons. Compared with the data in 2008, the fossil fuel-derived n-alkanes and PAHs in winter decreased by nearly an order of magnitude in 2017. Both the carbon preference index (CPI) of n-alkanes and the diagnostic ratios of PAHs suggest that coal combustion and vehicle exhaust were the major pollution sources of the organic groups in the two decades. It should be noted that the contribution of traffic emissions greatly increased from 2008 to 2017, consistently with a large raise of registered vehicles in Baoji city. The overall results confirm that the control measures conducted by the local government in the recent decade mitigated the air pollution in this city.

Volatile organic compounds at a roadside site in Hong Kong: Characteristics, chemical reactivity, and health risk assessment.

Volatile organic compounds (VOCs) and oxygenated VOCs (OVOCs) play important roles in atmospheric chemistry and are recognized as the major pollutants in roadside microenvironments of metropolitan Hong Kong, China. In this study, the ambient VOCs and OVOCs were intensively monitored at a roadside site in Hong Kong for one month during morning and evening rush hours. The emission characterizations, as well as ozone formation potentials (OFP) and hydroxyl radical (OH) loss rates (LOH) were determined. Results from the campaign showed that the average concentrations of detected VOCs/OVOCs ranged from 0.21 to 9.67 ppb, and higher toluene to benzene (T/B) ratio was observed during evening sections due to the variation of fuel types in vehicle fleets and mix of additional emission sources in this site. On average, OVOCs had much higher concentrations than the targeted VOC species. Acetone, formaldehyde, and acetaldehyde were the three most abundant species, while formaldehyde showed the highest contributions to both OFP (32.20 %) and LOH (16.80 %). Furthermore, potential health hazards with inhalation exposure to formaldehyde, acetaldehyde, propionaldehyde, methyl ethyl ketone (MEK), 1,3-butadiene, toluene, benzene, and acrylonitrile were found. These results reveal that it is imperative to implement efficient control measures to reduce vehicle emissions for both primary and secondary pollutants and to protect both roadside workers and pedestrians.

Associations of personal exposure to domestic heating and cooking fuel emissions and epidemiological effects on rural residents in the Fenwei Plain, China.

Solid fuel combustion for domestic heating in northern China in the wintertime is of great environmental and health concern. This study assesses personal exposure to particulate matter with different aerodynamic diameters and multiple gaseous pollutants from 123 rural residents in Yuncheng, the Fenwei Plain. The subjects are divided into groups based on the unique energy source applied, including biomass, coal, and electricity/no heating activities. The health effects of the exposures are expressed with four urinary biomarkers. The personal exposure levels to three different aerodynamic particle sizes (i.e., PM10, PM2.5, and PM1) of the electricity/no heating group are 5.1 % -12 % lower than those of the coal group. In addition, the exposure levels are 25 %-40 % lower for carbon monoxide (CO) and 10.8 %-20.3 % lower for ozone (O3) in the electricity/no heating group than the other two fuel groups. C-reactive protein (CRP) in the urine of the participants in biomass and coal groups is significantly higher than that in the electricity/no heating group, consistent with the observations on other biomarkers. Increases in 8-hydroxy-2 deoxyguanosine (8-OHdG), interleukin-8 (IL-8), and vascular endothelial growth factor (VEGF) are observed for the exposures to higher concentrations of air pollutants. For instance, PMs and nitrogen dioxide (NO2) show significant impacts on positive correlations with 8-OHdG and IL-8, while O3 positively correlates with CRP. PM1 exhibits higher effects on the biomarkers than the gaseous pollutants, especially on VEGF and IL-8. The study indicates that excessive use of traditional domestic solid fuels could pose severe health effects on rural residents. The promotion of using clean energy is urgently needed in the rural areas of northern China.

Pioneering observation of atmospheric volatile organic compounds in Hangzhou in eastern China and implications for upcoming 2022 Asian Games.

Understanding the emission sources of volatile organic compounds (VOCs) is critical for air pollution mitigation. Continuous measurements of atmospheric VOCs were conducted from January to February in Hangzhou in 2021. The average measured concentration of total VOCs (TVOCs) was 38.2 ± 20.9 ppb, > 42% lower than that reported by previous studies at the urban center in Hangzhou. The VOC concentrations and proportions were similar between weekdays and weekends. During the long holidays of the Spring Festival in China, the concentrations of TVOCs were ∼50% lower than those during the regular days, but their profiles showed no significant difference (p > 0.05). Further, we deduced that aromatics and alkenes were the most crucial chemicals promoting the formation of O3 and secondary organic aerosol (SOA) in Hangzhou. According to interspecies correlations, combustion processes and solvent use were inferred as major VOC emission sources. This study provides implications for air quality improvements before and during the upcoming Asian Games that will be hosted in Hangzhou in 2022.

Evidence of non-tailpipe emission contributions to PM2.5 and PM10 near southern California highways.

Particulate Matter (PM) concentrations near highways are influenced by vehicle tailpipe and non-tailpipe emissions, other emission sources, and urban background aerosols. This study collected PM2.5 and PM10 filter samples near two southern California highways (I-5 and I-710) over two weeks in winter 2020. Samples were analyzed for chemical source markers. Mean PM2.5 and PM10 concentrations were approximately 10-15 and 30 µg/m3, respectively. Organic matter, mineral dust, and elemental carbon (EC) were the most abundant PM components. EC and polycyclic aromatic hydrocarbons at I-710 were 19-26% and 47% higher than those at the I-5 sites, respectively, likely due to a larger proportion of diesel vehicles. High correlations were found for elements with common sources, such as markers for brake wear (e.g., Fe, Ba, Cu, and Zr) and road dust (e.g., Al, Si, Ca, and Mn). Based on rubber abundances, the contributions of tire tread particles to PM2.5 and PM10 mass were approximately 8.0% at I-5 and 5.5% at I-710. Two different tire brands showed significantly different Si, Zn, carbon, and natural rubber abundances.

Toxicological effects of fresh and aged gasoline exhaust particles in Hong Kong.

Exhaust emissions from gasoline vehicles are one of the major contributors to aerosol particles observed in urban areas. It is well-known that these tiny particles are associated with air pollution, climate forcing, and adverse health effects. However, their toxicity and bioreactivity after atmospheric ageing are less constrained. The aim of the present study was to investigate the chemical and toxicological properties of fresh and aged particulate matter samples derived from gasoline exhaust emissions. Chemical analyses showed that both fresh and aged PM samples were rich in organic carbon, and the dominating chemical species were n-alkane and polycyclic aromatic hydrocarbons. Comparisons between fresh and aged samples revealed that the latter contained larger amounts of oxygenated compounds. In most cases, the bioreactivity induced by the aged PM samples was significantly higher than that induced by the fresh samples. Moderate to weak correlations were identified between chemical species and the levels of biomarkers in the fresh and aged PM samples. The results of the stepwise regression analysis suggested that n-alkane and alkenoic acid were major contributors to the increase in lactate dehydrogenase (LDH) levels in the fresh samples, while polycyclic aromatic hydrocarbons (PAHs) and monocarboxylic acid were the main factors responsible for such increase in the aged samples.