Composition and chemical processing of volatile organic compounds in boundary layer polluted plumes: Insights from an airborne Q-PTR-MS on-board the French ATR-42 aircraft.

Over the last decade, the French ATR-42 research aircraft explored contrasting polluted plumes in the Paris megacity, the North-West Mediterranean Basin (WMB) and South West Africa (SWA) in the framework of the MEGAPOLI, ChArMEx/SAFMED and DACCIWA international projects, respectively. Major VOCs were measured by a high-sensitivity airborne Quadrupole Proton Transfer Reaction Mass Spectrometer (Q-PTR-MS), showing a robust and consistent response. Regardless of the location, the air mass composition is dominated by oxygenated VOC (OVOC: methanol, formaldehyde, acetaldehyde, acetone and isoprene oxidation products), which explain 70 % of the total VOC burden measured by the Q-PTR-MS. The distribution between OVOC, anthropogenic AVOC and biogenic BVOC is consistent between the three regions. The calculated OH loss rates (12 s-1) and ozone-forming potential (1200 OFP-relative ppb) are three times higher in the SWA plumes. These values are consistent with the calculated and measured reactivities at the ground. The reactivity of the plumes is by far dominated by biogenic BVOC. The chemical processing of VOC was examined by establishing various metrics linking Δ[O/VOC] (VOC or oxygenated VOC), plume dilution and the time processing of the plume (cumulative OH exposure Δt[OH] and the linear decay of primary AVOC and the production/decay of secondary OVOC). As expected, ∆[Ox]/∆[CO] increases with Δt[OH], with significant R2 (0.58 to 0.93). AVOC (aromatics) usually show a decay rate between -0.5 and -3.2 pptAVOC ppbCO-1 per hour, while OVOC either show an increase (secondary production) or a decrease. The production rate is by far the strongest, up to 18 pptOVOC ppbCO-1 per hour (acetaldehyde) during the eastern flight 33 in Paris. Our results set a benchmark for future photochemical studies to compare with. While the anthropogenic origin of some BVOC (terpenoids) and interferences are not excluded, it also emphasizes the importance of the VOC biogenic fraction in anthropogenically influenced environments, which is expected to increase in a warming climate.

Oxidative potential of particulate matter and its association to respiratory health endpoints in high-altitude cities in Bolivia.

Exposure to particulate matter (PM) pollution is a significant health risk, driving the search for innovative metrics that more accurately reflect the potential harm to human health. Among these, oxidative potential (OP) has emerged as a promising health-based metric, yet its application and relevance across different environments remain to be further explored. This study, set in two high-altitude Bolivian cities, aims to identify the most significant sources of PM-induced oxidation in the lungs and assess the utility of OP in assessing PM health impacts. Utilizing two distinct assays, OPDTT and OPDCFH, we measured the OP of PM samples, while also examining the associations between PM mass, OP, and black carbon (BC) concentrations with hospital visits for acute respiratory infections (ARI) and pneumonia over a range of exposure lags (0-2 weeks) using a Poisson regression model adjusted for meteorological conditions. The analysis also leveraged Positive Matrix Factorization (PMF) to link these health outcomes to specific PM sources, building on a prior source apportionment study utilizing the same dataset. Our findings highlight anthropogenic combustion, particularly from traffic and biomass burning, as the primary contributors to OP in these urban sites. Significant correlations were observed between both OPDTT and PM2.5 concentration exposure and ARI hospital visits, alongside a notable association with pneumonia cases and OPDTT levels. Furthermore, PMF analysis demonstrated a clear link between traffic-related pollution and increased hospital admissions for respiratory issues, affirming the health impact of these sources. These results underscore the potential of OPDTT as a valuable metric for assessing the health risks associated with acute PM exposure, showcasing its broader application in environmental health studies.

Local incomplete combustion emissions define the PM2.5 oxidative potential in Northern India.

The oxidative potential (OP) of particulate matter (PM) is a major driver of PM-associated health effects. In India, the emission sources defining PM-OP, and their local/regional nature, are yet to be established. Here, to address this gap we determine the geographical origin, sources of PM, and its OP at five Indo-Gangetic Plain sites inside and outside Delhi. Our findings reveal that although uniformly high PM concentrations are recorded across the entire region, local emission sources and formation processes dominate PM pollution. Specifically, ammonium chloride, and organic aerosols (OA) from traffic exhaust, residential heating, and oxidation of unsaturated vapors from fossil fuels are the dominant PM sources inside Delhi. Ammonium sulfate and nitrate, and secondary OA from biomass burning vapors, are produced outside Delhi. Nevertheless, PM-OP is overwhelmingly driven by OA from incomplete combustion of biomass and fossil fuels, including traffic. These findings suggest that addressing local inefficient combustion processes can effectively mitigate PM health exposure in northern India.

Disentangling fine particles (PM2.5) composition in Hanoi, Vietnam: Emission sources and oxidative potential.

A comprehensive chemical characterization of fine particulate matter (PM2.5) was conducted at an urban site in one of the most densely populated cities of Vietnam, Hanoi. Chemical analysis of a series of 57 daily PM2.5 samples obtained in 2019-2020 included the quantification of a detailed set of chemical tracers as well as the oxidative potential (OP), which estimates the ability of PM to catalyze reactive oxygen species (ROS) generation in vivo as an initial step of health effects due to oxidative stress. The PM2.5 concentrations ranged from 8.3 to 148 µg m-3, with an annual average of 40.2 ± 26.3 µg m-3 (from September 2019 to December 2020). Our results obtained by applying the Positive Matrix Factorization (PMF) source-receptor apportionment model showed the contribution of nine PM2.5 sources. The main anthropogenic sources contributing to the PM mass concentrations were heavy fuel oil (HFO) combustion (25.3 %), biomass burning (20 %), primary traffic (7.6 %) and long-range transport aerosols (10.6 %). The OP activities were evaluated for the first time in an urban site in Vietnam. The average OPv levels obtained in our study were 3.9 ± 2.4 and 4.5 ± 3.2 nmol min-1 m-3 for OPDTT and OPAA, respectively. We assessed the contribution to OPDTT and OPAA of each PM2.5 source by applying multilinear regression models. It shows that the sources associated with human activities (HFO combustion, biomass burning and primary traffic) are the sources driving OP exposure, suggesting that they should be the first sources to be controlled in future mitigation strategies. This study gives for the first time an extensive and long-term chemical characterization of PM2.5, providing also a link between emission sources, ambient concentrations and exposure to air pollution at an urban site in Hanoi, Vietnam.

Evaluating major anthropogenic VOC emission sources in densely populated Vietnamese cities.

Volatile organic compounds (VOCs) play an important role in urban air pollution, both as primary pollutants and through their contribution to the formation of secondary pollutants, such as tropospheric ozone and secondary organic aerosols. In this study, more than 30 VOC species were continuously monitored in the two most populous cities in Vietnam, namely Ho Chi Minh City (HCMC, September-October 2018 and March 2019) and Hanoi (March 2019). In parallel with ambient VOC sampling, grab sampling was used to target the most prevalent regional-specific emission sources and estimate their emission factors (EFs). Emission ratios (ERs) obtained from ambient sampling were compared between Vietnamese cities and other cities across the globe. No significant differences were observed between HCMC and Hanoi, suggesting the presence of similar sources. Moreover, a good global agreement was obtained in the spatial comparison within a factor of 2, with greater ER for aromatics and pentanes obtained in the Vietnamese cities. The detailed analysis of sources included the evaluation of EF from passenger cars, buses, trucks, motorcycles, 3-wheeled motorcycles, waste burning, and coal-burning emissions. Our comparisons between ambient and near-source concentration profiles show that road transport sources are the main contributors to VOC concentrations in Vietnamese cities. VOC emissions were calculated from measured EF and consumption data available in Hanoi and compared with those estimated by a global emission inventory (EDGAR v4.3.2). The total VOC emissions from the road transport sector estimated by the inventory do not agree with those calculated from our observations which showed higher total emissions by a factor of 3. Furthermore, the inventory misrepresented the VOCs speciation, mainly for isoprene, monoterpenes, aromatics, and oxygenated compounds. Accounting for these differences in regional air quality models would lead to improved predictions of their impacts and help to prioritise pollution reduction strategies in the region.

The Latin America Early Career Earth System Scientist Network (LAECESS): addressing present and future challenges of the upcoming generations of scientists in the region.

Early career (EC) Earth system scientists in the Latin America and the Caribbean region (LAC) have been facing several issues, such as limited funding opportunities, substandard scientific facilities, lack of security of tenure, and unrepresented groups equality issues. On top of this, the worsening regional environmental and climatic crises call for the need for this new generation of scientists to help to tackle these crises by increasing public awareness and research. Realizing the need to converge and step up in making a collective action to be a part of the solution, the Latin America Early Career Earth System Scientist Network (LAECESS) was created in 2016. LAECESS's primary goals are to promote regional networking, foster integrated and interdisciplinary science, organize soft skills courses and workshops, and empower Latin American EC researchers. This article is an initial step towards letting the global science community grasp the current situation and hear the early career LAC science community's perspectives. The paper also presents a series of future steps needed for better scientific and social development in the LAC region.

Evaluation of the Sources, Precursors, and Processing of Aerosols at a High-Altitude Tropical Site.

This work presents the results from a set of aerosol- and gas-phase measurements collected during the BIO-MAÏDO field campaign in Réunion between March 8 and April 5, 2019. Several offline and online sampling devices were installed at the Maïdo Observatory (MO), a remote high-altitude site in the Southern Hemisphere, allowing the physical and chemical characterization of atmospheric aerosols and gases. The evaluation of short-lived gas-phase measurements allows us to conclude that air masses sampled during this period contained little or no anthropogenic influence. The dominance of sulfate and organic species in the submicron fraction of the aerosol is similar to that measured at other coastal sites. Carboxylic acids on PM10 showed a significant contribution of oxalic acid, a typical tracer of aqueous processed air masses, increasing at the end of the campaign. This result agrees with the positive matrix factorization analysis of the submicron organic aerosol, where more oxidized organic aerosols (MOOAs) dominated the organic aerosol with an increasing contribution toward the end of the campaign. Using a combination of air mass trajectories (model predictions), it was possible to assess the impact of aqueous phase processing on the formation of secondary organic aerosols (SOAs). Our results show how specific chemical signatures and physical properties of air masses, possibly affected by cloud processing, can be identified at Réunion. These changes in properties are represented by a shift in aerosol size distribution to large diameters and an increased contribution of secondary sulfate and organic aerosols after cloud processing.

Isoprene in urban Atlantic forests: Variability, origin, and implications on the air quality of a subtropical megacity.

Biosphere-atmosphere interactions play a key role in urban chemistry because of biogenic volatile organic compound (BVOC) emissions. Of the BVOC, isoprene is the most emitted compound; however, it also has anthropogenic origins in urban areas. In this study, we aimed to investigate the spatio-temporal variability and atmospheric impacts of biogenic and anthropogenic isoprene in the subtropical megacity of São Paulo (MASP), Brazil. Several measurement campaigns were conducted in three different urban Atlantic forests (Matão, PEFI, and RMG), and an urban background site (IAG); this equated to a total of 268 samples for the 2018-2019 period. For all sampling points, daytime average concentrations of isoprene were two to three times higher during the rainy season (IAG: 1.75 ± 0.93 ppb; Matão: 0.87 ± 0.35 ppb; PEFI: 0.50 ± 0.30 ppb; RMG: 0.37 ± 0.18 ppb), than those observed during the dry season (IAG: 0.46 ± 0.24 ppb; Matão: 0.31 ± 0.17 ppb; PEFI: 0.17 ± 0.11 ppb; RMG: 0.11 ± 0.07 ppb). Average isoprene concentrations were similar to those observed in other places worldwide, with the exception of the Amazon forest. Our results indicate differences in isoprene concentrations between sites, suggesting that environmental conditions such as the urban heat island and vegetation types, may play a role in spatial variability. Estimates of the isoprene fraction indicated that the biogenic fraction (85%) surpassed the anthropogenic fraction during the rainy season. By contrast, the anthropogenic fraction (52%) exceeded the biogenic fraction during dry periods. These fractions have an impact on potentially forming secondary pollutants gaseous (ozone formation potential: 7.19-33.32 µg m-3), and aerosols (secondary organic aerosols formation potential: 0.41-1.88 µg m-3). These results highlight the role of biogenic isoprene and its potential impact on urban air quality in subtropical megacities; this requires further investigation under future climate change scenarios.

One decade of VOCs measurements in São Paulo megacity: Composition, variability, and emission evaluation in a biofuel usage context.

In South America, the observations of atmospheric pollutants are deficient, and few cities have implemented air quality monitoring programs. In addition, Volatile Organic Compounds (VOCs) observations are still missing, and little is known about their contributions to the atmospheric composition and impacts in a large ethanol usage context like Brazil. Here, we present a wide range of VOCs that have been measured for ten years in São Paulo Megacity (SPM) in different campaigns at traffic, urban and background sites. When compared with other cities worldwide, the average VOCs ambient concentrations in SPM were higher by factors of 2 to 10. However, the ambient VOCs distribution among these cities is homogeneous even for ethanol, aldehydes and alkenes species. Emission ratios (ER) were established related to carbon monoxide and acetylene, which did not depict strong seasonal and interannual variability in SPM. When compared with previous studies, ERs showed an enrichment from road-tunnel to background, suggesting the presence of other sources than traffic. A good agreement in ER was found with Los Angeles and Paris; but limited consistencies with Middle East and Asia cities. Our ethanol measurements show that contrasted ER can be obtained depending on the emission process involved, with a strong impact of evaporation on ethanol concentrations. The multiyear acetaldehyde analysis displayed that ER could be a valuable metric to assess the long-term changes in emissions sources. Finally, VOCs emissions were calculated from ER and compared with those estimated by the global emission inventory (Edgar). The total VOC emissions estimated by the global inventory agree very well with those from our observations up to 75%. Nevertheless, the VOCs speciation is misrepresented in the inventory, mainly for oxygenated and heavier alkanes compounds. These inconsistencies will also have an impact on the quantification of secondary atmospheric pollutants formation associated to road transport emissions.

Disentangling vehicular emission impact on urban air pollution using ethanol as a tracer.

The Sao Paulo Metropolitan Area is a unique case worldwide due to the extensive use of biofuel, particularly ethanol, by its large fleet of nearly 8 million cars. Based on source apportionment analysis of Organic Aerosols in downtown Sao Paulo, and using ethanol as tracer of passenger vehicles, we have identified primary emissions from light-duty-vehicles (LDV) and heavy-duty-vehicles (HDV), as well as secondary process component. Each of those factors mirror a relevant primary source or secondary process in this densely occupied area. Using those factors as predictors in a multiple linear regression analysis of a wide range of pollutants, we have quantified the role of primary LDV or HDV emissions, as well as atmospheric secondary processes, on air quality degradation. Results show a significant contribution of HDV emissions, despite contributing only about 5% of vehicles number in the region. The latter is responsible, for example, of 40% and 47% of benzene and black carbon atmospheric concentration, respectively. This work describes an innovative use of biofuel as a tracer of passenger vehicle emissions, allowing to better understand the role of vehicular sources on air quality degradation in one of most populated megacities worldwide.