ACS ES&T Air最新文献

Products and mechanisms of atmospheric oxidation of volatile organic compounds (VOCs) are complex and depend on the VOC structure, oxidant, and oxidation regime. In addition to alkanes, alkenes, and aromatics, the major classes of hydrocarbons that are emitted to the atmosphere, oxygenated VOCs are also an important component of anthropogenic and biogenic emissions whose reactions can influence the formation of ozone and secondary organic aerosol. In this study, we investigated the effect of an ether group on the OH radical-initiated oxidation of dioctyl ether (DOE), a linear C₁₆ compound with an ether group located in the center of the carbon chain, under high NO_x conditions. Experiments were conducted in an environmental chamber, and gas- and particle-phase products were analyzed using gas and liquid chromatography, electron and chemical ionization mass spectrometry, infrared spectroscopy, and derivatization-spectrophotometry. Nitrate, hydroxynitrate, and hydroxycarbonyl ether products are analogous to those formed from the reaction of the corresponding alkane; however, the dominant product was octyl formate formed exclusively by reactions involving the ether group. Measured product yields were used with structure–activity relationships for OH and alkoxy radical reactions and literature branching ratios for the corresponding alkane reaction to determine the effect of the ether group on the branching ratio for nitrate vs alkoxy radical formation and to develop a simple model that predicted product yields in reasonable agreement with measurements. Compared to the corresponding alkane, the presence of the ether group increases OH reactivity, decreases the nitrate yield, and reduces the SOA yield by enhancing the formation of alkoxy radicals that decompose rather than isomerize to form low-volatility multifunctional products.

Indoor air quality was monitored in a variety of public buildings during the wildfire seasons of 2019 and 2020 in Missoula, MT, to better understand what factors impact smoke infiltration indoors. PurpleAir sensors were used indoors and outdoors to calculate indoor/outdoor (I/O) PM_2.5 ratios that were compared with building characteristics. Wildfire smoke concentrations measured indoors during a 7 day smoke event were always lower than outdoors, but some buildings had up to 4 days of PM_2.5 above 55 μg/m³, corresponding to an unhealthy air quality index. Locations with heating, ventilation, and air conditioning (HVAC) systems in excellent condition and with tightly fitting filters had lower I/O ratios than locations with HVACs in poor condition or locations without an HVAC system. On average, I/O ratios were 15% higher during building open hours compared to closed hours, which may have been due to increased HVAC operation and more frequent door opening during open hours. The I/O ratios ranged from 0.29 to 0.97, varying across locations and during different conditions (presence of smoke or cold weather). No single building factor was identified as being most important in reducing indoor PM_2.5; therefore, indoor PM_2.5 measurements are essential for identifying when additional mitigation measures are needed.

The COVID-19 pandemic highlighted the importance of indoor air quality and the role of airborne transmission in the disease spread. Heightened public awareness led to an increase in the commercialization and use of air cleaners. While several of these devices effectively disinfect the air, some also initiate chemical reactions that can worsen indoor air quality by generating ozone (O₃) and other harmful air pollutants. Here we demonstrate the use of a MnO_x-based catalyst to mitigate both air cleaner-generated and ambient pollution in a university office. We deployed two real-time chemical ionization mass spectrometers alongside a suite of air quality analyzers to measure a wide range of volatile organic compounds (VOCs), other trace gases, and particles. We show the reduction of many indoor pollutants in a combination of real indoor environment and atmospheric chamber experiments, including O₃, nitrogen oxides, formaldehyde, and other oxidized VOCs. We observed an increase in the concentrations of more reduced VOCs with catalyst use. We demonstrate that over 24 weeks of continuous operation, the clean air delivery rate of the catalyst for O₃ pollution declined linearly by 20%. These findings suggest that employing a dedicated catalyst could reduce indoor air pollution and enhance the human health benefits of air cleaners by minimizing the associated indoor air quality risks.

This paper reports on the mitigation of ambient and air cleaner-generated indoor air pollution using a dedicated catalyst.

Site-level aerial surveys, while effective in detecting CH₄ emissions from upset conditions, face challenges to provide comprehensive long-term emission estimates due to their snapshot measurements, emissions variability, and minimum detection limits. Conversely, annual inventories submitted by operators often exclude emissions from failure events and unregulated sources, leading to incomplete emission estimates. This study introduces a novel methodology that utilizes the Mechanistic Air Emissions Simulator (MAES) to integrate two highly variable estimation methods: inventory and aerial methods. The proposed methodology identifies and characterizes failure events with site-specific information, thereby enhancing the accuracy of inventory programs through the so-called measurement-informed inventories (MIIs). Furthermore, it emphasizes the importance of carefully comparing instantaneous emission measurements from aerial surveys with annual average emissions reported in inventories, as they have distinct timeframes. Colorado State University (CSU) collaborated with the Colorado Department of Public Health and Environment (CDPHE) to utilize this approach to enhance reported emissions from the upstream sector in Colorado Denver-Julesburg (DJ) basin. This initiative is part of Colorado's Upstream greenhouse gas (GHG) Intensity Program, a regulatory initiative that requires oil and gas (O&G) operators to monitor, report, and reduce GHG emissions. The goal was to incorporate measured emissions from failure events conducted by Carbon Mapper (CM) in the simulations to derive a multiplier that rectifies for potential omissions of emissions from abnormal conditions within the O&G sector. To simplify the simulation process, prototypical sites were defined in conjunction with operators and are used to represent groups of O&G facilities in the basin with similar configuration. The outcomes of this work indicate that inventories are likely underestimating total emissions, as an additional 16.4% of total emissions from abnormal events is estimated for the basin. This estimate may represent a lower bound, as the survey technologys detection limit may exclude most CH₄ emission events below 50 kg/h.

Aerial and inventory methods often miss methane emissions from abnormal oil and gas site events. This study improves estimates by integrating both methods, revealing higher total emissions with regulatory implications.

The partitioning between inorganic salts and organic compounds within individual particles is a key factor that influences the uptake of water by particles. In this study, we investigated the aerosol hygroscopicity of ammonium sulfate (AS) and 2-methylglutaric acid (2-MGA) mixtures. 2-MGA is a moderately surface-active compound. Dilute surface tension measurements of 2-MGA/AS mixtures were taken by using a pendant drop goniometer. Hygroscopicity at subsaturated conditions was determined using a hygroscopicity tandem differential mobility analyzer (H-TDMA) and relative humidity was kept constant at 89 ± 0.9% RH. The droplet activation was also measured at supersaturated conditions using a cloud condensation nuclei counter (CCNC) from 0.4 to 1% supersaturation (SS). The single-hygroscopicity parameter κ was derived from measurements. Mixtures predominantly composed of AS, up to a 60 wt% 2-MGA, exhibit κ-values close to pure AS. However, κ decreases significantly as the organic fraction increases (>60 wt% 2-MGA). Previous predictions of κ-hygroscopicity assume full dissolution of both the organic and inorganic compounds. However, organic partitioning can influence the κ-hygroscopicity. A coverage-based parametrization, ϕ, assumes the probability of surface-active organics at the droplet surface. By estimation of the bulk and surface organic contribution, overall κ-hygroscopicity can be calculated. The model is computationally efficient, and the results indicate that organic solute depletion should be considered for fully soluble surface-active organics. Hygroscopicity predictions that account for the role of organic surface-active partitioning agree best with experimental results (R² > 0.95). Therefore, this study helps to enhance our understanding of cloud-forming properties of complex chemical mixtures containing surface-active organic and inorganic compounds.