Environmental science: atmospheres最新文献

This study explores the potential contribution of secondary production of OH radicals in aerosols and cloud/fog conditions arising from brown carbon (BrC) triplet state chemistry. For this purpose, extracts of brown carbon from atmospheric aerosols from Grenoble, France, were analyzed for their ability to produce triplet states from the degradation of a common triplet state probe, 2,4,6-trimethylphenol (TMP). This ability of brown carbon to produce triplet states was compared to that of three photosensitizers, where it was found that vanillin (VL) showed a similar rate of degradation of the probe and was hence chosen as an alternative to BrC in aqueous aerosols to investigate OH formation from triplet states. The rates of OH formation from the triplet states were compared to those from nitrate anions (NO₃⁻) and hydrogen peroxide (H₂O₂), which are well-known sources of OH radicals in the aqueous phase, and a species that is structurally similar to VL, 4-hydroxybenzaldehyde (4HB). VL and 4HB both showed a 1–2 orders of magnitude higher rate of secondary OH formation than NO₃⁻, while it was similar or one order of magnitude smaller than H₂O₂. To evaluate the influence of the different OH radical sources in aqueous aerosols and cloud/fog conditions, the concentrations of the species were summarized from the literature. Considering the concentrations of HULISs in aerosols, the rates of secondary OH formation from BrC triplet states could potentially represent a significant source of OH in the atmospheric aqueous phase under some circumstances. This study shows the relevance of further investigations into the role of triplet states in impacting atmospheric oxidative capacity and studying other effects of triplet states in aerosols, a field that is, until now, still not fully understood.

Though the importance of bioaerosols is increasing with the changing climate, very little is known about the chemistry of bioaerosols, their atmospheric fate, and chemical composition. This paper is focused on the characterization of chemical functional groups of four atmospherically relevant bioaerosols: pollen (lodgepole pine and rabbitbrush), fungi (western gall rust), bacteria (Pedobacter and hay bacillus), and algae (spirulina). For this purpose, the proton nuclear magnetic resonance (¹H-NMR) technique was used on water-soluble extracts of the selected bioaerosols, while quantitative analysis of individual organic species (saccharides, amino acids, and fatty acids) was performed using gas chromatography mass spectrometry (GC-MS), ultra-high performance liquid chromatography (UPLC-MS), and UV-Vis-NIR (ultraviolet-visible-infrared) spectrophotometry. The obtained ¹H-NMR results revealed major contributions from aliphatic protons in Bacillus (50.2%) and Pedobacter (57.0%) bacteria, western gall rust fungus (39.7%), spirulina algae (73.8%), and rabbitbrush pollen (31.3%). Protons from saccharides were dominant in lodgepole pine pollen (27.6%). The quantitative analysis shows that the saccharide glucose is common among the analyzed bioaerosols, as well as proline, leucine, isoleucine, alanine, and phenylalanine amino acids, and palmitic, oleic, linoleic, linolenic, and stearic fatty acids (except in Bacillus bacteria). Concentrations of analyzed saccharides ranged between 2.01 μg mg⁻¹ of dry mass (in Bacillus bacteria) and 183.54 μg mg⁻¹ (in lodgepole pine pollen), followed by amino acids (from 2.57 μg mg⁻¹ in western gall rust fungus to 21.38 μg mg⁻¹ in Bacillus bacteria), and fatty acids (from 0.05 μg mg⁻¹ in Bacillus bacteria to 25.82 μg mg⁻¹ in lodgepole pine pollen). Comparison of ¹H-NMR and quantitative analyses showed a good correlation (R² = 0.608) between the saccharide segment of ¹H-NMR bioaerosol spectra and individual saccharide analysis.

Herein, we examine the generation of nanoparticles from tire and road interactions, with a focus on two key aspects: replicating real-world conditions in a controlled environment for particle generation and analysing the collected particles through both online and offline techniques. In order to generate realistic wear patterns, third body particles were used in a standardized laboratory tire testing facility across dynamic and static speeds and load profiles. The findings indicated that milled stone dust as a third body particle significantly disrupted the nanoparticle size range, complicating the differentiation between tire-based and third-body-based nanoparticles. However, using sand as a third body particle, the interference showed comparatively lower background noise within the nanoparticle region. Here, steady-state cycles were employed to discern the relationships between force events and nanoparticle generation, which were compared to analyses conducted over an entire dynamic drive cycle. The steady-state cycles revealed that high lateral forces (>2 kN) yielded the highest nanoparticle concentrations, surpassing background levels by over two orders of magnitude. Meanwhile, the drive cycle trials indicated that approximately 70% of the emitted nanoparticles throughout the entire drive cycle were semi-volatile emissions, likely originating from vaporization events. ICP-MS results confirmed the presence of tire-related elements in the nanoparticle region, but definitive attribution to the tire or road surface remains a challenge for the field. This study underscores the complexities inherent in generating, collecting, and assessing submicron tire wear particles, laying the groundwork for addressing uncertainties and refining non-exhaust tire emission methodologies.

Particulate matter (PM) emitted from unpaved rural roads presents a potential inhalation hazard to people living and working near them. In the absence of site-specific exposure data, plume dispersion modeling can be used to predict ambient particulate concentrations in the vicinity of the unpaved roads. Hourly averaged PM₁₀ concentrations were measured near a gravel road using an EPA reference method resulting in a geometric mean of 50 μg m⁻³. With these ambient concentrations, the AERMOD plume dispersion model was used to derive a PM emission factor of 444 g/VKT (grams per vehicle kilometer travelled). This result was lower than the emission factor calculated using the EPA's AP-42 guidance for unpaved roads (795 g/VKT). The transient nature of the plume of PM concentrations due to road traffic was also evaluated using a direct-reading instrument. Vehicle speed and wind speed were found to be significant determinants of PM concentration, average PM concentration, and total PM mass for each plume. Each vehicle produced an average concentration of 4096 μg m⁻³ over the duration of the plume. Therefore, residents near the road are potentially exposed to substantially higher short-term concentrations from individual plumes than would be indicated by hourly averages.

Furans are emitted from biomass burning (BB) and contribute to the reactivity of BB plumes with a significant proportion. Consequently, the development of comprehensive furan oxidation schemes is one of the crucial elements towards a better understanding of BB plume chemistry. Nighttime oxidation is supposedly dominated by NO₃ radicals and O₃. The present study has chosen 2,5-dimethylfuran (25DMF) as a model compound for the development of an O₃ oxidation mechanism for furans. Experiments were performed in the QUAREC atmospheric simulation chamber (QUAREC ASC) at 299 ± 2 K and a pressure of 980 ± 20 mbar under dry conditions (relative humidity < 0.1%) targeting the reaction kinetics, the OH formation and the oxidation mechanism. The reactions were monitored by long-path FTIR spectroscopy and a PTR-ToF-MS instrument. We determined a rate coefficient of (3.3 ± 1.0) × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹ for the target reaction using the relative-rate method. An OH yield of 25 ± 10% was obtained when using 1,3,5-trimethylbenzene as an OH tracer. Reaction products are formaldehyde, methyl glyoxal, ketene, glyoxal, methyl hydroperoxide, acetic anhydride, and acetic acid, respectively. The methyl glyoxal, glyoxal and formaldehyde yields were found to be sensitive to the overall peroxy radical level in the system. The PTR-MS data indicate further reaction products, which are tentatively assigned. A mechanism is postulated to account for the clearly identified reaction products. Overall, the obtained results indicate that O₃ oxidation of furans might contribute to acidity in nighttime BB plumes.

Air pollution disproportionately affects African countries, including Uganda, but it is inadequately studied in these settings. The emergence of low-cost sensors offers an opportunity to improve routine air quality monitoring, assess interventions, and track progress. This study aimed to assess the spatiotemporal trends of PM_2.5 in Kampala and Jinja cities in Uganda, whilst exploring the influence of meteorological parameters on PM_2.5. Calibrated PM_2.5 values and meteorological parameters for three years (2020 to 2022) were obtained from 58 local low-cost sensors and 6 weather stations. Hourly averages for PM_2.5 and meteorological data underwent necessary pre-processing, and various statistical analyses, including descriptive statistics, time series trends, spatial variation, Spearman rank correlation, and multivariate regression, were performed. The multivariate linear regression with a gamma-link function was selected as the model with the best fit. The average annual PM_2.5 levels in Kampala and Jinja were 41.1 μg m⁻³ (±18.91 μg m⁻³) and 25.6 μg m⁻³ (±15.5 μg m⁻³), respectively, significantly exceeding the recommended World Health Organisation annual guideline values of 5 μg m⁻³. Meteorological parameters exhibited varying degrees of relationships with PM_2.5 in both cities; multivariate regression indicated that meteorological factors could explain about 18% of the variation of PM_2.5 in Kampala and 7% in Jinja. Both cities experienced a decrease in PM_2.5 levels during the COVID-19 pandemic lockdown with Kampala experiencing a 31% reduction (average decrease of 11.2 μg m⁻³) and Jinja a 17% reduction (average decrease of 3.8 μg m⁻³). This study provides insights into the air quality challenges faced by a rapidly urbanising city in sub-Saharan Africa, the promise of locally made low-cost sensors, and how meteorology influences local air pollution and lays the foundation for informed decision-making to safeguard public health and promote a sustainable environment. The findings highlight the urgent need for targeted interventions and policy initiatives to address air pollution in Uganda.

Organic aerosols (OA) constitute an important fraction of fine particulate matter (PM_2.5) air pollution, yet accurate and efficient OA modeling within chemical transport models (CTM) remains a challenge. Volatility basis set (VBS) schemes for OA have demonstrated improved performance in simulating OA, particularly for primary organic aerosol (POA), but their computational complexity impedes application to advanced modeling tasks, such as detailed source apportionment. Conversely, simpler “two-product” schemes are efficient and compatible with source apportionment techniques but many of them tend to overestimate POA by treating it as non-volatile. Either VBS or 2-product schemes can perform well for secondary organic aerosol (SOA) depending upon the data and assumptions used to model SOA formation from precursors. In this study, we update the Comprehensive Air Quality Model with extensions (CAMx) “SOAP” 2-product modeling framework by (1) treating POA as semivolatile using an efficient scheme, (2) adding SOA formation from semivolatile organic compounds (SVOCs), and (3) adopting SOA yields derived from the widely-used Community Multiscale Air Quality (CMAQ) AERO7 scheme. The first update allows temperature-dependent partial evaporation of POA to SVOC, which is subsequently oxidized in the gas phase. For the latter two updates, SOA yields are updated to emulate the AERO7 scheme based on an offline conceptual model. We implemented these changes within the existing SOAP2 scheme of CAMx to create a new scheme called “SOAP3”. A series of CTM simulations were conducted with the SOAP3 scheme to simulate OA and its components in China during July and November 2018. Results were validated against surface observations and compared to the SOAP2 and AERO7 schemes. Compared to SOAP2, SOAP3 substantially reduced POA proportions (by 10–24%) and increased SOA concentrations (by 45–193%) for selected regions. SOAP3 performs more like the AERO7 scheme than SOAP2 in terms of the simulated OA components and improved accuracy compared to observations. Uncertainties and limitations of the current SOAP3 scheme are also discussed. Our study demonstrates a feasible and readily implemented methodology for improving two-product OA modeling, which is currently employed in many CTMs.

Harmful algal blooms (HABs) are projected to become increasingly prevalent, extending over longer periods and wider geographic regions due to the warming surface ocean water and other environmental factors, including but not limited to nutrient concentrations and runoff for marine and freshwater environments. Incidents of respiratory distress linked to the inhalation of marine aerosols containing HAB toxins have been documented, though the risk is typically associated with the original toxins. However, aerosolized toxins in micrometer and submicrometer particles are vulnerable to atmospheric processing. This processing can potentially degrade HAB toxins and produce byproducts with varying potencies compared to the parent toxins. The inhalation of aerosolized HAB toxins, especially in conjunction with co-morbid factors such as exposure to air pollutants from increased commercial activities in ports, may represent a significant exposure pathway for a considerable portion of the global population. Understanding the chemistry behind the transformation of these toxins can enhance public protection by improving the existing HAB alert systems.

An unmanned aerial vehicle was deployed daily in Riverside, CA from August to November 2020, capturing vertical ozone and particulate matter measurements. Flights took place in the early morning and late afternoon, resulting in 321 vertical profiles from the surface to 500 m above ground level. The measured ozone mixing ratio is statistically compared with ground-based measurements at the Riverside–Rubidoux regulatory air monitoring site in Jurupa Valley, CA and with CMAQ simulated concentrations to assess consistency with the nearest reference monitor and model skill at reproducing the observed vertical structure, respectively. The default model configuration overestimates ground-level ozone by 17.7 ppb in the morning and underestimates it by an average of 2.9 ppb in the afternoon. The sensitivity of the model to factors such as planetary boundary layer (PBL), eddy diffusivity, NO_x emissions, and VOC emissions is investigated by modifying key physics and emissions settings in a series of simulations. We found that our default PBL scheme used in the default CMAQ simulation negatively biases the PBL height in the nighttime and positively biases it in the daytime compared to the observations retrieved from a ceilometer. For the observational region of interest, NO_x emissions are concluded to be largely underestimated, leading to biases in modeled ozone concentration. We conclude with recommendations for achieving model parity with localized measurements.

Due to rapid urbanization and lifestyle changes, people in developing countries like India spend most of their time indoors, just like those in developed countries. Indoor air pollution (IAP) studies in urban built environments in India are yet to gain momentum. Studies conducted so far are restricted to reporting pollutant concentration, providing limited insights into pollutants' source, transport, and fate. Comprehensive studies are critical to assessing IAP severity and developing and deploying effective mitigation strategies in built environments. The present study includes spatio-temporal monitoring of particulate matter (PM) in a multizonal residential apartment using a network of low-cost air quality monitors and research-grade instruments to characterize emission sources, assess transport metrics, estimate spatial exposure, calculate I/O ratios, and assess efficacies of different mitigation measures. Sub-micron particles dominated number size distribution for cooking and incense. Operation of air conditioners (AC) led to faster transport of pollutants from the kitchen to the bedrooms. PM exposure in all zones relative to the kitchen had comparable (∼0.8–0.9) exposure during cooking. The average I/O ratios during cooking were elevated throughout the apartment, with the kitchen (10.1 ± 8.9) and bedrooms (7.2 ± 5.7 & 7.4 ± 5.9) being the highest and lowest, respectively. Natural ventilation through balcony doors led to an average exposure reduction of 74–86% in different zones. AC operation reduced cumulative exposure, which was further reduced upon affixing a filter sheet on the AC pre-filter. Among the mitigation measures assessed, the highest cumulative loss rate (2.3 ± 0.1 h⁻¹) was observed for the portable air cleaner with the default HEPA filter.