Environmental science: atmospheres最新文献

Oxidation of emitted anthropogenic and biogenic volatile organic compounds (VOCs) and subsequent chemical reactions reduce the volatility of the products formed leading to secondary organic aerosol (SOA) formation. Despite the huge diversity of individual SOA compounds, SOA modelling is often simplified and estimated at the initial oxidation step neglecting chemical and physical process influencing SOA formation e.g. advection, deposition, chemical degradation and aging processes. To overcome this shortcoming, the chemical gas-phase mechanism URMELL was developed. URMELL treats more than 40 distinct oxidised gas-phase SOA (gasSOA) precursors with individual molecular characteristics and physico-chemical partitioning properties enabling a much more explicit gasSOA treatment for products of aromatics and isoprene oxidation. In this study, CTM simulations using COSMO-MUSCAT were performed with URMELL and compared with a simplified gasSOA scheme applying the widely used gas-phase mechanism RACM. The comparison indicates a delayed and thereby locally shifted gasSOA formation when applying URMELL. This effect is caused by the formation of multigenerational and multifunctional products along the transport trajectory whereby accounting for changes in the oxidant regime and leading to a multitude of gasSOA substances with URMELL. For isoprene and aromatics, URMELL simulates higher contributions of products with lower volatilities whereby aromatics generate even non-volatile products which can partition in new particle formation. The non-volatile aromatic products increase the average aromatic surface gasSOA concentration (30% on 20^th of May 2014) and show unexpectedly high concentrations in remote spruce forest areas, away from the emission sources, highlighting the potential of the detailed schemes and its need for application in CTMs.

Mt. Etna, an open-vent, persistently degassing volcano, is the tallest and most active volcano in Europe. Aerosols from the summit (Bocca Nuova crater), downwind (about 10 km from the crater) and control sites were collected during the EUROVOLC EPL-REFLECT field campaign in July 2019 and analysed for aerosol mass determination, major inorganic and organic ions, and soluble and insoluble metals. Computational modelling (using the models E-AIM, ISORROPIA, and Visual MINTEQ) was performed to determine the speciation of metal ions in the deliquescent aerosol phase within the volcanic plume and in aerosol collected in the town of Milo (Catania, Italy), a few km downwind of Mt. Etna and influenced by transport of the volcanic plume. The aerosol liquid water concentration at the summit was strongly dependent on the determination method – with ISORROPIA calculating a water concentration a factor of 10² lower than that of E-AIM, which itself was a factor of 10²–10³ lower than the total water content of the plume measured by infrared spectroscopy. The calculated pH was predominantly acidic (except for ISORROPIA calculations in the three samples), with the highest acidity observed where the water concentration was the lowest. Only a few metals were shown to have significant organic–ligand complexation in the aerosol, i.e., Al(III), Cu(II), and Fe(III) with oxalate, in the deliquescent aerosol within the plume. When considering the total amount of water of the plume, lower complexation was observed because of more diluted species concentration and less acidity.

The influence of biomass burning (BB)-derived organic aerosol (OA) emissions on solar radiation via absorption and scattering is related to their physicochemical properties and can change upon atmospheric aging. We systematically examined the compositionally-resolved mass concentration and production of primary and secondary organic aerosol (POA and SOA, respectively) in the NC A&T University smog chamber facility. Mass spectral profiles of OA measured by the Aerosol Chemical Speciation Monitor (ACSM) revealed the influence of dark- and photo-aging, fuel type, and relative humidity. Unit mass resolution (UMR) mapping, the ratio of the fraction of the OA mass spectrum signal at m/z 55 and 57 (f₅₅/f₅₇) vs. the same fraction at m/z 60 (f₆₀) was used to identify source-specific emission profiles. Furthermore, Positive Matrix Factorization (PMF) analysis was conducted using OA mass spectra, identifying four distinct factors: low-volatility oxygenated OA (LV-OOA), primary biomass-burning OA (BBOA), BB secondary OA (BBSOA), and semi-volatile oxygenated OA (SV-OOA). Data supports a robust four-factor solution, providing insights into the chemical transformations under different experimental conditions, including dark- and photo-aged, humidified, and dark oxidation with NO₃ radicals. This work presents the first such laboratory study of African-derived BBOA particles, addressing a gap in global atmospheric chemistry research.

Industries, governments, and regulators need trustworthy emissions data to enable them to make informed decisions regarding methane abatement strategy and policies. There are many differing data reporting metrics, as well as a diverse range of both emission sources and methods for monitoring emissions. Different data structures and terminologies can be used to describe similar objects, activities, or characteristics associated with methane monitoring. There is no currently accepted definition of what constitutes a methane monitoring method. Since there is no common basis to describe this information, confusion concerning language, definitions, and terminology can arise which can undermine confidence in data. This paper describes a framework, based on a set of taxonomies and a common lexicon, which aims to address these issues by providing a common structure in which data requirements, emission sources and monitoring methods can be described. The principles of metrology and quality assurance are embedded into this framework along with a means to define the temporal and spatial scales of the reporting and monitoring. It is envisaged that this framework will be developed into a standard to help facilitate more reliable transfer of information between stakeholders internationally. Usage examples for this framework include: to aid the development of test standards (between test laboratories, site operators, and standards bodies); to help ensure the most cost-effective monitoring methods are deployed for a specific purpose; to help identify technological and methodological gaps between what monitoring is needed and what is available, or to help drive more focused innovation in this field.

Co-condensation of nitric acid and ammonia vapors to form ammonium nitrate transforms from a fully semi-volatile behavior when it is relatively warm (273 K and above, typical of the seasonal planetary boundary layer) into effectively non-volatile and irreversible uptake for the limiting vapor when it is cold (well below 273 K, typical of the upper troposphere and occasionally the wintertime boundary layer). This causes the system to switch in character from the one governed by semi-volatile equilibrium (how it is usually portrayed) to the one governed by irreversible reactive uptake to even the smallest particles. Uptake involves an activation diameter, which can be as small as 1 nm for typical vapor concentrations, and subsequent growth rates can be very high, exceeding 1000 nm h⁻¹. In addition to this somewhat surprising behavior, the system provides an exemplary case for semi-volatile reactive uptake within the context of volatility and saturation ratios.

Microplastics (MPs) are defined as emerging contaminants, named so for the potential danger they pose to public health and the economy. MPs, defined as plastic particles smaller than 5 mm in size, have become significant pollutants, leading to extensive research and regulatory action. Various characterization techniques are discussed, such as FTIR, SEM-EDS, Raman, BET, DSC, XRD, GC-MS, and particle size analysis. Sampling challenges include uneven distribution, lack of standardized methods, and contamination risks. Analytical limitations stem from the need for precise detection, with current methods needing help in differentiating between MPs and other particles. Regulatory frameworks in Asian nations vary; some have comprehensive policies, while others face economic and infrastructural barriers. Researchers face critical challenges in controlling MP contamination in outdoor (OD) and indoor (ID) air. This review examines the current knowledge of the obstacles in sampling and analyzing MPs and an outline of the regulations in different Asian countries with different characterization methods to analyze the MPs. Furthermore, this review emphasizes the importance of unified protocols and strong regulations to improve data comparability and encourage collaborative efforts. By shedding light on the complexities of MP research and regulation in Asia, this paper aims to promote a better understanding and advocate for collective action to address these challenges and safeguard ecosystems.

The reaction of gas-phase SO₂ with unsaturated carbon–carbon double bonds forms organosulfates at the surface of the aerosol. Previous studies have focused on the reaction products and not the fate of organic films in the atmosphere. Neutron reflectometry was used to study the interaction of gas-phase SO₂ at the air–water interface with organic material extracted from atmospheric particulate matter and pure proxy chemicals to determine whether the reaction of organic films with SO₂ removes the film and if a product film is formed. Films formed from atmospheric aerosol collected in urban and woodland environments typically produced a layer of approximately 0.6 nm thickness, whereas a thick (>40 nm) film was formed by the woodsmoke sample. Fitting of this thicker woodsmoke film suggested a three-layered structure at the interface that has been interpreted to be consistent with a surfactant-rich layer next to the air–water interface, a mid-layer rich in polyaromatic hydrocarbons (PAH), and topped with a more aliphatic region. The multilayer structure of atmospheric extracted material at the air–water interface is potentially an exciting result that requires further study. Gas-phase SO₂ was confirmed to react with pure insoluble surfactant molecules at the air–water interface that contained carbon–carbon double bonds (oleic acid) and did not react with a similar saturated surfactant (stearic acid). No reaction was observed during the interaction of SO₂ and atmospheric material extracted from urban and woodland environments, and no material appeared to be removed from the interface; however, films made from woodsmoke-extracted material did appear to be altered by SO₂ but there was no significant loss of material. In addition, the gas-phase ozone mixing ratios in the neutron blockhouse, which have historically been of some concern for reactions with organics, were found to be of the order 15 ppb, with no evidence of additional production in the neutron beam-path. Owing to a lack of substantial removal of material from real atmospheric extracted films, SO₂ is not considered atmospherically significant for the removal of organic films from the air–water interface.

Nitrate ion-based chemical ionization mass spectrometry (NO₃⁻-CIMS) is widely used for detection of highly oxygenated organic molecules (HOMs). HOMs are known to participate in molecular clustering and new particle formation and growth, and hence understanding the formation pathways and amounts of these compounds in the atmosphere is essential. However, the absence of analytical standards prevents robust quantification of HOM concentrations. In addition, nitrate-based ionization is usually very selective towards the most oxygenated molecules and blind to less oxygenated compounds hindering the investigation of molecular formation pathways. Here, we explore varying concentrations of nitric acid reagent gas in the sheath flow of a chemical ionization inlet as a method for detecting a wider range of oxidation products in laboratory-simulated oxidation of benzene and naphthalene. When the concentration of reagent nitric acid is reduced, we observe an increase in signals of many oxidation products for both precursors suggesting that they are not detected at the collision limit. The sensitivity of naphthalene oxidation products is enhanced to a larger extent than that of benzene products. This enhancement in sensitivity has a negative relationship with molecular oxygen content, the oxygen-to-carbon ratio, the oxidation state of carbon, and lowered volatility. In addition, the sensitivity enhancement is lower for species that contain more exchangeable H-atoms, particularly for accretion products. While more experimental investigations are needed for providing the relationship between enhancement ratios and instrumental sensitivities, we suggest this method as a tool for routine check of collision-limited sensitivities and enhanced detection of lower-oxygenated species.

In this study, aqueous sodium thiosulfate microdroplets mixed with glucose or sucrose are used as a model system of ternary inorganic–organic aerosols. The interfacial ozone oxidation of thiosulfate, which has been characterized in our previous work [J. Phys. Chem. C, 2023, 127, 6248], is exploited via aerosol optical tweezers to determine the bulk diffusivity of thiosulfate in such inorganic–organic microdroplets under variable conditions of RH and inorganic–organic mass ratio. A kinetic multilayer model of aerosol surface and bulk chemistry (KM-SUB) is also utilized to retrieve the bulk diffusivity of thiosulfate from the kinetics measurement results. The kinetics results at relatively high RHs show that the observed reaction time scale increases when lowering RH, and the magnitude of thiosulfate diffusion coefficients is between Stokes–Einstein predictions for binary sodium thiosulfate–water systems and binary organic–water systems, indicating the dominant diffusion kinetics of thiosulfate in viscous fluid matrices of homogeneously mixed inorganics and organics. However, when RH is below 30% for glucose or 40% for sucrose, the kinetics results exhibit incomplete thiosulfate depletion upon prolonged ozone exposure, indicating the co-existence of two distinctly fast and slow diffusion components of thiosulfate. The diffusion coefficients of undepleted thiosulfates become similar to the SE predictions of binary organic–water systems, and they are a few orders of magnitude smaller than those of rapidly depleted thiosulfates. According to the literature, such a diffusion limitation may be attributed to an ion–molecule effect which may lead to the formation of inorganic–organic microgels in aerosols at atmospherically relevant RHs. The results of this work suggest that the cooperative effects of inorganics and organics can play a potential role in the reaction kinetics of atmospheric inorganic–organic aerosols.

Semivolatile organic compounds (SVOCs) in exhaust gas, though not directly regulated by emission standards, play a crucial role in assessing both conventional and alternative fuels. Our aim is to compare the differences in and toxicological effects of SVOC exhaust emissions from conventional and alternative fuels under sub-freezing conditions. High levels of NO_x, CO₂ and PAHs in SVOCs were observed in DI-E2 (EN590 winter-grade diesel), with E10 (gasoline with 10% ethanol) exhibiting higher CO₂ and PAH levels compared to E85 (high-blend ethanol with an 83/17% ethanol–gasoline ratio). SVOCs from DI-E6 (EN590 diesel) demonstrated significant cytotoxicity, while E10 resulted in higher inflammatory mediators and genotoxicity. Our findings show that SVOC composition and toxicity in exhaust gas differ based on the fuel type. Despite new emissions regulations reducing diesel vehicle emissions, SVOC toxicity remains unchanged. Toxicity from SVOCs in compressed natural gas and ethanol/gasoline vehicles is notable, with gasoline exhaust showing high inflammatory and genotoxic potential.