ACS ES&T Air最新文献

This study investigated the coevolution of the light-absorption properties of biomass-burning primary and secondary organic aerosol (POA and SOA) during photochemical aging. We performed smoldering combustion of duff and photochemically aged the emissions in an oxidation flow reactor (OFR). We retrieved the imaginary part of the refractive index (k) of the POA, aged POA (APOA), SOA, and aged OA (AOA), which includes both APOA and SOA. Photochemical aging induced competing effects on AOA absorption: (1) slight photoenhancement in POA, and (2) formation of very weakly absorbing SOA, with midvisible k an order of magnitude smaller than that of the POA, that photobleached rapidly with further oxidation. The latter effect dominated, resulting in a net decrease in AOA absorption. Changes in chemical composition corroborated the evolution in light-absorption properties. While POA exhibited minimal change in chemical composition due to photochemical aging, SOA underwent significant chemical transformation consistent with the observed photobleaching. We also demonstrated that the previously used indirect method, which estimates SOA absorption by subtracting fresh POA absorption from AOA absorption, can lead to severe overestimation of SOA absorption. Our findings underscore the importance of considering the distinct optical evolution of SOA and POA during photochemical aging.

Many greenhouse gas (GHG) emission reduction measures achieve simultaneous reductions in air pollutants. Human-Earth system models can estimate such emission changes in the energy system but using them in chemistry-transport models (CTMs) to study their air quality impacts involves resource-intensive emissions processing. This is greatly simplified by an emissions scaling approach linking state-level emissions estimated by a human-Earth system model to a CTM. A scenario continuing pre-2022 energy policy in the U.S. to 2050 shows widespread air quality improvements over the 2015 baseline from SO₂ and NO_x emission reductions of 50 - 80% from electricity generation and light-duty vehicles. Scenarios of GHG mitigation and vehicle electrification at the state and national level add further benefits. However, PM_2.5 increases from increased use of wood heating and bioenergy suggest that additional PM_2.5 management may be needed when using biofuels. This approach helps assess multiple future energy scenarios efficiently without sacrificing chemical detail in the air quality simulations.

We investigated airborne concentrations of polychlorinated biphenyls (PCBs) near the Portland Harbor Superfund Site (PHSS), a historical and culturally significant location. In collaboration with residents, we measured airborne PCBs using polyurethane foam passive air samplers (PUF-PAS) deployed for 6 weeks. Additionally, we estimated PCB emissions based on the flux calculations from Portland Harbor (PH) water using PCB concentrations reported by the U.S. EPA to predict airborne PCB concentrations with an atmospheric dispersion model (AERMOD). Measured airborne total PCB concentrations ranged from 70 to 910 pg m^-3 with a geometric mean of 330 pg m^-3, which is lower than concentrations observed in other known PCB-contaminated areas in the U.S. Air congener distributions resembled commercial Aroclor mixtures 1016 and 1242, and estimated PCB flux from the water averaged 450 ± 120 ng m^-2 d^-1. Predicted airborne PCB concentrations ranged from 1 to 124 pg m^-3, with enrichment in non-Aroclor congeners when PH water is the sole source. However, all predicted concentrations were lower than measured values and exhibited different congener distributions, suggesting that PCB flux from PH water contributes only a minor portion (∼2%) of Portland's airborne PCB burden, and that additional PCB sources exist within the community.

Quantifying facility-level methane (CH₄) emissions is an important task for measuring progress toward net zero and carbon emission reduction targets. Landfills are a significant source of anthropogenic CH₄ emissions in Canada. Quantifying Canadian landfill emissions is also critical for validating assumptions in bottom-up inventory calculations but is a challenging task because of their variability in emissions sources and complex topography on and near landfill sites. We compare CH₄ emissions estimates for seven different emissions quantification strategies and platforms at a large landfill in Southern Ontario, Canada. We compare ground-based, aircraft-based, and satellite-based remote sensing techniques in addition to ground-based stationary, mobile, and aircraft-based in situ observation strategies across a 3.5-year period, including a 28-month deployment of a low-precision sensor network for continuous monitoring. Each methodology quantified a large range of emissions rates that vary by 1 order of magnitude for the site (∼200-2000 kg·h^-1), and the average estimated emissions rates agree within uncertainty. We find that the remote sensing methods have a higher empirical minimum detection limit and are sufficient for quantifying 20-50% of all Canadian landfill sites, while ground-based in situ methods have detection limits suitable for quantifying emissions from the majority of accessible landfill sites.

Air cleaning devices, or "air cleaners", have the potential to improve indoor air by decreasing levels of air pollutants, including volatile organic compounds (VOCs), in indoor environments. Many commercial air cleaners aimed at removing VOCs adopt chemically active technologies, such as oxidation-based chemistry, in addition to (or instead of) physical removal. However, these technologies risk forming unwanted oxidation byproducts that may cause adverse health effects, which can offset (or even outweigh) the benefits of decreasing the number of VOCs. Studies characterizing byproduct formation are generally limited; most such studies were restricted to a single or a few model VOC species as challenge compounds. The composition of indoor air, however, can be highly complex, containing a variety of VOC classes that may not be well represented by a few model species. Here, we present a case study in which we challenge an oxidation-based air cleaner (which uses photoelectrochemical oxidation) with a real-world VOC mixture emitted from spraying a commercial air freshener. This mixture contains a complex suite of organic compounds commonly found in indoor environments, including organic solvents (most importantly ethanol), fragrance agents, and other hydrocarbons and oxygenates of various molecular sizes. Experiments were conducted in a controlled environmental chamber with a suite of real-time analytical instruments to measure the identity and concentration of a wide range of VOCs. We find that the VOC composition changes drastically within a few hours due to running the air cleaner, characterized by the decrease in ethanol and large species (those with 4 or more carbon atoms) and the formation of C₁-C₃ oxygenated byproducts; no large oxidation products are observed. A substantial fraction of ethanol (and possibly other VOCs) is converted to acetaldehyde and formaldehyde, whose levels were observed to increase over the course of several hours during the operation of the air cleaner. Our results suggest the importance of ethanol, a ubiquitous VOC in indoor air, in evaluating the benefits and risks of indoor air cleaners, as ethanol can be efficiently oxidized to byproducts known to negatively impact human health.

Removal of gases and particles by precipitation (wet deposition) is a critical process that significantly influences the transport and chemical transformation of atmospheric compounds. However, there are few studies that directly measure or constrain the rates of this process under real-world conditions. This work quantifies the net change in ambient concentrations during precipitation events (removal rates) of gas- and particle-phase organic compounds at a surface site near Manaus, Brazil, during the GoAmazon2014/5 campaign. Removal rates of identified and unknown compounds that have been previously classified into source-based clusters are measured during rain events and categorized based on estimated properties of compounds and clusters. Highly oxygenated gases, such as isoprene oxidation products, are removed during precipitation events with a median removal rate of 0.09 h^-1 and the fastest analyte is removed at a rate of 0.22 h^-1. Removal rates of particle-phase compounds are observed at roughly this median rate, while less soluble gases, such as terpenes, exhibit low removal rates. These results are roughly in agreement with prior theoretical estimates of wet deposition rates for comparable compounds, providing an empirical point of comparison while noting that our metric reflects the net influence of precipitation events rather than wet deposition alone.

The reaction of ozone (O₃) with iodide and dissolved organic carbon (DOC) in the sea surface microlayer is a major pathway for O₃ loss from the troposphere. The impact of O₃ dry deposition to freshwater surfaces (e.g., inland lakes) is understudied, where current regional air quality models are unconstrained by experimental measurements of O₃ deposition rates. Since iodide concentrations in lake water are typically negligible, O₃ reactions at these surfaces are likely controlled by the reaction of O₃ with DOC. This study aims to better constrain the reactive loss of O₃ to inland waters by measuring the reactivity of O₃ with samples collected from freshwater lakes in Wisconsin and Michigan. We find that the reactivity of O₃ to lake water is comparable to seawater and suggest that the O₃ dry deposition rate can be parametrized as a function of lake water DOC concentration. Calculated deposition velocities and the resulting O₃ loss rates highlight that dry deposition to freshwater lakes reduces net production of O₃ particularly in shallow boundary layers.

Sulfur hexafluoride (SF₆) is a highly potent greenhouse gas with a Global Warming Potential (GWP) of 24,700 over 100 years and is globally mainly used as an electrical insulator in switchgear. Several measurement networks have tracked SF₆ for many years and their European data reveal significant emissions in southern Germany. This study focuses on German SF₆ emissions (2020-2023), using atmospheric measurements from 22 European sites, offering high spatial and temporal resolution for robust emission assessments. While German UNFCCC inventory bottom-up emission estimates report a major source of SF₆ through the disposal of soundproof windows, the spatial distribution of German SF₆ emissions derived on top-down inversion techniques (InTEM and Flexinvert+) reveals a different picture: The continuous pattern of high emissions from a particular region is responsible for one-third of total SF₆ emissions in Germany. Despite this, total German SF₆ emissions have decreased from 112 ± 26 t in 2020 to 89 ± 15 t in 2023 (InTEM), with estimates from all methods (both bottom-up and top-down) showing similar trends. Our findings suggest that the emissions from soundproof windows are overestimated, while industrial sources - particularly from SF₆ production and recycling in the focus region - are likely underestimated.

Biogenic volatile organic compounds (BVOCs) emitted from aquatic systems are increasingly recognized for their influence on atmospheric chemistry. However, emissions from freshwater environments, specifically during harmful algal bloom (HAB) events, remain poorly quantified. These HAB events are increasing globally in frequency and intensity, driven by climate change, nutrient runoff, and land-use changes. This study investigates the water-to-air gas exchange rates of BVOCs from southwestern Pennsylvanian freshwater lakes during peak HAB conditions, with a focus on nitrogen-containing compounds that are typically underrepresented in atmospheric measurements. Using atmospheric pressure, hydronium chemical ionization mass spectrometry (CIMS), we measured BVOC emissions from 18 lake samples in the laboratory, capturing real-time fluxes of 900 unique masses. Ammonia, pyrroline, and pyridine consistently exhibited the highest emission fluxes across samples. Alkylamines were less abundant, although they remain atmospherically important due to their role in new particle formation. These results represent the first reported real-time freshwater flux measurements of alkylamines, pyrroline, and pyridine, offering new insight into the atmospheric implications of HABs. Notably, no clear correlation was observed between BVOC fluxes and chlorophyll a and phycocyanin concentrations, which were taken to represent the cyanobacterial concentrations in the samples. This suggests that emissions are influenced by other biological or chemical factors not captured in this study. Principal component analysis identified two significant outlier water samples, driven by elevated ammonia, pyrroline, and an unknown compound at 124.101 amu, though the underlying cause of these deviations remains unresolved. The remaining lake emissions were similar. These findings provide foundational observations to better understand the role of freshwater system emissions in regional air quality and atmospheric processes.

Periodic leak detection and repair (LDAR) surveys are a key part of most modern oil and gas sector methane regulations, however their effectiveness in real-world practice has been difficult to assess. This study analyzes three years of reported data from regulated LDAR surveys in British Columbia, Canada, which suggest that 3×/year optical gas imaging (OGI)-based LDAR surveys reduce detected emissions by half at fully compliant sites. However, independent source-resolved aerial surveys at an identical subset of sites find 12 times more methane emissions overall, and four times more emissions after conservatively excluding potential combustion-related and intentional vent sources not targeted by OGI LDAR surveys. This demonstrates that regulated OGI-based LDAR surveys only capture a small portion of total emissions in practice, raising concerns about overestimated mitigation impacts and potentially misguided expectations when assessing alternative technologies. Further analysis reveals the two methods find complementary subsets of sources, with aerial detections comprising a range of larger combustion, vent, and fugitive sources and LDAR detections dominated by numerous smaller leaks from connectors and valves. This underscores the importance of integrating complementary measurement approaches to capture the full distribution of emissions and the necessity of independent verification frameworks such as OGMP 2.0.