Suburban Site Research Articles

Carbonyl Compounds Observed at a Suburban Site during an Unusual Wintertime Ozone Pollution Event in Guangzhou

Carbonyl compounds are important oxygenated volatile organic compounds (VOCs) that play significant roles in the formation of ozone (O3) and atmospheric chemistry. This study presents comprehensive field observations of carbonyl compounds during an unusual wintertime ozone pollution event at a suburban site in Guangzhou, South China, from 19 to 28 December 2020. The aim was to investigate the characteristics and sources of carbonyls, as well as their contributions to O3 formation. Formaldehyde, acetone, and acetaldehyde were the most abundant carbonyls detected, with average concentrations of 7.11 ± 1.80, 5.21 ± 1.13, and 3.00 ± 0.94 ppbv, respectively, on pollution days, significantly higher than those of 2.57 ± 1.12, 2.73 ± 0.88, and 1.10 ± 0.48 ppbv, respectively, on nonpollution days. The Frame for 0-D Atmospheric Modeling (F0AM) box model simulations revealed that local production accounted for 62–88% of observed O3 concentrations during the pollution days. The calculated ozone formation potentials (OFPs) for various precursors (carbonyls and VOCs) indicated that carbonyl compounds contributed 32.87% of the total OFPs on nonpollution days and 36.71% on pollution days, respectively. Formaldehyde, acetaldehyde, and methylglyoxal were identified as the most reactive carbonyls, and formaldehyde ranked top in OFPs, and it alone contributed 15.92% of total OFPs on nonpollution days and 18.10% of total OFPs on pollution days, respectively. The calculation of relative incremental reactivity (RIR) indicates that ozone sensitivity was a VOC-limited regime, and carbonyls showed greater RIRs than other groups of VOCs. The model simulation showed that secondary formation has a significant impact on formaldehyde production, which is primarily controlled by alkenes and biogenic VOCs. The characteristic ratios and backward trajectory analysis also indicated the indispensable impacts of local primary sources (like industrial emissions and vehicle emissions) and regional sources (like biomass burning) through transportation. This study highlights the important roles of carbonyls, particularly formaldehyde, in forming ozone pollution in megacities like the Pearl River Delta region.

The Paris low-level jet during PANAME 2022 and its impact on the summertime urban heat island

Abstract. The low-level jet (LLJ) and the urban heat island (UHI) are common nocturnal phenomena. While the UHI has been studied extensively, interactions of the LLJ and the urban atmosphere in general (and the UHI in particular) have received less attention. In the framework of the PANAME (PAris region urbaN Atmospheric observations and models for Multidisciplinary rEsearch) initiative in the Paris region, continuous profiles of horizontal wind speed and vertical velocity were recorded with two Doppler wind lidars (DWLs) – for the first time allowing for a detailed investigation of the summertime LLJ characteristics in the region. Jets are detected for 70 % of the examined nights, often simultaneously at an urban and a suburban site, highlighting the LLJ regional spatial extent. Emerging at around sunset, the mean LLJ duration is ∼ 10 h, the mean wind speed is 9 m s−1, and the average core height is 400 m above the city. The temporal evolution of many events shows signatures that indicate that the inertial oscillation mechanism plays a role in the jet development: a clockwise veering of the wind direction and a rapid acceleration followed by a slower deceleration. The horizontal wind shear below the LLJ core induces variance in the vertical velocity (σw2) above the urban canopy layer. It is shown that σw2 is a powerful predictor for regional contrast in air temperature, as the UHI intensity decreases exponentially with increasing σw2 and strong UHI values only occur when σw2 is very weak. This study demonstrates how DWL observations in cities provide valuable insights into near-surface processes relevant to human and environmental health.

West Nile virus in adults and larvae of Culiseta longiareolata and Culex hortensis (Diptera: Culicidae) captured in Hamedan, western Iran

West Nile virus (WNV) is an emerging arbovirus transmitted by mosquitoes. Although it is considered the most widespread mosquito-borne arbovirus in Iran, vectors of this zoonotic pathogen remain unknown in many regions. This study aimed to assess the presence of WNV in mosquitoes collected in the western city of Hamedan in 2022. Adult mosquitoes were captured using light traps, and mosquito larvae were collected by dipping technique from 45 diverse habitats, including urban, suburban, and rural sites. Specimens were identified and pooled into 69 batches based on their species for viral RNA extraction and Real-Time PCR. In total, 3243 mosquitoes (2209 larvae and 1034 adults) were captured and identified as Culiseta longiareolata, Culex hortensis, Anopheles maculipennis s.l., Culex theileri, Culex pipiens, Anopheles claviger, and Anopheles superpictus s.l. in decreasing order. Molecular screening revealed seven WNV-positive pools of Culiseta longiareolata and Culex hortensis in rural (n = 5) and urban areas (n = 2). Detection of WNV RNA indicates active circulation in mosquitoes and risk of transmission to humans and animals in Hamadan. These findings identify putative vectors in Hamadan, though vectors likely vary regionally in Iran. Further surveillance is needed to elucidate local WNV epidemiology and transmission dynamics fully. Nonetheless, this study provides important baseline evidence of WNV activity to guide prevention strategies in this area.

Causes of the unremitting high ambient levels of PM10 in a suburban background site in NE Spain

Atmospheric PM10 and benzo(a)pyrene (BaP) concentrations in Manlleu (NE Spain) have remained high from 2008 to 2023, frequently exceeding EU limit/target values, and reaching BaP levels up to six times higher than urban averages in Spain. Furthermore, PM speciation campaigns were carried out in 2013, 2014–2015, 2016–2017 and 2021–2022. Chemical mass closure for autumn-winter showed a consistent PM10 composition for the different PM speciation campaigns, comprising 46–53% organic matter (OM), 18–26% secondary inorganic aerosol (SIA), 13–23% mineral matter (MM), and 5–9% elemental carbon (EC). Trend analysis revealed very light decrease and constant concentrations for PM10 and BaP, respectively over the study period, emphasizing the need for compliance with current and forthcoming EU air quality directives, the last aiming to halve PM10 limit values. Source apportionment of samples of the sporadic campaigns identified biomass burning (BB, 17.5 μg m−3, 48%) and MM and industry (16.3 μg m−3, 44%) as the main autumn-winter PM10 contributors, with high SIA concentrations attributed to several factors, including high ammonia (NH3) emissions. Local topography and meteorological conditions contribute to aggravate PM10 pollution. While metal concentrations have decreased since 2013, suggesting reduced industrial emissions, persistently high OM and EC concentrations indicate ongoing issues with BB emissions from domestic, commercial, and agricultural sources. Online analysis of black carbon (BC) and non-refractory PM1 components during winter 2016–2017 confirmed domestic and commercial BB as the primary sources of the BB contributions. These findings highlight the need of the implementation of more effective measures in reducing BB and agricultural/farming NH3 emissions. This study highlights the relevance of these issues for similar towns, the probable unremitting problem over the last decade, and the necessity of enhanced monitoring in small cities and policy actions to meet air quality standards under the new EU directive.

Phantom Writing

In this visual essay I present a body of artistic work done within informal urban and suburban heritage sites in Kyoto. Through the media of text, photography, film and site-specific painting, my works from the cycle Spirit Grounds engage with these sites involving material physical aspects as well as beliefs, fictions, and more-than-human beings. Building upon this, I propose ‘phantom writing’ or ‘phantasmography’ as a situated, multidisciplinary and multisensory approach aimed at understanding and designing contemporary places, landscapes and environments, acknowledging and mediating the agency of diverse phantoms and phantasms.

Investigating the role of photochemistry and impact of regional and local contributions on gaseous pollutant concentrations (NO, NO2, O3, CO, and SO2) at urban and suburban sites

Gaseous pollutant concentrations were monitored for one year in urban (NO, NO2, O3, CO, and SO2) and suburban (NO, NO2, and O3) sites. Common characteristics were identified at both sites, such as higher concentrations during typical winter months for all pollutants except O3. Increased NO, NO2, CO and SO2 concentrations during wintertime were linked to residential heating emissions, with pairwise correlations showing CO as marker for the study site. O3 production was lower in wintertime but higher in summertime at both sites based on its seasonal cycle and the impact of sunlight. Furthermore, diurnal variations showed that traffic emissions during rush hours most profoundly affected CO and NO. Nevertheless, NOx were characteristically higher at the urban site based on the burdened environment, whereas O3 was higher at the suburban site due to the lower destruction rates. O3 was the dominant oxidant at both sites, with a linear regression between OX and NOx revealing a negative relationship. This observation suggested a dominant regional contribution to oxidant concentrations. In addition, abnormally high O3 concentrations in relation to the season were reported for the first time at the study sites. Elevated concentrations were measured in parallel with Sahara dust events indicating noteworthy atmospheric conditions that require further assessment. Other O3 burdened periods were driven by regional transport of polluted plumes from the northeast. Lastly, nocturnal increases in O3 were observed and associated with enhanced vertical mixing.

Role of Organic Vapor Precursors in Secondary Organic Aerosol Formation: Concurrent Observations of IVOCs and VOCs in Guangzhou

AbstractSecondary organic aerosol (SOA) formed through the atmospheric transformation of organic vapors constitutes a significant portion of fine particulate matter or PM2.5. While recent laboratory studies underscore the importance of intermediate‐volatility organic compounds (IVOCs) as key precursors to SOA, field observations that recognize the role of both volatile organic compounds (VOCs) and IVOCs in SOA formation remain scarce. In this study, we conducted concurrent measurements of VOCs and IVOCs in ambient air at urban and suburban sites in Guangzhou during a PM2.5 pollution event in winter 2021. The results reveal that between 12:00–15:00 local time, the photochemically adjusted initial concentrations of VOCs at both sites were approximately 7 times higher than that of IVOCs. However, the SOA formation potential (SOAFP) of primary hydrocarbon IVOCs exceeded that of VOCs by over 3–4 times. Receptor modeling results further indicated that while ship emissions contributed to less than 10% of the C2–C22 primary hydrocarbons concentration (VOCs + primary carbonaceous IVOCs), they accounted for the most significant source (approximately 40%) of SOA formation. This study highlights the substantial role of IVOCs in SOA formation and emphasizes the importance of future PM2.5 pollution control measures targeting major IVOCs contributors, such as ship emissions in harbor cities.

Ozone response to precursors changes in the Chengdu-Chongqing economic circle, China, from satellite and ground-based observations

Ozone (O3) pollution has become a noticeable problem in the Chengdu-Chongqing Economic Circle in China. The April–September MDA8 O3 level increases significantly by 2.26 μg m−3 year−1 from 2015 to 2023, with meteorological factors occupying merely 18 % in line with multivariate linear regression. To reveal the impact of anthropogenic emissions on O3 increase, O3 production sensitivity is accurately diagnosed by deriving localized thresholds for satellite formaldehyde (HCHO) to NO2 ratio and validated by in-situ measurements and observation-based model. Tracking volatile organic compounds (VOCs) and NOx through satellite HCHO and NO2, the O3 responses to precursor changes are assessed for long-term and special cases, and appropriate precursor reduction ratios are inferred. The results present that the transition range of satellite HCHO/NO2 from VOC-limited to NOx-limited in the region ranges from 2.7 to 4.3. The VOC-limited regime is concentrated in the urban areas of Chongqing and Chengdu as well as the central of the neighboring cities such as Deyang, Mianyang, and Meishan. The relative incremental reactivity from in-situ observations and box model at three sites in August 2019 demonstrates that O3 is most sensitive to anthropogenic VOC at urban and suburban sites, consistent with satellite results. Satellite and surface NO2 decrease at an annual rate of −2.1 % and − 2.9 % between 2015 and 2023, with larger decreases in Chengdu and Chongqing. In contrast, the trend of satellite HCHO is insignificant, indicating effective reduction in NOx but no significant reduction in VOC. This inappropriate reduction results in an increase in urban O3. The three short-term cases further validate the need for synergistic NOx and VOC reductions. Based on the relationship between O3 and satellite NO2 and HCHO, the minimum and optimal reduction ratios of VOC to NOx are 0.4:1 and 2.4:1 for the entire region, with higher ratios in Chengdu and Chongqing.

Effect of geographical parameters on PM10 pollution in European landscapes: a machine learning algorithm-based analysis

BackgroundPM10, comprising particles with diameters of 10 µm or less, has been identified as a significant environmental pollutant associated with adverse health outcomes in European cities. Understanding the temporal variation of the relationship between PM10 and geographical parameters is crucial for sustainable land use planning and air quality management in European landscapes. This study utilizes Conditional Inference Forest modeling and partial correlation to examine the impact of geographical factors on monthly average concentrations of PM10 in European suburban and urban landscapes during heating and cooling periods. The investigation focuses on two buffer zones (1000 m and 3000 m circle radiuses) surrounding 1216 European air quality monitoring stations.ResultsResults reveal importance and significant correlations between various geographical variables (soil texture, land use, transportation network, and meteorological) and PM10 quality on a continental scale. In suburban landscapes, soil texture, temperature, roads, and rail density play pivotal roles, while meteorological variables, particularly monthly average temperature and wind speed, dominate in urban landscapes. Urban sites exhibit higher R-squared values during both cooling (0.41) and heating periods (0.61) compared to suburban sites (cooling period R-squared: 0.39; heating period: R-squared: 0.51), indicating better predictive performance likely attributed to the less heterogeneous land use patterns surrounding urban PM10 monitoring sites.ConclusionThe study underscores the importance of investigating spatial and temporal dynamics of geographical factors for accurate PM10 air quality prediction models in European urban and suburban landscapes. These findings provide valuable insights for policymakers, urban planners, and environmental scientists, guiding efforts toward sustainable and healthier urban environments.

A Comparison of Regression Methods for Inferring Near‐Surface NO2 With Satellite Data

AbstractNitrogen dioxide (NO2) is an atmospheric pollutant emitted from anthropogenic and natural sources. Human exposure to high NO2 concentrations causes cardiovascular and respiratory illnesses. The Environmental Protection Agency operates ground monitors across the U.S. which take hourly measurements of NO2 concentrations, providing precise measurements for assessing human pollution exposure but with sparse spatial distribution. Satellite‐based instruments capture NO2 amounts through the atmospheric column with global coverage at regular spatial resolution, but do not directly measure surface NO2. This study compares regression methods using satellite NO2 data from the TROPospheric Ozone Monitoring Instrument (TROPOMI) to estimate annual surface NO2 concentrations in varying geographic and land use settings across the continental U.S. We then apply the best‐performing regression models to estimate surface NO2 at 0.01° by 0.01° resolution, and we term this estimate as quasi‐NO2 (qNO2). qNO2 agrees best with measurements at suburban sites (cross‐validation (CV) R2 = 0.72) and away from major roads (CV R2 = 0.75). Among U.S. regions, qNO2 agrees best with measurements in the Midwest (CV R2 = 0.89) and agrees least in the Southwest (CV R2 = 0.65). To account for the non‐Gaussian distribution of TROPOMI NO2, we apply data transforms, with the Anscombe transform yielding highest agreement across the continental U.S. (CV R2 = 0.77). The interpretability, minimal computational cost, and health relevance of qNO2 facilitates use of satellite data in a wide range of air quality applications.

Characteristics and Influence of Atmospheric VOCs in Ozone Formation Potential in Suburb of Shanghai During Summer

To help promote ozone pollution control and understand the influence of atmospheric volatile organic compounds （VOCs） on O3 during the summer ozone pollution season, the analyses of variation characteristics and ozone formation potentials of VOCs during O3 pollution episodes were carried out based on the online monitoring data of VOCs and O3, as well as the meteorological parameters in the suburban site of Shanghai. The impact of key meteorological factors and regional transport on O3 and VOCs was investigated. The results showed that the mean value of atmospheric φ（VOCs） during summer in the suburban area of Shanghai was （20.91 ± 9.82）×10-9, and the largest proportion of each component was with alkanes and OVOCs, both of which were 30.2%. The mean value of φ（VOCs） on O3 polluted days was （23.84 ± 9.69）×10-9, which was 28.1% higher than that on clean days. The OFP of VOCs on polluted days was 126.92 μg·m-3, which was 31.9% higher than that on clean days. The contribution of olefins to OFP accounted for a significant increase, and species such as propylene and acetone were the most significant compared to on clean days, indicating that these components and species need to be the focus of mitigation. The variation characteristics of the ratio of ethane to acetylene （E/E） and the ratio of m/p-xylene to ethylbenzene（X/E） indicated that there was a significant regional transport influence of the summer air masses in the suburban area of Shanghai, and it occurred mainly in the afternoon and at night. The results of the pollution rose diagram and the backward trajectory of air masses indicated that air masses from the south and southwest directions had the greatest influence on the transport of VOCs in suburban Shanghai. In particular, it is necessary to focus on controlling olefin and OVOCs from southern air masses and aromatic hydrocarbons from southwestern air masses.

Ozone production sensitivity analysis for the Chengdu Plain Urban Agglomeration based on a multi-site and two-episode observation

Chengdu Plain Urban Agglomeration (CPUA) is one of the most serious areas suffering from ozone pollution in China. A comprehensive field observation focused on the ozone production rate and its sensitivity was conducted at CPUA in the summer of 2019. Six sampling sites were set and two ozone pollution episodes were recognized. The daily maximum 8-h average (MDA8) O3 concentration reached 137.9 ppbv in the urban sites during the ozone pollution episode. Peak concentration of O3 was closely related to intense solar radiation, high temperatures, and precursor emissions. The OH-HO2-RO2 radical chemistry and ozone production rate (P(O3)) were calculated using an observation-based model (OBM). The daily peak OH concentration varied in the range of 3-13 × 106 molecules cm−3, and peak HO2 and RO2 were in the range of 2–14 × 108 molecules cm−3 during ozone pollution episodes. During the ozone pollution episode, the average maximum of P(O3) in suburban sites (about 30 ppbv h-1.) was compared with urban sites, and the maximum of P(O3) was 18 ppbv h-1 in rural sites. The relative incremental reactivity (RIR) results demonstrate that it was a VOCs-limited regime in the central urban area of Chengdu, with NOx suppression effect in some regions. In the southern neighboring suburb of Chengdu, it was VOCs-limited as well. However, the northern suburban area was a transition region. In the remote rural areas of the southern CPUA, it was highly NOx-limited. Local ozone production driven by the photochemical process is crucial to the ozone pollution formation in CPUA. The geographically differentiated recognition of the ozone regime found by this study can help to tailor control strategies for local conditions and avoid the negative effects of a one-size-fits-all approach.

Characteristics and Source Apportionment of Volatile Organic Compounds in a Coastal Industrial Area: A Case Study in the Yangtze River Delta of China.

In recent years, the coastal area in East China has experienced elevated volatile organic compounds (VOCs) levels during specific periods. VOCs have become one of the major atmospheric pollutants in these areas. In this study, 64 compounds including alkanes, alkenes, halohydrocarbons, aromatics, and oxygenated VOCs (OVOCs) were obtained by the TO-15 method through a 12-month campaign in industrial, urban and suburban areas in the Yangtze River Delta of China. The overall trends of total VOC (TVOC) concentrations at eight sampling sites were as follows: winter > autumn > spring > summer. The proportion of VOC categories was various at industrial sites, while OVOCs and halohydrocarbons had high proportions at urban sites and suburban sites, respectively. Coating, vehicle emission, petrochemical source, industrial source, and gasoline volatilization were identified as the major VOC emission sources by the positive matrix factorization model. Petrochemical and coating sources were the prime VOC sources at industrial sites. Aromatics contributed the most ozone formation potential at industrial sites, while OVOCs provided the main contributions at both urban and suburban sites during four seasons. According to the health risk assessment, a high probability of non-carcinogenic risk existed at three industrial sites. Special attention should be given to certain VOCs, such as acrolein and 1,2-dibromoethane in industrial areas.

Going urban: variation in personality traits of an invasive species along an urbanization gradient

Abstract The fast-growing expansion of urban areas pose severe pressures on wildlife. However, some generalist native mammals thrive in urbanized landscapes, while invasive alien species (IAS) are often more abundant in cities than in rural habitats. Variation in phenotypes—such as differences in personality traits—can influence the probability to colonize anthropized areas, especially in the case of IAS where certain traits are related to invasion success. Here, we investigated the expression of activity, exploration, and social tendency in the invasive alien Eastern Gray Squirrel (Sciurus carolinensis) in replicated study sites along a rural–urban gradient in Northern Italy. Personality traits expression was estimated using an open field test (OFT) followed by a mirror image stimulation (MIS) test. We found that squirrels were more active in urban than in suburban and rural sites, and behaved more sociable in urban than in suburban sites. Conversely, exploration did not differ along the gradient. Results also reveal the presence of a behavioral syndrome: activity (OFT), social tendency, and activity–exploration (MIS). We suggest that variation in activity level and social behavior in urban habitats could favor some species to respond positively to urbanization. This study sheds light on the underexplored personality–urbanization relationship in IAS, helping to understand the complex process of invasion.

Study on the Strength of Rural Tourism Operators’ Willingness to Carbon Offset and Its Influencing Mechanisms

Tourism operators generate carbon emissions during their operations, and their environmental responsibility behaviors, such as carbon offsetting, significantly impact the ecological environment of tourist sites. Understanding the operators’ willingness to engage in carbon offsetting and the factors influencing this willingness is crucial for achieving the “dual carbon” goals and promoting sustainable growth in China’s tourism sector. This study collected 746 offline questionnaires from operators at rural tourism sites across 100 counties and districts in Jiangxi Province. It empirically analyzed their willingness to participate in carbon offsetting, comparing various factors such as the strength of willingness, spatial differences, and distinctions between all-for-one tourism counties and non-all-for-one tourism counties, as well as suburban, outer suburban, and remote tourism sites. Using the value–belief–norm theory and the theory of planned behavior, a structural equation model was developed to comprehensively examine the operators’ willingness and its influencing mechanisms. The structural statistical analysis revealed that the integrated model effectively predicted rural tourism operators’ willingness to participate in carbon offsetting. The results showed that, except for Hypothesis 6, all suggested correlations between the variables were significant. Value perception had a significantly positive effect on participants’ desire to engage in carbon offsetting. This research provides various theoretical and practical implications for local authorities regarding rural tourism operators, advancing the incentive for carbon offsetting and sustainable tourism development.

Study on the temporal and spatial distribution of Culex mosquitoes in Hanoi, Vietnam

Arboviruses transmitted by mosquitoes, including Japanese encephalitis virus (JEV), present a substantial global health threat. JEV is transmitted by mosquitoes in the genus Culex, which are common in both urban and rural areas in Vietnam. In 2020, we conducted a 1-year survey of Culex mosquito abundance in urban, suburban, and peri-urban areas of Hanoi using CDC-light traps. Mosquitoes were identified to species and sorted into pools based on species, sex, and trap location. The mosquito pools were also investigated by RT-qPCR for detection of JEV. In total, 4829 mosquitoes were collected over a total of 455 trap-nights, across 13 months. Collected mosquitoes included Culex, Aedes, Anopheles, and Mansonia species. Culex mosquitoes, primarily Cx. quinquefasciatus, predominated, especially in peri-urban areas. Most Culex mosquitoes were caught in the early months of the year. The distribution and abundance of mosquitoes exhibited variations across urban, suburban, and peri-urban sites, emphasizing the influence of environmental factors such as degree of urbanization, temperature and humidity on Culex abundance. No JEV was detected in the mosquito pools. This study establishes baseline knowledge of Culex abundance and temporal variation, which is crucial for understanding the potential for JEV transmission in Hanoi.

Characterization of atmospheric nitroaromatic compounds in Southwest China by direct injection liquid chromatography-tandem mass spectrometry analysis of aerosol extracts

Nitroaromatic compounds (NACs) in ambient particles are of great concern due to their adverse effects on human health and climate. However, investigations on the characteristics and potential sources of NACs in Southwest China are still scarce. In this study, a field sampling campaign was carried out in the winter of 2022 at a suburban site in Mianyang, Southwest China. A direct injection liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to rapidly determine 10 NACs in fine particulate matter (PM2.5) extracts. The method was sensitive for the quantification of the NACs, with a limit of quantification (LOQ) in the range of 0.092–0.52 ng mL−1. Then, the developed method was applied to determine the concentrations of nitrophenols (NPs), nitrocatechols (NCs), nitrosalicylic acids (NSAs), and nitronaphthol in PM2.5 in Mianyang. The average concentration of total NACs was 78.2 ± 31.2 ng m−3, with daily concentrations ranging from 20.7 to 127.9 ng m−3. Among the measured NACs, 4-nitrocatechol was the most abundant, accounting for 57.8% of the NACs in winter. The five NPs compounds together contributed to 14% of the NACs, which was lower than in other Chinese cities due to the warm climate in winter in Southwest China. NSAs and nitronaphthol each accounted for less than 5% of the NACs. Three major sources of NACs were identified based on the principal component analysis, including vehicle emissions, biomass burning, and secondary formation. The significant correlation between individual NACs and NO2 supported their secondary formation sources. The good correlation between NPs and cloud amount further suggested that gas-phase oxidation was the possible NPs formation mechanism. Our findings revealed the important role of nitrocatechols in NACs in Southwest China, implying that more measures should be taken to control biomass burning and aromatic volatile organic compounds emissions to reduce the level of NACs.

Comprehensive measurement of carbonyls in Lhasa, Tibetan Plateau: Implications for strong atmospheric oxidation capacity

Carbonyls are ubiquitous in the troposphere and play a crucial role in atmospheric oxidation capacity (AOC), particularly in photochemistry-active regions such as the Tibetan Plateau (TP). However, the composition and evolution of carbonyls over the TP is still poorly understood due to a lack of comprehensive observations and modelling. Here, we conducted an intensive field measurement of 37 carbonyls and their precursors at a suburban site in Lhasa during summer 2022. Markedly higher levels of carbonyls (7.24 ± 3.83 ppbv) were found during ozone pollution episodes, with 36 % higher than those during non-episodes. Formaldehyde was the most abundant carbonyl (38 %), which primarily originating from photochemical secondary formations. Simulations using the Rapid adaptive Optimization Model for Atmospheric Chemistry (ROMAC) indicated strong AOC in Lhasa, with the daytime maximum of ·OH and ·HO2 of 9.8 × 106 and 4.2 × 108 molecules cm−3, respectively, which were even higher than that in most of the megacities in China. Notably, AOC significantly enhanced with the increasing carbonyls during the episodes, with the concentrations of ·OH and ·HO2 were boosted 21 % and 67 % than those during non-episodes, respectively. Budget analysis revealed that the ·HO2 + NO (88 %) and ·OH + VOC (74 %) pathways dominated the generation and loss of ·OH, respectively. And for ·HO2, they were ·RO2 + NO (67 %) and ·HO2 + NO (83 %). This study provides valuable insights into the strong AOC in the ecologically-fragile and climate-sensitive TP region, and highlighted the crucial role of anthropogenic–biogenic interactions in the active photochemistry of TP.

Different formation pathways of nitrogen-containing organic compounds in aerosols and fog water in northern China

Abstract. While aqueous-phase processing is known to contribute to the formation of nitrogen-containing organic compounds (NOCs), the specific pathways involved remain poorly understood. In this study, we aimed to characterize the NOCs present in both pre-fog aerosols and fog water collected at a suburban site in northern China. Fourier-transform ion cyclotron resonance mass spectrometry was utilized to analyze the molecular composition of NOCs in both negative and positive modes of electrospray ionization (ESI− and ESI+). In both pre-fog aerosols and fog water samples, NOCs constituted a significant portion, accounting for over 60 % of all assigned formulas in ESI− and more than 80 % in ESI+. By comparing the molecular composition of NOCs originating from biomass burning, coal combustion, and vehicle emissions, we identified that 72.3 % of NOCs in pre-fog aerosols were attributed to primary anthropogenic sources (pNOCs), while the remaining NOCs were categorized as secondary NOCs formed within the aerosols (saNOCs). Unique NOCs found in fog water were classified as secondary NOCs formed within the fog water (sfNOCs). Through a comprehensive “precursor–product pair” screening involving 39 reaction pathways, we observed that the nitration reaction, the amine pathway, and the intramolecular N-heterocycle pathway of NH3 addition reactions contributed 43.6 %, 22.1 %, and 11.6 % of saNOCs, respectively. In contrast, these pathways contributed 26.8 %, 28.4 %, and 29.7 % of sfNOCs, respectively. This disparity in formation pathways is likely influenced by the diverse precursors, the aqueous acidity, and the gas-phase species partitioning. Correspondingly, saNOCs were found to contain a higher abundance of carbohydrate-like and highly oxygenated compounds with two nitrogen atoms compared to pNOCs. Conversely, sfNOCs exhibited a higher content of lipid-like compounds with fewer oxygen atoms. These results underscore the distinct secondary processes contributing to the diversity of NOCs in aerosols and fog water, which may lead to their different climate effects.

Spatiotemporal variations of atmospheric mercury at urban and suburban areas in Southern Vietnam megacity: A preliminary year-round measurement study

Atmospheric mercury (Hg) pollution studies in peninsular Southeast Asia (PSEA) are currently experiencing shortage on spatiotemporal coverage due to limited observation data. Therefore, our study provided year-round (May 2022–April 2023) atmospheric Hg data at two urban and one suburban site in Ho Chi Minh City (HCMC) Vietnam - a megacity in PSEA. Higher total gaseous Hg (TGM) levels at 2 urban sites of 2.49 ± 0.86 ng m−3 (Nguyen Van Cu) and 2.12 ± 0.49 ng m−3 (Linh Trung) were observed as compared to the suburban site of 1.76 ± 0.50 ng m−3 (Can Gio) which suggests the influence of anthropogenic Hg sources. Higher TGM concentration in October 2022–January 2023 as opposed to May 2022–September 2022 at all 3 sites reflected the influence of abrupt change in air mass origins and transport pathways in southern Vietnam. Backward trajectories (BWTs) and concentration-weighted trajectory (CWT) models further suggested East Asian outflow from northeast (NE) direction as a prominent TGM source in HCMC. Our two case studies in June and December 2022 helped to distinguish the impacts of local accumulation besides long-range atmospheric Hg transport towards TGM levels in HCMC. We also attempted to address TGM public health concerns wherein a minimal hazard quotient (HQ < 1) implied insignificant Hg health risk via inhalation pathways. Our study strives to offer crucial information to fill the Hg data gap as well as seeks to explore the impact of monsoon drives on Hg pollution in the PSEA region.