Environmental science: atmospheres最新文献

Traffic as an important part of the energy sector significantly contributes to global air pollution. To mitigate the hazardous components of traffic emissions regulations have been implemented resulting in technological solutions such as exhaust after-treatment systems. However, fuels also play a crucial role in emissions and components such as the aromatic compounds in fuel have been linked to increased exhaust emissions. Several current emissions regulations neglect environmental factors, such as cold operating temperatures, that can significantly increase emissions. Moreover, the effect of fuel aromatics and cold temperature on emissions toxicity has not been adequately studied. This study evaluates the impact of after-treatment systems, aromatic fuel content, and cold operating temperature on emission toxicity. To achieve this, four different light-duty vehicles were used in a temperature-controlled dynamometer room, with a co-culture of A549 and THP-1 cell lines exposed to online exhaust emissions using a thermophoresis-based air–liquid interface (ALI) system. The results demonstrate that the aromatic content of both diesel and gasoline fuels increases exhaust toxicity. The study additionally emphasises the potential of particulate filters as after-treatment systems to reduce the toxicity of emissions and highlights how cold running temperatures result in higher exhaust toxicity. The study also assessed the diesel particulate filter (DPF) active regeneration event, which leads to multi-fold emissions and higher toxicological responses. Overall, the study provides crucial novel results on how various factors affect the toxicity of exhaust emissions from modern light-duty vehicles, providing insights into decreasing the emissions from this energy sector.

The light absorbing component of organic aerosols, brown carbon (BrC), directly affects climate and can play a role in the oxidative aging of organic aerosols. Recent estimates suggest that globally BrC may have a warming potential that is approximately 20% that of black carbon, and photochemistry from BrC compounds can increase or transform aqueous SOA. Photobleaching of BrC is estimated to occur with a timescale of hours to days, a range that complicates estimates of the effects of BrC on climate and aerosol chemistry. The chemical environment (e.g. pH, ionic strength, and non-BrC organic content) of aqueous aerosols can also affect the reactivity of BrC, potentially altering absorption spectra and reactions of excited states formed upon irradiation. A range of solar illumination sources have been used in studying the photochemistry of BrC compounds, making direct comparisons between results difficult. Higher energy, single wavelength studies (e.g. 308 nm) show much larger quantum yields than broadband studies, indicating wavelength dependent quantum yields for a wide range of atmospherically relevant substituted aromatics. In this work we investigate the wavelength dependence of the quantum yield for loss of a prototypical BrC compound found in wildfire emissions, vanillin, using several narrow band UV-LEDs that span the 295–400 nm range. These wavelength dependent quantum yields will allow a more direct comparison between photochemical experiments with laboratory irradiation sources and actual actinic fluxes. Vanillin photochemical loss rates are concentration-dependent due to direct reaction between triplet excited state and ground state vanillin molecules. The quantum yield for photochemical loss of vanillin can be approximated by a Gaussian decay from 295 nm to ∼365 nm. This function is used to directly calculate the solar zenith angle (SZA) dependence for photochemical loss. Computational results show the presence of two π → π* transitions responsible for the observed UV-vis spectrum and that the rate of intersystem crossing has a wavelength dependence remarkably similar to that of the quantum yield for loss. A strong kinetic salt effect is observed, showing a doubling of the loss rate at high ionic strength.

Top-down (atmospheric measurement-based) methane fluxes from individual emitting facilities are needed to reduce uncertainties in the global methane budget. This typically requires in situ methane mole fraction ([CH₄]), traditionally measured using high-precision optical sensors. We show that the semiconductor-based Figaro Taguchi Gas Sensor (TGS) is a cheaper alternative. Two TGS loggers were deployed near a landfill site. Logger-1 uses a pumped cell, containing one TGS 2602, two TGS 2611-C00 and one TGS 2611-E00; laboratory testing showed methane, ethane, carbon monoxide and hydrogen sulphide sensitivity for each TGS. Logger-2 uses an external fan, containing one TGS 2611-C00. The tested TGS 2611-C00 and TGS 2611-E00 units could yield [CH₄] during landfill deployment, by first modelling a reference baseline resistance in field conditions, representative of background (reference) [CH₄] sampling. Background sampling was identified using wind direction from a designated background segment, which yielded a baseline resistance model as a function of time (incorporating long-term background effects), water mole fraction and temperature. The ratio between measured TGS resistance and modelled baseline resistance was converted into [CH₄], using a two-term modified power fit. Logger-1 methane fitting coefficients were derived during laboratory testing, while Logger-2 coefficients used a 1.49% field sampling subset, alongside a high-precision reference (HPR) instrument. Reconstructed minute-averaged Logger-2 [CH₄] for TGS 2611-C00 was compared to the HPR up to 31.5 ppm [CH₄] (excluding [CH₄] fitting data), resulting in a ±0.55 ppm [CH₄] root-mean squared error (RMSE), for 295.2 overall sampling days (excluding data gaps). Reconstructed Logger-1 [CH₄] RMSE compared to the HPR was ±0.67 ppm and ±0.77 ppm for the two TGS 2611-C00 and ±1.17 ppm for the TGS 2611-E00, up to 29.3 ppm [CH₄], for 147.9 overall sampling days. Field TGS 2611-C00 superiority above other Logger-1 sensors is supported by laboratory tests, which showed TGS 2611-C00 to be most methane-sensitive. In summary, we show that the TGS 2611-C00 is an ideal low-cost sensor to measure [CH₄] from facility-scale sources, with a field RMSE below ±1 ppm. This work represents the first application of TGS resistance ratios to yield parts-per-million level [CH₄] field measurements, using a dynamic baseline resistance model.

Fine particulate matter (PM_2.5) resulting from wildland fire is a significant public health risk in the United States (U.S.). The existing stationary monitoring network and the tools used to alert the public of smoke conditions, such as the Air Quality Index or NowCast, are not optimized to capture actual exposure concentrations in impacted communities given that wildland fire smoke plumes have characteristically steep exposure concentration gradients that can vary over fine spatiotemporal scales. In response, we developed and evaluated a lightweight, universally attachable mobile PM_2.5 monitoring system to provide supplemental, real-time air quality information during wildfire incidents and prescribed burning activities. We retroactively assessed the performance of the mobile monitor compared to nearby (100–1500 m) stationary low-cost sensors and regulatory monitors using 1 minute averaged data collected during two large wildfires in the western U.S. and during one small, prescribed burn in the Midwest. The mobile measurements were highly correlated (R² > 0.85) with the stationary network during the large wildfires. Further, 1 minute averaged mobile measurements differed from three collocated stationary instruments by <25% on average for fourteen out of fifteen total passages. For the small, prescribed burn, rapidly changing conditions near the fire border complicated the comparison of mobile and stationary measurements but the spatial maximum concentrations measured by both instruments were consistent. In general, this work highlights the value of using portable sensor technologies to address the monitoring challenges presented by dynamic wildland fire conditions and demonstrates the value in combining mobile monitoring with stationary data where possible.

Airborne trace elements (TEs) from the development of the Athabasca bituminous sands (ABS) in northern Alberta, occur in coarse and fine aerosols. Here, TEs in Sphagnum moss and acid soluble ash (ASA, obtained by leaching ash for 15 min using 2% HNO₃) are used to estimate the distribution of TEs between these two aerosol fractions. Total concentrations of all elements increase toward industry, but chemical reactivity of the ash varies. Most of the Al is acid soluble, but most of the Th is not; the former is assumed to reflect the abundance and reactivity of light minerals, and the latter is a surrogate for heavy minerals. In the ASA, the trends in Ni and V, the dominant metals in bitumen, resemble Al. In contrast, Mo (also enriched in bitumen), plus Pb, Sb and Tl, are more like Th in exhibiting limited reactivity. Trace element enrichments in both the total and ASA fractions, relative to crustal abundance, are restricted to plant micronutrients (e.g., Cu, Mn, Mo, Zn), or elements that are passively taken up by plants (e.g., Cd and Rb, but apparently also Ag and Re). The greatest enrichments of TEs occur at the reference site, even though it is located 264 km from the centre of industrial activities. The ash of moss collected nearest industry is dominated by quartz (67%) which explains the low concentrations of TEs, absence of enrichment relative to crustal abundance, and limited chemical reactivity of Pb, Sb and Tl. In this region, total concentrations of TEs in moss are a poor guide to their bioaccessibility in the environment.

Increasing recognition of the significant contributions secondary organic aerosols can make in marine environments has led to an increase in research focused on understanding the reactions controlling their formation. Most marine laboratory studies to date have focused on the oxidation of individual volatile organic compounds (VOCs), particularly dimethyl sulfide (DMS). Thus, a lack of understanding exists in how complex marine VOC mixtures affect secondary marine aerosol formation and composition. To address this gap, we conducted controlled lab experiments that compare the effects of oxidizing single common marine VOCs versus VOC mixtures on secondary marine aerosol production. We used a potential aerosol mass oxidative flow reactor to investigate marine-relevant VOCs, including DMS, dimethyl disulfide (DMDS), and isoprene. Ion chromatography, chemical ionization mass spectrometry, aerosol time-of-flight mass spectrometry, and particle sizing instruments were employed to study how these mixtures influence the overall composition of marine aerosols. Our findings reveal that mixtures significantly alter the production and composition of secondary marine aerosols. Specifically, we found that isoprene, when oxidized in the presence of DMS and DMDS, affects methanesulfonic acid (MSA) and sulfate ratios, as well as overall aerosol yields. These insights suggest further studies on realistic marine VOC mixtures will help understand and predict the dynamics of secondary marine aerosol formation, therefore improving air quality and climate models and enabling more accurate predictions of marine aerosol impacts on cloud formation and properties.

Entrainment-mixing processes of fog with the surrounding ambient air are extremely intricate and impose significant effects on the microphysical and radiative properties of fog. However, it is difficult to utilize the default Thompson scheme of the atmospheric chemistry model GRAPES_Meso5.1/CUACE to examine the effects of different entrainment-mixing mechanisms on the microphysical and radiative properties of fog. To address this issue, this scheme is modified to include homogeneous mixing degree to investigate the effects of various entrainment-mixing processes on typical regional fog simultaneously occurring in the Northeast China and Yangtze River Delta regions from December 31, 2016, to January 2, 2017, and from January 6 to 8, 2017. It is revealed that inhomogeneous entrainment-mixing processes can result in smaller fog droplet number concentration and lower liquid water path, and larger fog droplet size. These phenomena, in turn, can lead to a decreased fog optical thickness and increased visibility. Furthermore, the effects of inhomogeneous entrainment-mixing processes depend on fog thickness, i.e., the effects in thin fog in the Northeast China region are more significant than those in thick fog in the Yangtze River Delta region. This primarily occurs because the proportion of evaporated grids in thin fog is higher than that in thick fog by 16% and 6%, respectively. These findings enhance the theoretical understanding of entrainment-mixing processes and lay the foundation for improving model parameterization.

Carbon monoxide has long been known as an indoor air pollutant, but has rarely been in the focus of scientific interest. This circumstance is certainly disadvantageous for the health-related assessment of indoor air quality, because exposure to carbon monoxide is often associated with serious or fatal poisoning. From an analytical perspective, the problem is that increased carbon monoxide concentrations often occur unexpectedly and within a short period of time, usually in connection with incomplete combustion processes. Therefore, the exposure of the general population to carbon monoxide cannot be determined using environmental surveys. In recent years, however, carbon monoxide has again received significantly greater attention. A number of studies have been carried out on carbon monoxide exposure under certain conditions, for example when using candles, gas stoves or in waterpipe cafés. In addition, the World Health Organization has derived guideline values for different exposure times. Due to its molecular properties, carbon monoxide is very suitable for selective and sensitive measurement with high time resolution using infrared techniques. In addition, sensor technology has made significant progress, so that robust devices are now available for online monitoring. Carbon monoxide can definitely be considered a priority pollutant for indoor air. Actually, increased concentrations are always associated with health risk. It is therefore recommended to use carbon monoxide as an indicator of indoor air quality. This can be realized in a variety of ways and preferably in combination with other parameters.

The composition of air-exposed surfaces can have a strong impact on air quality and chemical exposure in the indoor environment. Third hand smoke (THS), which includes surface-deposited cigarette smoke residue along with the collection of gases evolved from such residues, is becoming increasingly recognized as an important source of long-term tobacco smoke exposure. While studies have described gas/surface partitioning behaviour and some multiphase reaction systems involving THS, the possibility of time-dependent changes in chemical composition due to chemical reactivity that is endogenous to the deposited film has yet to be investigated. In this study, sidestream cigarette smoke was allowed to deposit on glass surfaces that were either clean or pre-coated with chemicals that may be oxidized by reactive oxygen species found in the smoke. Surface films included a low volatility antioxidant, tris(2-carboxyethyl)phosphine (TCEP), and two compounds relevant to surface films found within buildings, oleic acid (OA) and squalene (SQ). Upon deposition, oxidation products of nicotine, TCEP, OA, and SQ were formed over time periods of hours to weeks. The inherent oxidative potential of cigarette smoke deposited as a THS film can therefore initiate and sustain oxidation chemistry, transforming the chemical composition of surface films over long periods of time after initial smoke deposition. An interpretation of the THS oxidation results is provided in the context of other types of deposited particulate air pollutants with known oxidative potential that may be introduced to indoor environments. Continued study of THS and deposited surface films found indoors should consider the concept that chemical reservoirs found on surfaces may be reactive, that the chemical composition of indoor surface films may be time-dependent, and that the deposition of aerosol particles can act as a mechanism to initiate oxidation in surface films.

Increased throughput and container ship backlogs at the ports of Los Angeles and Long Beach due to supply chain disruptions related to the COVID-19 pandemic caused a significant increase in the number of ships near the California coast, leading to concerns about increased air pollution exposure of nearby communities. We use a combination of satellite-based observations from TROPOMI and ground-based observations from routine surface monitoring sites with chemical transport model results to analyze the changes in NO₂ and PM_2.5 in the Los Angeles Basin during a period in 2021 when the number of ships was at its peak. Using simulations to account for meteorological effects, changes are apportioned to emissions and meteorology. The largest emission-related changes in column NO₂ occurred immediately east of the ports where emission-related NO₂ increased by 28% compared to the baseline (2018–2019 average). In Central Los Angeles, emission reductions led to a 10% decrease in NO₂ during the same period. Emission-related PM_2.5 increased by 0.7 μg m⁻³ on average with a maximum increase of 4.5 μg m⁻³ in the eastern part of Basin. The emission/meteorology attribution method presented here provides a novel approach to quantify emission-influenced changes in air quality that are consistent with observations and suggests that both NO₂ and PM_2.5 were elevated in parts of the Los Angeles area during a period of increased port activity.