ACS ES&T Air最新文献

Global aviation has contributed ∼3.5% to the anthropogenic climate forcing in 2018, of which around two-thirds (with substantial uncertainty) were due to non-CO₂ effects dominated by contrail cirrus. To be sustainable, the aviation industry faces a great challenge in reducing its climate footprint. There are ongoing efforts toward contrail avoidance via rerouting flights to avoid ice supersaturated regions, but serious reservations have been voiced against it because of extra fuel burning and resultant increased CO₂ emissions, among other issues. Based on simulations with a state-of-the-art aerosol and contrail microphysics model, we show that the aviation non-CO₂ climate effect associated with contrail cirrus may be significantly reduced via controlled seeding of a small amount of ice-nucleating particles (INPs). The optimized amount of INPs seeded will consume water vapor and minimize the peak relative humidity reached in the plume. In turn, this reduces the number of exhaust particles activating and forming contrail ice particles by up to 1-2 orders of magnitude, resulting in larger contrail ice particles that fall faster and shorter contrail lifetimes, which is expected to diminish the warming effect of contrail cirrus to a very small level. This novel approach may solve some of the issues associated with the proposed navigational contrail avoidance, but further research is needed to assess its feasibility and environmental impacts.

Bioaerosols can affect human and plant health as well as climate. New automatic bioaerosol monitors capable of detecting and classifying pollen and fungal spores in real time have recently been developed, revolutionizing the way how data are collected, analyzed and distributed to the public. However, the technologies, still being very new, have not been adequately characterized and the instruments' performance is poorly understood. Here, we developed a general method for evaluating the performance of both the hardware (particle detector) and software (machine learning algorithm) of automated bioaerosol monitors. For the first time, number concentration measurements were carried out for particle sizes up to 70 μm. To do this, three different reference methods were combined: a custom-made reference optical particle counter, an inkjet aerosol generator (IAG) and particle tracking velocimetry (PTV). The size-dependent counting efficiency and unit-to-unit variability of five different SwisensPoleno Jupiter bioaerosol monitors was thus determined in a traceable manner over almost the entire pollen and fungal spore size range. The classification efficiency of the supervised machine learning (ML) algorithm developed by MeteoSwiss, which is currently being used by various research institutes and monitoring stations in Europe, was determined by delivering well-known pollen taxa to the Poleno monitor under controlled laboratory conditions. The influence of factors, such as environmental conditions and geographic location of the tree, on the classification efficiency was quantified, and recommendations are made for improving ML algorithm training in the future. The methods outlined in this study aim to establish a traceable framework to ensure that real-time bioaerosol measurements, despite the measurement challenges related to large micrometre-sized particles at low concentrations (a few hundred particles per m³), are carried out at the same level of accuracy as legislated air-quality measurements. This is particularly important as a step toward their integration into European legislation.

Sources of desert dust, atmospheric transport, recorded concentrations of atmospheric particulate matter (PM), physical, compositional, and biological characteristics, and likely direct and indirect impacts on air quality impairment are reviewed without a systematic, but with an expert approach. The aim is to offer information necessary to protect the health of exposed populations in the dust-emitting and dust-receptor regions. This review corroborates the complexity of the process by which air quality is impaired during dust episodes, the mixture of components that PM might contain during dust episodes, the differences between dust emission and reception regions, and the interplay of indirect effects (thinning the boundary layer; concentration of local pollution; interactions with anthropogenic pollutants). Based on these dust episode patterns, we recommend the implementation of alert systems to protect the more vulnerable members of the population and highlight a number of recommendations for air quality monitoring during such episodes to provide adequate data sets to rigorously evaluate health outcomes associated with dust exposure in emitting and receptor regions and the possible causes for these effects.

The Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) characterized aerosol composition using measurements at two sites within 3 km (Scripps Pier and Mt. Soledad) from 15 February 2023 to 14 February 2024. Comparing the two sites shows the strong influence of upwind sources that results in similar monthly compositions at both sites. The seasonal changes in chemical mass concentrations were largely driven by the upwind source regions, with coastal northwesterly back-trajectories occurring 63-65% of the year and bringing submicrometer mass concentrations that were lower than the EPCAPE average for all trajectories at each site. In contrast, refractory black carbon (rBC) and nonrefractory (NR)-organics and nitrate mass concentrations exceeded EPCAPE average concentrations for back-trajectories from urban areas such as Los Angeles-Long Beach. For hourly measurements, NR-organics and non-sea-salt (NSS)-sulfate mass concentrations at Mt. Soledad were correlated strongly (r = 0.73-0.82) to those measured at Scripps Pier, but NR-nitrate was correlated only moderately (r = 0.63). The explanation for the lower correlation of NR-nitrate is both emissions between the sites and semivolatility, with semivolatility accounting for site-to-site changes in daily averages of +0.01 μg m^-3 per percentage site-to-site difference in relative humidity and -0.07 μg m^-3 per degree Celsius site-to-site difference in temperature. On average, comparing Scripps Pier to Mt. Soledad, NR-nitrate was higher by 29% because of relative humidity and lower by -26% because of temperature. NR-nitrate and rBC mass concentrations at Scripps Pier for nighttime were 13-15% higher than those for daytime because land breezes brought higher inland concentrations. Concentrations of rBC were 52% higher at Mt. Soledad than those measured at Scripps Pier, accompanied by increases in tracers for brake wear because of traffic on the steep roads within 10 m of that site. The implications are that these nearby sites had comparable monthly concentrations of measured components due to their similar back-trajectories, but hourly and daily concentration differences supported quantification of the meteorological effects from relative humidity and temperature on semivolatile NR-nitrate as well as minor differences from land-sea breezes and local emissions.

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.

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.