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

Oxygenated volatile organic compounds in Beijing: Characteristics, chemical reactivity, and source identification

As important components of volatile organic compounds (VOCs), oxygenated VOCs (OVOCs) play a crucial role in the photochemical formation of ozone (O3), especially in the polluted areas in the North China Plain (NCP). However, their seasonal characteristics and sources are not well understood. In this study, one-year measurements of 10 typical OVOCs were conducted through proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) at an urban site (39.95° N, 116.32° E, 96 m a.s.l.) in Beijing. Aldehydes and alcohols were the most abundant types of OVOCs in the entire year, with mean concentrations of 16.3 ppbv and 15.9 ppbv, respectively, and mean proportions of 33.8 % and 32.4 % of the total. Formaldehyde and ethanol sustained the highest concentrations throughout the year, with mean annual concentrations of 13.5 ppbv and 10.8 ppbv, respectively. The results indicated that the concentrations of OVOCs were highest in the summer, along with the maximum O3-formation potentials and hydroxyl radical (•OH) reactivity values of 83.5 ppbv and 2.8 s-1, respectively. Results from the source apportionment of OVOCs based on multiple linear regression models indicated that secondary productions were the predominant source in summer. In particular, the secondary sources of aldehydes represented by CH2O and acetaldehyde accounted for 36.7 % and 51.4 % of the total, respectively. This study determined the concentrations and photochemical generation of OVOCs in different seasons, providing a basis for O3 pollution control in urban areas of Beijing.

Characterizing sources and health risks of airborne Carbonyl compounds in a subtropical coastal atmosphere in South China

Carbonyl compounds are critical air pollutants with adverse impacts on regional air quality and human health. This study presents a pioneering analysis of spatiotemporal distribution, source appointment, and health risk assessments of carbonyl compounds in the coastal marine atmosphere. By combining ship-borne and ground-based sampling followed with enhanced chemical analysis, 39 carbonyls were identified and quantified in the coastal Hong Kong. Carbonyl concentrations were generally higher in late summer/autumn with lower levels in winter, correlating with their secondary formation rates from precursors. Most species exhibited higher concentrations in open waters than in the fairway and sea channels, due to prominent photochemical formation from regional outflows in the Pearl River Estuary. In contrast, α, β-unsaturated aliphatic aldehydes and acetone were elevated in harbor areas, highlighting the influence of ship emissions on these compounds. Source analysis further indicated a notable contribution from ocean emissions to long-chain aldehydes (C ≥ 6), acetone and di-aldehydes. Health risk assessment demonstrated that carbonyl compounds pose substantial carcinogenic and non-carcinogenic risks to maritime workers and other exposed populations, even exceeding risks faced by road workers. These findings underscore the necessity of considering carbonyl compounds in occupational exposure risk assessments. Overall, this study provides a comprehensive overview of carbonyl compounds in the coastal marine atmosphere, shedding light on the interactions among ship emissions, ocean activities and coastal urban emissions on airborne carbonyls and emphasizing the associated health implications.

Insights into the source characterization, risk assessment and ozone formation sensitivity of ambient VOCs at an urban site in the Fenwei Plain, China

The ground-level O3 concentration has shown a deteriorating trend in the Fenwei Plain of China, which poses a greater challenge for formulating control strategies of O3 precursor (VOCs). To accurately control VOCs sources and effectively reduce O3 concentration from a seasonal perspective, online monitoring of 114 VOCs was conducted at Yuncheng Middle School Station from January 1, 2021 to December 31, 2021. The VOCs concentration showed a seasonal variation with the highest in winter and the lowest in summer. During the four seasons, alkanes (34.5-41.7 %) and OVOCs (36.6-46.9 %) were the most abundant species. The emission ratios of specific VOCs species indicated that vehicular exhaust, industrial source, and combustion were the major VOCs sources. The Positive Matrix Factorization (PMF) model identified that industrial source and secondary conversion were the main contributors in summer, while combustion and LPG/NG contributed more significantly in winter. The 2021-based VOCs emission inventory showed that the total VOCs emissions in the central urban area of Yuncheng was 8128.8 t, in which industrial process was the largest contributor. Alkanes, aromatics, and OVOCs accounted for 31.0 %, 25.8 %, and 25.7 % of the annual VOCs emission, respectively. In addition, the calculated relative incremental reactivity (RIR) values of O3 precursors demonstrated that alkenes and aromatics were the most sensitive groups to O3 formation during the four seasons. The ambient VOCs posed the non-carcinogenic risk across all seasons, which can be attributed to acrolein and three main sources (industrial source, secondary conversion, and combustion). However, ambient VOCs exposed to definite carcinogenic risks due to the appearance of 1,2-dichloroethane, 1,2-dichloropropane, and benzene, and the main risks arose from industrial source, vehicular exhaust, and solvent usage. These findings emphasize the necessity of undertaking scientific and systematic measures for priority species and control sources of VOCs emission.

Primary and oxidative source analyses of consumed VOCs in the atmosphere

Consumed VOCs are the compounds that have reacted to form ozone and secondary organic aerosol (SOA) in the atmosphere. An approach that can apportion the contributions of primary sources and reactions to the consumed VOCs was developed in this study and applied to hourly VOCs data from June to August 2022 measured in Shijiazhuang, China. The results showed that petrochemical industries (36.9 % and 51.7 %) and oxidation formation (20.6 % and 35.6 %) provided the largest contributions to consumed VOCs and OVOCs during the study period, whereas natural gas (5.0 % and 7.6 %) and the mixed source of liquefied petroleum gas and solvent use (3.1 % and 4.2 %) had the relatively low contributions. Compared to the non-O3 pollution (NOP) period, the contributions of oxidation formation, petrochemical industries, and the mixed source of gas evaporation and vehicle emissions to the consumed VOCs during the O3 pollution (OP) period increased by 2.8, 3.8, and 9.3 times, respectively. The differences in contributions of liquified petroleum gas and solvent use, natural gas, and combustion sources to consumed VOCs between OP and NOP periods were relatively small. Transport of petrochemical industries emissions from the southeast to the study site was the primary consumed pathway for VOCs emitted from petrochemical industries.

Tracking Source Variations of Inhalation Cancer Risks and Ozone Formation Potential in Hong Kong over Two Decades (2000-2020) Using Toxic Air Pollutant Monitoring Data

Toxic air pollutants (TAPs) are a class of airborne chemicals known or suspected to cause serious health issues. This study, applying positive matrix factorization and inhalation unit risk estimates of TAPs, quantifies the changes in significant sources contributing to inhalation cancer risks (ICRs) from 2000 to 2020 in Hong Kong, China. Total ICR decreased from 1701 to 451 cases per million between 2000-2004 and 2016-2020, largely attributed to the reduction in diesel particulate matter (DPM), gasoline and solvent use-related volatile organic compounds (VOCs), and coal/biomass combustion-related polycyclic aromatic hydrocarbons and metal(loid)s. The regional contribution of VOCs associated with industrial and halogenated solvent sources increased substantially, representing the largest non-DPM ICR contributor (37%) in 2016-2020, stressing the need for a more comprehensive risk evaluation across the fast-growing and densely populated Greater Bay Area (GBA). ICRs in Hong Kong and the GBA will likely remain over 100 cases per million by 2050. The contributions to ozone formation potential of VOC/carbonyl sources were quantified, which show a notable shift from being solvent/gasoline-dominant in 2000-2004 to being more evenly shared by various sources in 2016-2020. Establishing a similar TAP monitoring network in the GBA is anticipated to provide the monitoring data needed to facilitate the development of more informed air quality management strategies.

Pollution characteristics, source appointment and environmental effect of oxygenated volatile organic compounds in Guangdong-Hong Kong-Macao Greater Bay Area: Implication for air quality management

Same as other bay areas, the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) is also suffering atmospheric composite pollution. Even a series of atmospheric environment management policies have been conducted to win the "blue sky defense battle", the atmospheric secondary pollutants (e.g., O3) originated from oxygenated volatile organic compounds (OVOCs) still threaten the air quality in GBA. However, there lacks a systematic summary on the emission, formation, pollution and environmental effects of OVOCs in this region for further air quality management. This review focused on the researches related to OVOCs in GBA, including their pollution characteristics, detection methods, source distributions, secondary formations, and impacts on the atmosphere. Pollution profile of OVOCs in GBA revealed that the concentration percentage among total VOCs from Guangzhou and Dongguan cities exceeded 50 %, while methanol, formaldehyde, acetone, and acetaldehyde were the top four highest concentrated OVOCs. The detection technique on regional atmospheric OVOCs (e.g., oxygenated organic molecules (OOMs)) underwent an evolution of off-line derivatization method, on-line spectroscopic method and on-line mass spectrometry method. The OVOCs in GBA were mainly from primary emissions (up to 80 %), including vehicle emissions and biomass combustion. The anthropogenic alkenes and aromatics in urban area, and natural isoprene in rural area also made a significant contribution to the secondary emission (e.g., photochemical formation) of OVOCs. About 20 % in average of ROx radicals was produced from photolysis of formaldehyde in comparison with O3, nitrous acid and rest OVOCs, while the reaction between OVOCs and free radical accelerated the NOx-O3 cycle, contributing to 15 %-60 % cumulative formation of O3 in GBA. Besides, the heterogeneous reactions of dicarbonyls generated 21 %-53 % of SOA. This review also provided suggestions for future research on OVOCs in terms of regional observation, analytical method and mechanistic study to support the development of a control and management strategy on OVOCs in GBA and China.

Volatile organic compounds exposure associated with depression among U.S. adults: Results from NHANES 2011-2020

Volatile organic compounds (VOCs) are important contributors to air pollution. VOCs exposure was associated with various human diseases. Depression is one of the most prevalent mental disorders and poses a serious mental health burden. Although VOCs are neurotoxic and can damage the central nervous system, the association between VOCs exposure and depression remains obscure. Based on data from the National Health and Nutrition Examination Survey, we included 5676 adult individuals and 15 major components of urinary volatile organic compound metabolites (mVOCs). We comprehensively evaluated the potential association between each single urinary mVOC exposure and depressive symptoms using binary logistic and restricted cubic spline regression, whereas the weighted quantile sum regression and least absolute shrinkage and selection operator regression model were used to explore the mixture co-exposure association. The results indicated significantly higher mean concentrations of the 11 urinary mVOC components in the depression group than that in the non-depression group. And 12 mVOC components had a significantly positive association with depression. The overall effect of all 15 mVOCs components was also significantly positive. The corresponding odds ratio was 1.56 (95%CI: 1.2-2.03) in the categorical variable model and the regression coefficient was 0.36 (95%CI: 0.12-0.6) in the numerical variable model. Five urinary mVOCs (URXCYM, URXPHG, URX34 M, URXMB3, and URXAMC) were identified as the most relevant components associated with depression, with 89.06% total weights in the categorical variable model and 89.39% in the numerical variable model. The mVOCs were the biomarkers of VOCs, their concentrations in urine could specifically represent the contents of their metabolic parents in the human body. Considering that the metabolic parents of the above five mVOCs were predominantly acrylonitrile, toluene, styrene, acrylamide, 1,3-Butadiene, and xylenes, our results further indicated that exposure to these VOCs was closely related to depression, and more attention should be paid to the mental health risks of VOCs exposure.

Origin and transformation of volatile organic compounds at a regional background site in Hong Kong: Varied photochemical processes from different source regions

Volatile organic compounds (VOCs) are important gaseous constituents in the troposphere, impacting local and regional air quality, human health, and climate. Oxidation of VOCs, with the participation of nitrogen oxides (NOx), leads to the formation of tropospheric ozone (O3). Accurately apportioning the emission sources and transformation processes of ambient VOCs, and effectively estimation of OH reactivity and ozone formation potential (OFP) will play an important role in reducing O3 pollution in the atmosphere and improving public health. In this study, field measurements were conducted at a regional background site (Hok Tsui; HT) in Hong Kong from October to November 2020 with proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS). VOC data coupled with air mass back trajectory cluster analysis and receptor modelling were applied to reveal the pollution pattern, emission sources and transformation of ambient VOCs at HT in autumn 2020. Seven sources were identified by positive matrix factorization (PMF) analysis, namely vehicular + industrial, solvent usage, primary oxygenated VOCs (OVOCs), secondary OVOCs 1, secondary OVOCs 2 (aged), biogenic emissions, and background + biomass burning. Secondary formation and vehicular + industrial emissions are the vital sources of ambient VOCs at HT supersite, contributing to 20.8 % and 46.7 % of total VOC mixing ratios, respectively. Integrated with backward trajectory analysis and correlations of VOCs with their oxidation products, short-range transport of air masses from inland regions of southeast China brought high levels of total VOCs but longer-range transport of air masses brought more secondary OVOCs in aged air masses. Photolysis of OVOCs was the most important contributor to OH reactivity and OFP, among which aldehyde was the dominant contributor. The results of this study highlight the photochemical processing of VOCs from different source regions which should be considered in strategy making for pollution reduction.