Environmental science: atmospheres最新文献

Highly oxygenated organic molecules (HOMs) are significant contributors to the formation of secondary organic aerosols (SOAs) and new particles in the atmosphere. The process of HOM formation via autoxidation is highly dependent on several factors, such as temperature, relative humidity (RH), and initial ozone concentration, among others. The current work investigates how temperature and RH affect the formation of HOMs in SOAs from limonene ozonolysis. Experiments were conducted in a laminar flow tube reactor under different experimental conditions (T = 5 °C and 25 °C; RH = 15% and 75%). A scanning mobility particle sizer was used to measure the concentration and size distribution of generated SOA particles. Fourier transform ion cyclotron resonance mass spectrometry was used to detect and characterize HOMs and SOAs. Experimental results show that lower temperatures (i.e., T = 5 °C) and higher RH levels (e.g., RH = 75%) promote the generation of HOMs and SOAs. Limonene-oxidation-derived HOMs exhibit a preference for stabilization under low-temperature and high-RH conditions. Within this context, semi-volatile, low-volatile, and extremely low-volatile organic compounds play a significant role. Our experimental findings indicate that the formation of C₁₀ compounds during limonene ozonolysis is strongly influenced by peroxy radical chemistry. Given that peroxy radicals are key intermediates in this process, their reactions—including autoxidation and bimolecular termination pathways—likely play a significant role in the formation and stabilization of HOMs in SOAs. The observed product distributions also suggest that these radicals contribute to the incorporation of multiple oxygen atoms, facilitating the formation of ELVOCs and LVOCs that ultimately drive particle-phase growth. The present work can improve our understanding of the generation of biogenic HOMs and SOAs at different temperatures and RH, which can be used in future exposure risk or climate models to provide more accurate air quality prediction and management.

Recently Pérez-Peña et al. published a paper in this journal on the potential atmospheric fate of trifluoroacetaldehyde (CF₃CHO) as a source of CF₃H (HFC-23). In their work they utilized both a box model and a global chemistry and transport model to evaluate the production of CF₃H from the photolysis of CF₃CHO, the latter generated from photochemical oxidation of HFO-1234ze (CF₃CHCHF). Certain chemical assumptions and simplifications were made. We believe the assumptions utilized by Pérez-Peña et al. misrepresent the environmental fate of CF₃CHO. In the following, we present our comments on both the photolysis and the wet and dry deposition of CF₃CHO. Furthermore, we contemplate the impact of the potential deposition of CF₃CHO on the formation of trifluoroacetic acid (CF₃COOH) during the environmental processing of CF₃CHO.

In Pérez-Peña et al. (DOI: https://doi.org/10.1039/d3ea00120b), we used a suite of box model simulations to determine how trifluoroacetaldehyde (CF₃CHO) produced from HFO-1234ze is lost in the atmosphere and how much fluoroform (CHF₃ or HFC-23) could potentially be produced as a result. For the first time in any modelling study, our simulations included both a minor CF₃CHO photolytic loss channel leading to CHF₃ production and physical removal of CF₃CHO via wet and dry deposition. In their comment, Sulbaek Andersen, Nielsen, and Franklin query the assumptions used to simulate these processes. Here, we show that the importance of the photolytic loss pathway remains a matter of community debate and that our results are relatively insensitive to assumptions underlying simulation of deposition. We reiterate the need for measurements of CF₃CHO physical properties to reduce the uncertainties in these processes and pave the way for more sophisticated models.

Wildfires are a major source of aerosols during summer in the western United States. Aerosols emitted from wildfires could significantly affect air quality, human health, and the global climate. This study conducted a comparison of aerosol characteristics during wildfire smoke-influenced and non-smoke-influenced days. Ambient particle size distribution (PSD) data were collected in Reno, Nevada, between July 2017 and October 2020. During this period, the site was impacted by smoke from over a hundred wildfires burning in a wide range of ecosystems in the western United States located at different distances from the measurement site. The smoke-influenced days were identified using satellite images, a hazard mapping system, and wind back-trajectory. Positive matrix factorization (PMF) was applied to identify the main sources and their characteristics. The wildfire aerosols were observed to have a number mode diameter of 212 nm, which is significantly larger than aerosols on non-smoke-influenced days (61 nm). In addition to the increase in particle size, wildfires made a large contribution to PM_2.5 and CO concentrations. During fire-prone months (July, August, and September) from 2016 to 2021, 56% to 65% of PM_2.5 and 18% to 26% of CO concentrations could be attributed to wildfire emissions in the study area. On an annual basis, wildfire emissions were responsible for 35% to 47% of PM_2.5 concentrations and 5% to 12% of CO concentrations.

Ambient air pollution has been linked to several health endpoints. The WHO attributes 7 million deaths annually to air pollution with particulate matter (PM_2.5) being the pollutant of critical importance due to its devastating health effects. Air quality monitoring is very limited in sub-Saharan African (SSA) countries and although satellite remote sensing has helped to bridge the huge air quality data gaps, these measurements have not been validated against ground-level measurements in these countries. We therefore evaluated the efficiency of low-cost sensors in estimating PM_2.5 concentrations in an African city through comparison of low-cost sensor data with satellite aerosol optical depth (AOD) data leveraging complex machine learning (ML) methods. Low-cost sensor data were collected from a monitoring network in Accra, Ghana, with AOD measurements extracted from the MODIS MCD19A2v061 dataset and processed using the MAIAC algorithm. Ordinary Least Squares regression, Random Forest, Extra Trees, Boosted Decision Trees and XGBoost were used to establish the relationship between AOD and low-cost sensor PM_2.5 measurements incorporating meteorological data. We observed significant positive relationships for two low-cost sensors deployed in the network (Clarity Node S and Airnote). The R² values were, however, low, ranging from 0.18 to 0.27, with the corrected Airnote data recording the highest R². The ML models which integrated temperature and humidity improved the R² values with the Boosted Decision Tree demonstrating the best predictive capability. Seasonal variability was found to have a strong influence on model performances with the dry season model performing significantly better than the wet season model. Consistent with other studies, AOD explained only a small proportion of ground-level PM_2.5 variations. Evidence from this sensor network in Accra suggests that AOD predicts ground-level PM_2.5 measured with low-cost sensors in a manner similar to conventional air monitoring instrumentation. However, for low-cost sensors to be deemed a good substitute for satellite AOD, data correction with complex algorithms developed in the same research location will be required.

Incorporating the reactions of fifty peroxy radicals (RO₂) with the hydroxyl radical (OH) into the global chemistry transport model, STOCHEM-CRI, affected the composition of the troposphere by changing the global burdens of NO_x (−2.7 Gg, −0.5%), O₃ (−2.3 Tg, −0.7%), CO (−3.2 Tg, −0.8%), HO_x (+2.1 Gg, +7.7%), H₂O₂ (+0.5 Tg, +18.3%), RO₂ (−8.0 Gg, −18.2%), RONO₂ (−19.4 Gg, −4.7%), PAN (−0.1 Tg, −3.4%) HNO₃ (−7.4 Gg, −1.3%) and ROOH (−96.9 Gg, −3.8%). The RO₂ + OH addition reactions have a significant impact on HO₂ mixing ratios in tropical regions with up to a 25% increase, resulting in increasing H₂O₂ mixing ratios by up to 50% over oceans. Globally, a significant amount of organic hydrotrioxides (ROOOH) (86.1 Tg per year) are produced from these reactions with CH₃OOOH (67.5 Tg per year, 78%), isoprene-derived ROOOH (5.5 Tg per year, 6%) and monoterpene-derived ROOOH (4.2 Tg per year, 5%) being the most significant contributors. The tropospheric global burden of CH₃OOOH is found to be 0.48 Gg. The highest mixing ratios of ROOOH, of up to 0.35 ppt, are found primarily in the oceans near the tropical land areas. The RO₂ + OH reactions have a small, but noticeable, contribution to OH reactivity (∼5%) over tropical oceans. Additionally, these reactions have a significant impact on RO₂ reactivity over tropical oceans where losses of the CH₃O₂ radical, isoprene derived peroxy radical (ISOPO₂) and monoterpene derived peroxy radical (MONOTERPO₂) by OH can contribute up to 25%, 15% and 50% to the total RO₂ loss, respectively. The changes in RO₂ reactivity influence the global abundances of organic alcohols (ROH) which are important species due to their crucial impact on air quality. The ROOOH generate secondary organic aerosol (SOA) of up to 0.05 μg m⁻³ which affects the Earth's radiation budget because of enhancing modelled organic aerosol by up to 5% and 2000% on land surfaces and the remote tropical oceans, respectively.

Kampala, the political and economic capital of Uganda and one of the fastest urbanizing cities in sub-Saharan Africa, is experiencing a deteriorating trend in air quality. This decline is driven by emissions from multiple diffuse local sources, including transportation, domestic and outdoor cooking, and industries, as well as by sources outside the city airshed, such as seasonal open fires in the region. PM_2.5 (particulate matter under 2.5 μm size) is the key pollutant of concern in the city with monthly spatial heterogeneity of 60–100 μg m⁻³. Outdoor air pollution is distinctly pronounced in the global south cities and lack the necessary capacity and resources to develop integrated air quality management programs including ambient monitoring, emissions and pollution analysis, source apportionment, and preparation of clean air action plans. This paper presents the first comprehensive integrated assessment of air quality in Kampala to define a multi-level intervention framework, utilizing ground measurements from a hybrid network of stations, global reanalysis fields from GEOS-Chem and CAMS simulations, a high-resolution (∼1 km) multi-pollutant emissions inventory for the designated airshed, WRF-CAMx-based PM_2.5 pollution analysis, and a qualitative review of the institutional and policy environment in Kampala. This collation of information documents baseline data for all known sectors, providing a foundational resource for the development of a clean air action plan. The proposed plan aims for better air quality in the region using a combination of short-, medium-, and long-term emission control measures for all the dominate sources and institutionalize pollution tracking mechanisms (like emissions and pollution monitoring and reporting) for effective management of air pollution.

The phase state of atmospheric particles impacts atmospheric processes like heterogeneous reactions, cloud droplet activation, and ice nucleation, influencing Earth's climate. Factors like chemical composition, temperature, and relative humidity govern particle phase states. The Arctic atmosphere is stratified, with varying particle compositions, but vertical profiles of submicron phase states remain poorly understood due to limited aloft measurements. To address this, particle samples were collected via a tethered balloon system (TBS) at the U.S. Department of Energy Atmospheric Radiation Measurement Program's facility at Oliktok Point, Alaska, on November 19, 2020. Using an environmental scanning electron microscope with a tilted Peltier stage to simulate atmospheric conditions, we probed particle phase states, observing near-spherical, dome-like, and flat shapes upon substrate impact. Particles at an altitude of 300 m contained similar, high fractions of viscous particles (79 ± 9%) compared to ground-level (74 ± 5%). Chemical characterization revealed that carbonaceous-rich and carbonaceous sulfate-rich particles dominate ground-level samples, while 300 m samples included more carbonaceous-rich and carbonaceous-coated dust particles. STXM-NEXAFS further highlighted differences in particle mixing states, with a higher abundance of organic and mixed organic–inorganic particles at both altitudes. Integrating chemical composition and phase state measurements demonstrated that carbonaceous-rich and organic-dominated particles exhibited higher viscosities, while inorganic-rich particles displayed lower viscosities. This finding establishes an association between composition and phase state, offering critical insights into the vertical stratification of Arctic particles.

Stabilised Criegee intermediates (sCIs), which are formed in the atmosphere through the ozonolysis of alkenes, are known precursors of sulphate aerosols (SO₄²⁻(p)). Several previous studies have focused on the kinetics of sCI-related chemistry using both experimental and theoretical methods. Nonetheless, detailed evaluations of how the sCI affects global-scale SO₄²⁻(p) formation using chemical transport models (CTMs) have rarely been conducted. In this study, the impact of sCIs on SO₄²⁻(p) and other particulate matter was estimated using a global CTM by implementing approximately 100 chemical reactions associated with CI chemistry. The results suggest that sCIs contribute maximally less than 0.5% in remote areas, such as Amazon rainforests, Central Africa, and Australia. This value is lower than the previously estimated value, despite certain kinetic parameters related to CI chemistry being provisional due to insufficient data. Future work should focus on obtaining these kinetic parameters through experimental studies or theoretical calculations. The sCI that contributed the most to SO₄²⁻(p) formation was E-methyl glyoxal-1-oxide, which was generated by the ozonolysis of methyl vinyl ketone owing to its low-rate coefficient for the loss reaction of unimolecular decomposition and water vapour. The change in SO₄²⁻(p) enhanced the formation of secondary organic aerosols, whereas the reactions of the sCIs with NO₂ decreased the formation of nitrate radicals. The results of the sensitivity analyses showed that in highly industrialised sites in China and India, OH radicals formed by the unimolecular decomposition of vibrationally excited CIs (vCIs) contributed to SO₄²⁻(p) formation, which maximally accounted for nearly ten times more than that of sCIs, whereas the contribution of vCIs and sCIs to SO₄²⁻(p) formation was estimated to be almost equal in rural and remote sites. The estimated sCI loss by HNO₃ and organic acids was comparable to that of the unimolecular decomposition of sCIs and scavenging by water. This study provides full insight into the impact of gas-phase CI chemistry on a global scale.

Correction for ‘Numerical one-dimensional investigations on a multi-cylinder spark ignition engine using hydrogen/ethanol, hydrogen/methanol and gasoline in dual fuel mode’ by Ufaith Qadiri, Environ. Sci.: Atmos., 2024, 4, 233–242, https://doi.org/10.1039/D3EA00139C.