ACS ES&T Air最新文献

Cloud droplets are known to effectively chemically process water-soluble organic compounds. Field measurements clearly show that concentrations of organic compounds measured in cloudwater can deviate significantly from predictions made with Henry’s law, with high enrichments measured for less water-soluble organic compounds. Several processes are suspected to be the cause of the observed enrichments, but the key process has not yet been elucidated. Here, we use the bulk-interface partitioning approach to predict enrichment coefficients (q) of organic compounds in cloud droplets. A predictive equation is derived as a function of the bulk-interface partition coefficients (K_p) and octanol–water partition coefficients (K_ow). The calculated enrichments are compared to measured q values from different field campaigns. The results show that the predicted values follow the same trend and absolute values as the measurements. Highly water-soluble compounds have small enrichments, with values around 1, while less soluble compounds have very high enrichments of up to >10³. A sensitivity study is performed for the range of K_ow values obtained from different models, and for the range of measurements for different measurement conditions. The results of the sensitivity study show that the q measurements and predictions lie within the same range, thus showing that bulk-interface partitioning can be a good predictor for organic enrichments in cloudwater.

This study presents a new approach describing the deviations of organic concentrations in cloudwater from Henry’s law using bulk-interface partitioning. This approach provides a simple but accurate estimation of the enrichment of various organic compounds in cloud droplets.

The agricultural sector significantly contributes to atmospheric pollution, impacting air quality through activities such as tillage, planting, fertilizer application, harvesting, crop residue burning, and grain handling. The outcome of this work is the documentation of the emission inventory of particulates (PM₁₀ and PM_2.5) and gaseous emissions (SO₂, CO, NO_x, NH₃, and volatile organic compounds (VOCs)) from the agricultural industry, particularly crop production. Further, the emissions of elemental carbon (EC), organic carbon (OC), and polycyclic aromatic hydrocarbons (PAHs), which are part of particulate matter (PM), were calculated along with greenhouse gases (CO₂, CH₄, and N₂O) coming from the agricultural sector for 2021, with projections for 2051. Total greenhouse gas emissions in 2021 were 408 Tg, while PM₁₀ and PM_2.5 emissions were approximately 2.5 and 1.1 Tg, respectively. The health impact of primary agricultural PM_2.5 was quantified, revealing an estimated approximately 4 million disability-adjusted life years (DALYs) and 0.13 million deaths attributable to these emissions in 2021. The findings highlight the urgent need to reduce emissions at their source and ensure sustainable agricultural practices. This study provides critical data for policymakers to address air quality and health challenges. Furthermore, the developed emission inventory will serve as a valuable resource for researchers conducting air quality modeling and environmental impact assessments.

Despite decades of ongoing mitigation efforts, ozone (O₃) levels remain persistently high in Houston, TX. For a high O₃ episode observed during the NASA Tracking Aerosol Convection Interactions ExpeRiment-Air Quality (TRACER-AQ) campaign, we use a high-resolution large-eddy simulation (LES) within the Weather Research and Forecasting model coupled with Chemistry (WRF-LES-Chem) to investigate temporal and spatial variations in O₃ formation regimes over the region. By leveraging improved simulations of O₃ and its precursors by LES, compared to the mesoscale WRF model, we derive and compare two O₃ sensitivity indicators: the formaldehyde-to-nitrogen dioxide ratio (FNR) and the ratio of radical loss via NO_X reactions to total primary radical production (L_N/Q). Specifically, we use L_N/Q to inform the threshold for FNR, the latter being a more commonly used and accessible indicator, although it is subject to significant uncertainties. We demonstrate that O₃ production in the Houston urban area transitions from a nearly homogeneous early morning VOC-limited regime to a NO_X-limited regime by midday. Using the L_N/Q indicator, we identify that a range of 0.6 < FNR < 1.8 falls in the transition zone of O₃ formation regime. The high-resolution modeling of O₃ formation and the FNR range developed in this LES study offers valuable insight for assessing future air quality and improving the understanding of atmospheric chemistry that underpins pollution control in Houston.

The oil sands (OS) region in Canada hosts one of the world’s largest unconventional crude oil deposits in the form of bitumen, which, when extracted, generates substantial tailings/wastewater that are stored in on-site ponds. Naphthenic acid fractional compounds (NAFCs), a complex mixture of alkyl-substituted acyclic and cycloaliphatic organic acids, are natural bitumen components known for their ecological toxicity and are concentrated during the extraction process into tailings ponds, where they are assumed to remain confined to the aqueous phase. Here, we quantify the emissions of up to 275 NAFCs to the atmosphere from a tailings pond and from facility-wide operations at major OS facilities. The results indicate that, despite the absence of NAFC air emissions in inventories, large quantities are emitted to the atmosphere, likely originating from surface photochemical and/or biodegradation processes. Emission rates across entire operations ranged from 3509 to 7286 kg h^–1, translating to annual emissions of 1163–2660 tonnes from both primary and secondary sources. The findings imply that NAFC air emissions may serve as a key pathway for these chemicals to enter the environment, potentially impacting downwind ecosystems.

Harmful chemicals called NAFCs found in bitumen were thought to remain in tailings ponds water. However, this study shows that large amounts─up to 2660 tonnes per year─escape into the atmosphere from Oil Sands operations

We present the seasonal variations of enhancement ratios (ERs, i.e., ΔNO_x/ΔCO₂ and ΔCO/ΔCO₂) as a function of distance from highways in the San Francisco Bay Area, using observations from the Berkeley Environmental Air Quality and CO₂ Network (BEACO₂N) at 40 locations. The spatial patterns exhibit exponential distance-decay relationships, with higher NO_x and CO ERs near highways and more uniform ERs at distances beyond 3 km. These patterns are used to infer emission factors (EFs) for transportation and residential buildings. BEACO₂N-derived EFs for CO (7.8 ± 0.6 ppbv/ppmv) and NO_x (1.0 ± 0.02 ppbv/ppmv) from transportation agree with inventory estimates. In contrast, the residential NO_x EF (0.15 ± 0.01 ppbv/ppmv) is four times lower than inventory estimates, and the residential CO EF (4.3 ± 0.3 ppbv/ppmv) is 33% lower than the California state inventory estimate.

Reactive oxygen species (ROS) play a central role in the chemical aging of organic aerosols and adverse aerosol health effects upon respiratory deposition. Previous research has shown that biogenic secondary organic aerosols (SOA) form ROS, including hydroxyl radicals and superoxide, via reactions of reactive compounds, including organic hydroperoxides and alcohols in the aqueous phase. However, the influence of oxidative aging and the SOA oxidation state on the ROS yield has not been systematically investigated. In this study, we quantify ROS yields in d-limonene SOA and β-caryophyllene SOA generated via ^•OH and ^•Cl oxidation in an oxidation flow reactor at equivalent atmospheric aging times ranging from 4 h to 22 days. We quantify radical formation using electron paramagnetic resonance spectroscopy combined with a spin-trapping technique and characterize the molecular composition of the SOA samples with high-resolution mass spectrometry. We observe maximum radical formation at an oxygen-to-carbon ratio (O/C) of ∼0.5. Thereafter, we observe a >90% decrease in radical yield as the O/C increases to 1.2 for both d-limonene SOA and β-caryophyllene SOA. Similarly, the radical yield in d-limonene and β-caryophyllene SOA is reduced by >80% after on-filter photoirradiation. Peroxide yields are found to decrease with increasing O/C values and irradiation, suggesting that the aging-induced fragmentation and/or photolysis of hydroperoxides contribute to a decrease of radical formation in aged SOA.

Household volatile chemical products (VCPs) have emerged as a significant source of volatile organic compounds (VOCs) in urban environments. This study uses a computational fluid dynamics (CFD) model, APFoam, which integrates a comprehensive ozone (O₃)─nitrogen oxide (NO_x)─VOCs photochemical mechanism, to qualitatively evaluate the influence of VCPs emissions on pollutant distributions in the regular canyons (i.e., aspect ratio, AR = 1). Compared to scenarios without VCPs emissions, VCPs emissions at levels comparable to traffic emissions lead to an approximately 60% increase in the concentration of O₃ within the street canyon. The pedestrian-level pollutant concentration and health risk were evaluated, suggesting that more nitrogen dioxide (NO₂) exposure was on the leeward side, while the levels of O₃ exposure were higher on the windward side, with health risk increasing by 1.6–2.2 times with increased VCPs emissions or reduced traffic emissions. A total of 39 emission scenarios, varying in traffic and VCPs emission strengths, were analyzed to assess different mitigation strategies, including traffic-only, VCPs-only, and combined reduction pathways (i.e., adjusting the traffic-to-VCPs emission ratio, T/V). The results indicate that the concentration of O₃ can be effectively reduced only when T/V = 1:5, suggesting that substantial reductions in VCPs emissions are necessary to mitigate pollution. This finding underscores the need for increased focus on VCPs controls, even in the context of vehicle electrification, as traffic reductions alone are insufficient to curb the level of O₃ pollution. The study provides critical insights for air quality management, emphasizing the importance of integrating VCPs emission controls into urban pollution mitigation strategies.

Missing sulfate production pathways have been implicated as the cause of model underestimates of sulfate during haze events in East Asia. We add multiphase oxidation of SO₂ in aerosol particles by H₂O₂, O₃, NO₂, HCHO, and O₂, catalyzed by transition metal ions (TMIs), to the GEOS-Chem model and evaluate the model with (1) year-round ground-based observations in Seoul, South Korea, (2) airborne observations from the KORUS-AQ field campaign, and (3) fall and winter ground-based observations in Beijing, China. Multiphase chemistry contributes 14% to 90% to total sulfate production depending on the location and season and increases model daily average sulfate by 2 to 3 μg m^–3, with maximum daily increases up to 12 μg m^–3. From winter to summer, oxidation pathways shift, with the largest fraction of multiphase sulfate production occurring during spring and summer due to oxidation by H₂O₂. Multiphase oxidation of SO₂ by the H₂O₂ pathway reduces gas-phase H₂O₂ concentrations by −40% in spring, which improves model agreement with H₂O₂ airborne observations. Oxidation pathways also shift between cities, in particular the contribution from the TMI and NO₂ pathways, which are more important in Beijing than in Seoul. This is due to higher levels of transition metals, and a larger impact of an overly shallow mixed layer in Beijing compared to Seoul. The implementation of multiphase aerosol chemistry in GEOS-Chem here allows for the use of this chemistry in other models that can address boundary layer errors, including WRF-GC and CESM-GC. The analysis presented here shows that this chemistry is important to the simulation of sulfate year-round, not only during haze events, and is unique in showing coupled gas- and aerosol-phase impacts of multiphase chemistry.

Air quality models typically do not include production of sulfate in humidified particulate matter. This study shows the importance of including this process in models to improve understanding of particulate pollution levels year-round.

Limonene is the fourth most emitted biogenic volatile organic compound and is often used as a fragrance and emitted from personal care products, cleaning products, and others. Chlorine gas (Cl₂), a precursor for Cl atoms, is emitted from anthropogenic activities, including cleaning, disinfection, and industrial activities, and it also forms from heterogeneous reactions involving sea salt. Thus, limonene and Cl radical precursors can both be present in indoor and outdoor environments. We studied the chlorine-initiated oxidation of limonene under indoor lighting (LED lights) and simulated outdoor lighting (a combination of UVA and LED lights) using an environmental chamber and a suite of instruments measuring gas and particle phase products. OH radicals formed and dominated the oxidation of limonene in the presence of NO_x, Cl₂, and LED lights, highlighting that Cl-initiated chemistry can generate OH chemistry in indoor environments, even in the absence of sunlight. Measurements from an iodide chemical ionization mass spectrometer showed gas phase reaction products from both Cl and OH addition to limonene, including nitrated species LIMANO₃ (C₁₀H₁₇NO₄) and LIMALNO₃ (C₁₀H₁₇NO₆). Secondary organic aerosol (SOA) yields were high, exceeding 1.1 in experiments with low NO_x and high limonene concentrations, and showed strong dependence on temperature, NO_x, and the VOC/Cl₂ ratio. These findings suggest that Cl₂ can contribute to the indoor and outdoor SOA formation from limonene oxidation through direct oxidation and secondary OH chemistry.

Ozonolysis of α-pinene is a significant and well-established source of atmospheric secondary organic aerosol (SOA), which plays a pivotal role in climate, air quality, and human health. The products of α-pinene ozonolysis measured experimentally are typically characterized by only their molecular formulas, while their structures and formation mechanisms often remain unclear. In this work, we theoretically map the oxidation pathways, structures, and formation time scales of the major first-generation products formed from α-pinene ozonolysis by calculating the H-shift and bond-scission reaction rate coefficients of the peroxy (RO₂) and alkoxy (RO) radicals that arise under atmospheric conditions with different RO₂ bimolecular reaction rates (k_bi): polluted (k_bi > 0.2 s^–1), moderate (0.2 s^–1 > k_bi > 0.01 s^–1), and pristine (k_bi ≈ 0.01 s^–1). In polluted environments, almost no RO₂ unimolecular reactions are of importance and ozonolysis leads to nitrates and small fragmented products. By contrast, in moderate to pristine atmospheres, C₁₀ highly oxygenated organic molecules (HOMs) with up to 12 oxygen atoms can form from either purely unimolecular or a combination of unimolecular and bimolecular reactions. Our results suggest that explicit chemical mechanisms of α-pinene ozonolysis used ubiquitously in the literature require significant revision in their treatment of unimolecular-isomerization and stereoisomer-specific reactions.