Environmental science: atmospheres最新文献

Structure–activity relationships (SARs) are essential components of detailed chemical models, where they are employed to provide kinetic information when high-quality experimental or theoretical data are unavailable. Notwithstanding, there are very few types of SARs that are routinely employed to estimate reaction kinetics. Accordingly, a new temperature-dependent and site-specific technique for rate coefficient estimation is presented, based on the electrotopological state (E-state), a fundamental property that can describe the substituent effect upon each hydrogen environment in a molecule. This accounts for the electronic character of individual atoms within molecules and their respective distances from one another. This method is applied to the hydrogen abstraction reactions of OH with alkanes and haloalkanes, where it was found to perform well compared with other approaches for molecules whose rate coefficients have been measured experimentally over a broad temperature range (∼200–1500 K). To extend this comparison, an efficient software tool for batch-estimated rate coefficients has been developed. By applying this software to fully enumerated lists of halocarbons containing from one to four carbon atoms, we were able to compare predictions of >100 000 species between techniques, and although experimental coverage is sparse, we could assess the degree of consensus between these estimates. Disagreement between methods was found to increase with carbon number, and differences of up to three orders of magnitude were observed in some cases. The reasons for these discrepancies and possible solutions are discussed. In a further demonstration of the utility of the E-state approach, we show that it can also be used to calculate bond-dissociation energy (BDE), which also compares favourably with a state-of-the-art literature method. The E-state approach not only provides accurate predictions of rate coefficients, but it does so with fewer fitting parameters and by being constrained by a fundamental molecular property. From this we conject that it is less prone to overfitting and more easily expanded to unfamiliar substituents than previous SAR approaches. The efficiency and robustness with which estimates of BDE and rate coefficients are made over a wide range of conditions will be of relevance to a variety of fields including atmospheric and combustion chemistry.

Megafires are increasingly generating Pyrocumulus clouds (PyroCus) through the interplay of atmospheric conditions such as stability and humidity, hot updrafts, and emitted aerosols from burning vegetation. As megafires become more frequent, the annual radiative influence of PyroCus on the climate is intensifying. In this study, we aim to quantify the aerosol mass and black carbon content that PyroCus injects into the stratosphere, which can persist for 3 to 15 months. Utilizing aircraft-sampled smoke plumes from both the Northern and Southern Hemispheres, our findings indicate that the mass fraction of black carbon within PyroCus remains consistent, ranging between 0.5 and 3%. This serves as a crucial constraint for incorporating source terms in climate models. Additionally, we provide evidence of the volatile vapor 1-nonene condensing in the updrafts, which is one of likely many organic vapors contributing to increased aerosol mass concentrations. To corroborate these findings, we conducted independent Large Eddy Simulations (LES) that demonstrate organic vapor condensation can double the aerosol mass in updrafts. These resolved LES serve as a valuable guide, directing future aircraft measurement locations and further development of PyroCus mechanisms in models.

This study investigates the effects of temperature and relative humidity (RH) on the formation of secondary organic aerosol (SOA) from Δ³-carene, a prevalent monoterpene in boreal forests. Dark ozonolysis experiments of 10 ppb Δ³-carene were conducted in the Aarhus University Research on Aerosol (AURA) atmospheric simulation chamber at temperatures of 0, 10, and 20 °C. Under dry conditions (RH < 2%), the SOA formation in terms of both particle number and mass concentration shows minimal temperature dependence. This is in contrast to previous findings at higher initial concentrations and suggests an effect of VOC loading for Δ³-carene. Interestingly, the mass fraction of key oxidation products (cis-3-caric acid, cis-3-caronic acid) exhibit a temperature dependence suggesting continuous condensation at lower temperatures, while evaporation and further reactions over time become more favourable at higher temperatures. The oxygen-to-carbon ratios in the particle phase and the occurrence of highly oxygenated organic molecules (HOM) in the gas phase show modest increases with higher temperatures. Predictions from the Aerosol Dynamics and Gas- and Particle-Phase Chemistry Kinetic Multilayer Model (ADCHAM) agrees with the experimental results regarding both physical particle properties and aerosol composition considering the experimental uncertainties. At high RH (∼80%, 10 °C), a considerable increase in the particle nucleation rate and particle number concentration is observed compared to experiments under dry conditions. This is likely due to enhanced particle nucleation resulting from more stable cluster formation of water and inorganics at increased RH. However, RH does not affect the particle mass concentration.

The uncertainties over the effects of aviation non-CO₂ emissions on climate and air quality are assessed in the context of potential mitigation measures for liquid hydrocarbon fuels. Aviation non-CO₂ emissions that affect climate include nitrogen oxides (NO_x), aerosol particles (soot and sulphur-based), and water vapour. Water vapour and aerosols have small direct radiative effects but are also involved in the formation of contrails and contrail cirrus, currently, the largest non-CO₂ effect on climate. These non-CO₂ effects on climate are quantified with low confidence, compared to that of CO₂, which is quantified with high confidence. The sign of the NO_x radiative effects may change from positive to negative. The effects of soot and sulphur emissions on cloudiness are very poorly understood and studies indicate forcings that range from large negative through to small positive. NO_x and soot emissions can be reduced through changes in combustion technology but have tradeoffs with each other and CO₂. Soot can also be reduced through reduced aromatic content of fuels. In all cases, there are complex choices to be made because of tradeoffs between species, and CO₂. Contrail cirrus and soot aerosol–cloud interactions potentially have opposing signs but are both related to soot emissions (at present) and need to be considered together in mitigation strategies. Because of the uncertainties and tradeoffs involved, it is problematic to recommend definitive courses of action on aviation non-CO₂ emissions since they may be of limited effect or have unintended consequences. Aviation's non-CO₂ effects on climate are short-term, as opposed to those of CO₂, which last millennia. If aviation is to contribute towards restricting anthropogenic surface warming to 1.5 or 2 °C then reduction of emissions of CO₂ from fossil fuels remains the top priority. In terms of air quality, the situation is more straightforward with emissions standards being set by the International Civil Aviation Organization for NO_x and non-volatile particulate matter (and other minor species), which need to be complied with.

Correction for ‘Ring-opening yields and auto-oxidation rates of the resulting peroxy radicals from OH-oxidation of α-pinene and β-pinene’ by Ben H. Lee et al., Environ. Sci.: Atmos., 2023, 3, 399–407, https://doi.org/10.1039/D2EA00133K.

The primary step to minimizing air pollution effects owing to motorized vehicles in Bangladesh is to establish accurate emission modelling methods. The total yearly amount of the primary greenhouse gas, carbon dioxide (CO₂), emitted in Bangladesh up to 2020 was obtained by the World Bank. The percentage of total CO₂ emissions released from the transport sector in Bangladesh was reportedly 14.2% in 2014 and 15% in 2020; 90% of this was from on-road vehicles. So, approximately 13% of the total amount of CO₂ emissions in Bangladesh during those years found in the World Bank data can be considered to have come from its road transportation. However, Bangladesh still does not have a vehicular emission model of its own, so there is no straightforward method to quantify the harmful gases released by automobiles alone in this country as of yet. The purpose of this research is to fill this gap. This research investigated the applicability of the European emission model Computer Program to Estimate Emissions from Road Traffic Version 5.5 (COPERT 5.5) for Bangladesh. The yearly production of CO₂ from different vehicular classes in Bangladesh from 2016 to 2020 was computed using COPERT 5.5, and estimations from World Bank data were used as a benchmark. The results of this study suggest that COPERT 5.5 emission software may be applicable to Bangladesh. This research also suggested updated emission factors for CO₂ for different vehicle categories yielded by this software and developed countrywide annual vehicular emission inventories of CO₂ and 12 other major pollutants from 2016 to 2020.

Non-exhaust sources, such as brakes, tyres, roads, and clutches, emit a large portion of airborne particles in road transportation, from ultrafine to coarse sizes. While airborne wear particle emissions from brakes and road-tyre contacts have been studied extensively, emissions from clutches have been overlooked. A preliminary study using a novel test rig has indicated that dry clutches also emit airborne wear particles. This paper presents a multi-method for the assessment of ultrafine particles from dry clutches regarding the number concentration, size distribution and chemical composition. The results show that ultrafine particles are emitted both during run-in and at the steady state, featuring a bi-modal size distribution. Elementary analysis shows that the particles consist of several elements, predominately iron, silicon, and sulfur. It can be concluded from this study that ultrafine particles are always generated when the clutch is operated.

The suppression of ozone (O₃) formation due to the presence of fine particulate matter (PM_2.5) has recently been highlighted for further O₃ pollution controls in regions that suffer high ozone concentrations. Here we derive multiple PM_2.5-suppression factors for the Eastern United States (U.S.) major cities based on a non-linear fitting of the PM_2.5 and O₃ relationship from the multiyear surface observations. Our results show that these PM_2.5-suppression factors are increasing with time and generally follow the transition of the O₃-sensitive regime towards NO_x-limited chemistry. A spatial discrepancy of this suppression factor is seen currently with a higher value in the Southeastern U.S. than in the Northeastern U.S. A spatial similarity between urban regions and their downwind locations was observed for the New York City metro area. This more extensive formulation of the PM_2.5-suppression factor will further improve the ability of models to help guide O₃ and PM_2.5 concentration pollution controls.

As part of the Air Pollution and Health in Urban Environments (PASMU) project, equipment was installed in urban sites of Abidjan and Korhogo (Ivory Coast) in West Africa with the aim of monitoring the chemical composition of PM_2.5 aerosols. These installations were used to collect PM_2.5 aerosols at weekly intervals for the determination of their PM_2.5 mass, EC, OC and water-soluble ions (WSI). This database enabled us to analyse the 2 year trend (2018–2020) of the chemical composition of PM_2.5 aerosols in these two cities. In addition, this database was used to assess the sources of these aerosols using both PCA (principal component analysis) and the US Environmental Protection Agency's EPA PMF 5.0 software. The results showed that the PM_2.5 concentrations observed during the 2 dry seasons were more than twice than that during the 2 wet seasons. Also, over the 2 year study period, the observed PM_2.5 concentrations were above the WHO, 2021 standards. The analysis of the chemical composition of PM_2.5 showed that organic matter (OM) was the major fraction in the 2 cities, followed by EC in Abidjan and dust in Korhogo. Similarly, the observed trends showed greater variations in OC concentrations between the dry and wet seasons compared with EC. Also, 5 contributing sources were identified with disproportionate contributions. In Abidjan, these sources included road traffic (44.7%), domestic fires (40%), natural and road dust (11.2%), sea salt (3%), and construction dust (1.2%). In Korhogo, the sources were biomass burning and domestic fires (70.7%), road traffic (16%), road dust and sea salt (8.1%), natural dust (2.6%), and agriculture (2.5%). This study offers vital insights into identifying the primary sources of urban air pollution in West African cities. Consequently, tailored strategies based on these sources can effectively mitigate urban particulate pollution, leading to reduced emissions, enhanced air quality, and improved public health in densely populated urban regions.

Nanoplastics have been shown to be emitted into the atmosphere over land and the ocean and transported long distances to remote regions. During their atmospheric lifetime, nanoplastics may influence climate directly by absorbing and scattering sunlight and indirectly by enhancing ice or liquid cloud formation. Bare nanoplastics will not influence liquid cloud formation, since they are hydrophobic, but nanoplastics internally mixed with hygroscopic species during atmospheric aging have the potential to act as cloud condensation nuclei. Here, we report measurements of hygroscopic growth of initially 100, 200, and 250 nm polystyrene nanoplastics internally mixed with secondary organic aerosol (SOA) from the ozonolysis of α-pinene in a smog chamber. SOA formation and water uptake were quantified using parallel differential mobility analyzers at <10 and 90% relative humidity (RH), respectively. Interestingly, early in each experiment, at low SOA volumes, the mobility diameters of the humidified particles became smaller than those of the dry particles, despite certain water uptake. This discrepancy indicates that the particles at low RH have a non-spherical, partially-engulfed morphology. When they are humidified, the SOA takes up water, becomes less viscous, and coalesces around the nanoplastic, so the coated particles adopt a spherical morphology. Eventually, the SOA volume is high enough that the dry particles are also spherical, and the apparent volume of water scales linearly with the volume of SOA, as expected. A fit to measurements during this stage gives a hygroscopicity parameter of 0.02. Together, these observations have important implications on both the direct and indirect climate effects of nanoplastics in the atmosphere.