Environmental science: atmospheres最新文献

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While photochemical aging is known to alter secondary organic aerosol (SOA) properties, this process remains poorly constrained for anthropogenic SOA. This study investigates the photodegradation of SOA produced from the hydroxyl radical-initiated oxidation of naphthalene under low- and high-NO _x conditions. We used state-of-the-art mass spectrometry (MS) techniques, including extractive electrospray ionization and chemical ionization MS, for the in-depth molecular characterization of gas and particulate phases. SOA were exposed to simulated irradiation at different stages, i.e., during formation and growth. We found a rapid (i.e. >30 min) photodegradation of high-molecular-weight compounds in the particle-phase. Notably, species with 20 carbon atoms (C₂₀) decreased by 2/3 in the low-NO _x experiment which was associated with particle mass loss (∼12%). Concurrently, the formation of oligomers with shorter carbon skeletons in the particle-phase was identified along with the release of volatile products such as formic acid and formaldehyde in the gas-phase. These reactions are linked to photolabile functional groups within the naphthalene-derived SOA products, which increases their likelihood of being degraded under UV light. Overall, photodegradation caused a notable change in the molecular composition altering the physical properties (e.g., volatility) of naphthalene-derived SOA.

The impact of cooking with solid fuels on neighborhood-scale PM_2.5 concentrations in rural towns and communities is poorly quantified due to the lack of credible ground-level monitoring sites and spatial heterogeneity at a scale that is below the resolution of remote sensing GEOS-Chem hybrid models. Emissions of PM_2.5 from use of open fires for cooking in rural Mexico are known to cause poor indoor air quality. The effectiveness of different intervention strategies to reduce such pollution exposures also varies because of different local building densities and source intensities. In this study, the effectiveness of stove intervention strategies on the neighborhood-scale PM_2.5 concentrations were evaluated in a village Cucuchucho, located in the Purepecha highlands of Mexico. The Quick Urban & Industrial Complex (QUIC) is deployed in the assessment. The model's performance in simulating interactions between pollutants and flow around building structures is validated through comparison with a water channel experiment, which shows good quantitative agreement. The case study simulation results demonstrate that upstream households contributed ∼30% of concentrations, and current trends will not meet WHO air quality guidelines or interim targets. The magnitude of neighborhood-scale PM_2.5 concentrations depends on the intervention and community structure. Based on these simulations, a statistical model is presented to estimate ambient neighborhood PM_2.5 pollution concentrations for more communities at a regional level. The statistical model allows neighborhood PM_2.5 pollution to be included in estimates of health burdens from household pollution in Mexico using readily accessible community parameters.

The role of biogenic emissions in forming ozone (O₃) and secondary organic aerosol (SOA) is increasingly important with decreasing anthropogenic emissions in China. However, biogenic volatile organic compounds (BVOCs) from urban green spaces are often neglected mainly because available land cover datasets do not reflect the distribution and density of vegetation in urban areas. In this study, urban BVOC emissions in Beijing at 1 km spatial resolution are estimated based on Google Earth Engine and a high-resolution land cover dataset and then used for air quality simulation in the summer of 2017. The updated urban BVOC emissions show better agreement with observed isoprene emission fluxes than other inventories. Air quality simulation shows that the contribution of urban BVOCs to the maximum daily averaged 8 h O₃ in Beijing typically exceeds 5 ppb with the maximum value of 8 ppb. Although BVOC emissions are higher in rural areas than urban areas, their contributions to O₃ concentrations are lower in rural regions. In contrast, the mean concentrations of biogenic SOA (BSOA) in urban areas (1.44 μg m⁻³) are 17% lower than in rural areas. Compared to other inventories, the average difference in BSOA concentrations in urban areas reached 0.18 μg m⁻³, and the relative changes in ISOA, MSOA, and SSOA were 14.3%, 17.7%, and 32.6%, respectively. This study emphasizes the importance of considering BVOC emissions from urban green spaces in understanding urban atmospheric chemistry. The methodology used to update urban green spaces in this study is equally applicable to other cities.

There is no standard sampling and analysis method for vapor phase per- and polyfluoroalkyl substances (PFAS) that can be routinely applied to soil gas, sewer/conduit gas, and indoor air samples. We have validated a thermal desorption GC/MS/MS method for the measurement of a set of fluorotelomer alcohols and perfluorooctanesulfonamides collected on multi-bed sorbent tubes. Applications to perfluorocarboxylic acids were also evaluated since there is debate regarding under what circumstances these compounds could be observed moving into gas phase. Perfluorooctanoic acid (PFOA) met Method TO-17 calibration requirements when calibrated using National Institute of Standards and Technology (NIST) traceable standard solutions introduced through the thermal desorption system and using multiple reaction monitoring (MRM) transitions based on precursor mass ions identified in the PFOA spectra. However, subsequent detailed studies suggested that PFOA was decomposing during the thermal desorption sample introduction step when comparing two alternative GC/MS sample introduction techniques. The primary peak resulting from the thermal desorption of PFOA standard had spectra consistent with perfluoro-1-heptene (PFHp-1), suggesting that a degradation reaction was occurring. Therefore, the identification of the PFCA compounds in this method is currently subject to a potential positive interference from the corresponding perfluoroalkene and other thermally labile PFAS. Thus, it may be beneficial to limit the application of the thermal desorption GC/MS/MS method to the fluorotelomer alcohols and perfluorooctanesulfonamides and use a parallel solvent extraction approach to quantify the PFCA-related compounds. Method validation including desorption efficiency, second source verification, storage stability and method detection limit tests were successfully completed for the fluorotelomer alcohols and perfluorooctanesulfonamides target analytes.

This study investigates aerosol and wet deposition chemistry at Acadia National Park (Maine, U.S.) using data between 1 January 2001 and 31 December 2021. Results show that PM_2.5 is highest in summer and dominated by sulfate salts and organics (less contribution from elemental carbon), whereas nitrate salts and sea salt were highest in winter. Fine soil is most pronounced from March through August due most likely to long-range transport. Residual mass (PM_2.5 – reconstructed PM_2.5) was negative from November–March, with reasons discussed for its seasonal changes. Major regional sources of pollution are upwind from populated cities generally to the southwest of Acadia. Extreme PM_2.5 events are mostly driven by regional pollution events with others due to transported summertime biomass burning plumes that increased in frequency in the most recent years. Aerosol composition on cold air outbreak days showed that ammonium sulfate and organics dominated PM_2.5, which provides useful information for studies focused on understanding the formation and evolution of offshore cloud decks during the winter. Monthly mean pH in wet deposition ranges from 4.8 to 5.1 with the lowest values in July when contributions from acidic ions are highest (sulfate, nitrate). Average annual pH increased from 4.64 to 5.23 over the study period coincident with reductions in sulfate and nitrate levels. Sea salt constituents dominated the wet deposition aqueous ion concentrations from November to March, whereas in the other months sulfate and nitrate were highest. Interrelationships between aerosol and wet deposition species relevant to secondarily produced species, dust, and sea salt provide support for aerosol–precipitation interactions that warrant a further look with more robust methods.

This study investigates the impact of forest fires on air quality in India's northeastern (NE) region, focusing on Guwahati, Tezpur, and Aizawl. The North-Eastern Forest cluster, contributing 36% to the total forest cover, emerges as a hotspot with the highest number of fire detections (40%). Population growth and shifting cultivation practices have intensified the frequency of fires. The study spans 2013–2016, assessing PM₁₀, PM_2.5, ozone (O₃), carbon monoxide (CO) and nitrogen oxide (NO_x) concentrations in the three NE cities. Guwahati consistently recorded PM₁₀ concentrations above National Ambient Air Quality Standards (NAAQS), indicating persistent air quality challenges. Tezpur and Aizawl maintained concentrations below NAAQS, with Aizawl displaying Good to Satisfactory air quality on a significant portion of observed days. During forest fire (FF) events from 2013 to 2016, PM₁₀, PM_2.5, O₃, CO, and NO_x concentrations rose, suggesting a direct correlation between FF and deteriorating air quality, especially when FF counts were above 100. During these events, a shift in air quality levels was observed, affecting most parameters in Aizawl and varying for other cities. Diurnal patterns during FF events indicated increased pollutant levels. The most prominent change was observed in PM₁₀ in all stations. Backward air–mass trajectory analysis confirms the influence of NE-India as a significant pollution source during FF. This study underscores the urgent need for targeted interventions to mitigate the impact of FF on air quality in the NE region, emphasising the intricate relationship between ecological practices, forest fires and atmospheric conditions.

Health-related impacts e.g. respiratory and cardiovascular morbidity and mortality, associated with exposure to atmospheric particulate matter (PM) are globally considered important and are not completely understood. Oxidative potential (OP), defined as a measure of the capacity of PM to oxidise target molecules, has been previously proposed as an alternative relevant biological metric in health studies to better quantify toxicological responses associated with PM exposure than aerosol mass alone. Several methods are currently used to assess the oxidative capacity of PM. In this study, the dithiothreitol (DTT) assay was used, which is the most commonly used technique to estimate OP. This assessment is easy-to-operate, low-cost, effective and reproducible. The first step was to modify the DTT methodology based on previous applications, which entailed choosing an appropriate extraction procedure and -setup. The redox activity of size-resolved PM samples collected in three low-income urban settlements in South Africa, i.e. Jouberton, KwaZamokuhle and Zamdela was evaluated and related to their chemical composition through correlation analysis. Furthermore, it was attempted to determine seasonal variations of DTT redox activity through normalisation according to PM mass (DTTm) and sampled volume (DTTv) for outdoor and indoor environments. The results indicated higher redox activity for the finest (<1 μm) particles compared to the coarser particulates (1–10 μm) for both outdoor and indoor environments. DTT redox activity of PM, especially, in the PM_1–10 particle size fraction, had strong correlations with elemental (EC) and organic carbon (OC), as well as trace elements and water-soluble inorganic species for outdoor and indoor samples. Possible atmospheric aerosol emission sources suggested from these correlations include primary emissions from domestic- and open biomass burning, vehicles and industrial activities, as well as secondary particle formation (e.g. sulphate).

Delhi is one of the most polluted regions in the world, yet studies focusing simultaneously on atmospheric aerosol particle size distribution (PSD) and chemical composition, as well as their inter-relationship, are still lacking. Additionally, the high condensation sink (CS) in Delhi has drawn less attention to new particle formation (NPF) and the role of chemical composition. This study explored the intricate interplay among particle size distribution, meteorology, and chemical composition within the atmospheric environment of Delhi. Our findings reveal pronounced seasonal variations in the particle number and mass concentration levels following variations in atmospheric conditions and emission sources across different seasons. Furthermore, we identified condensation sink as a primary factor governing the NPF, with no NPF event observed when daytime CS was above 0.06 s⁻¹. While precursors such as H₂SO₄ and NH₃ were abundant, they did not appear to be limiting factors for NPF. However, due to the lack of direct measurements of sub-10 nm particles and precursor gases such as H₂SO₄, amines, and organic vapours, the conclusions regarding the role of chemical precursors remain speculative. Furthermore, on days with comparable condensation sinks, the chemical composition exhibits no significant variation between NPF and non-NPF days, with organics contributing to about 50% of the PM_2.5, emphasizing the dominance of physical processes. Our observations highlight the critical influence of relative humidity on particle formation, with higher atmospheric liquid water content inhibiting NPF. Additionally, we investigated the simultaneous time variations in PSD and mass composition of PM_2.5, revealing significant mass composition variations during the first (daytime) and second (night-time) growth. Notably, during the daytime growth of nucleated particles, increases in sulphate and low volatile oxygenated organics suggest the involvement of sulphuric acid and oxidized vapours in early particle growth. However, the unclear relationship between the growth rate and chemical composition reveals the complexity of new particle formation in polluted environments such as Delhi. While PM_2.5 composition offers insights into growth processes, its relevance to nucleation-mode particles is limited. Thus, this study further emphasizes the need for sub-10 nm PSD and precursor gaseous measurements to seek a better understanding of NPF in a high CS environment in the Global South.

Cleaning detergents are a source of numerous volatile organic compounds (VOCs) which are highly reactive towards ozone leading to the formation of secondary organic aerosols (SOA) in indoor environments. Here we perform real-time measurements of the organic composition of aerosols produced upon ozone reaction with floor cleaning detergent by extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) coupled to a chamber reactor. The experiments were performed in the absence of light and under light irradiation (320 nm < λ < 400 nm) simulating the fraction of sunlight that penetrates indoors. The multiple increases in particle number concentrations correspond to rise in the signal intensity of specific species. Notably, the secondary increase in particle mass concentration is mainly contributed by highly oxidized molecules (HOMs), which increased from 16.5% upon ozone oxidation to 19.9% under photo-oxidation reactions. A large fraction of CHON compounds such as imidazole, pyrazine/pyrimidine, and azaindole was observed most likely formed through the reaction of O₃ with benzothiazole (constituent of the cleaning detergent). The difference between the molecular compositions detected in the absence of light and in the presence of light indicates that sunlight penetrating through the windows can affect the SOA produced by the reaction of ozone with the floor cleaning detergent.