Environmental science: atmospheres最新文献

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.

The influence of a prolonged Saharan Dust event across Europe and specifically in Munich (Germany) in March 2022 was detected and analyzed in detail. The event arose from a sequence of Saharan Dust incursions intertwined with a stagnation in the regional circulation leading to the persistence of a mineral dust plume for several weeks over the region. Trace element and meteorological data were collected. Enrichment factors, size distribution analyses, and multivariate techniques such as Varimax and Self-Organizing Maps (SOM) were applied to highlight the influence of Saharan Dusts and to evaluate the pollution sources in Munich municipality. The overall results revealed how the Munich airshed was clearly affected by long-distance mineral dusts from the North African desert, that increased the concentrations of natural (e.g. Al, Mg, Ca) and anthropogenic (e.g. Sb, Mo, Pb) elements based on the different paths followed by the dusts. Moreover, the chemometric analyses revealed a range of well-defined local anthropogenic emission sources including road traffic, energy production by coal combustion (S and Se), traffic (Cu, Sb), and waste incineration (Zn).

The contributions of meteorology and emissions to air pollutant trends are critical for air quality management, but they have not been fully analyzed, especially in the background area of northern China. Here, we used a machine learning technique to quantify the impacts of meteorological conditions and emissions on PM_2.5, NO₂, SO₂, O₃, and CO pollution during 2013–2021 and evaluated their contributions to Clean Air Action policies. The annual effect of the meteorology on PM_2.5, NO₂, SO₂, and CO levels was dominated by the meteorological conditions during the cold season, while that of the O₃ level largely depended on the meteorological conditions during the warm season. Meteorology-driven anomalies contributed −14.8 to 10.3%, −8.5 to 7.3%, −11 to 7.1%, −7.9 to 6.0%, and −7.4 to 7.3% to the annual mean concentrations of PM_2.5, NO₂, SO₂, O₃, and CO during the study period, respectively. The Clean Air Actions have led to a major improvement in the air quality at regional scale, with the reduction of 1.7 μg m⁻³ year⁻¹, 0.2 μg m⁻³ year⁻¹, 1.5 μg m⁻³ year⁻¹, 0.7 μg m⁻³ year⁻¹, and 0.03 mg m⁻³ year⁻¹ for PM_2.5, NO₂, SO₂, O₃, and CO at background area, respectively, after meteorological correction. Although emissions dominated the long-term variations in pollutants, the meteorological conditions obviously played a positive role during the action periods for pollutants except for O₃. Considering the notable effects of the meteorological conditions on air pollution and the interreaction between pollutants, a more comprehensive control strategy should be considered on a broader regional scale.

Microplastics (MPs) have recently become a growing environmental pollution concern. MPs are easily transferred and ubiquitously found in ambient air. MPs in the air can act as carriers for several toxic pollutants, and exposure to MPs can lead to pulmonary diseases in humans. Polyethylene terephthalate (PET) is one of the most abundant MPs used in the manufacturing of various fibres and plastics. In this study, we present a method for the determination of mass concentrations of PET MPs in the airborne inhalable fraction of fine particulate matter (PM_2.5) using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Teflon and quartz fiber filters were tested for extraction efficiency in measuring the mass concentrations of airborne PET MPs. Teflon filters showed good recovery (80–120%) compared to quartz fiber filters. Using this method, a pilot study was carried out in Delhi, the national capital of India, and Mohali, a suburban city in the northwest Indo-Gangetic Plain (NWIGP), for the determination of mass concentrations of PET MPs present in airborne PM_2.5. The observed maximum mass concentrations of PET MPs in airborne PM_2.5 in Delhi and Mohali are 135.20 ng m⁻³ and 157.98 ng m⁻³, respectively.

The kinetics of reactions between the simplest Criegee intermediate, CH₂OO, and water vapour have been investigated at temperatures between 262 and 353 K at a total pressure of 760 Torr using laser flash photolysis of CH₂I₂–O₂–N₂–H₂O mixtures coupled with broadband time-resolved UV absorption spectroscopy. Results indicate that the reaction with water monomers represents a minor contribution to the total loss of CH₂OO under the conditions employed in this work, with an estimated rate coefficient for CH₂OO + H₂O (R1) of (9.8 ± 5.9) × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹ at 298 K and a temperature dependence described by k₁ = (3.2 ± 1.1) × 10⁻¹³ exp(−(2410 ± 270)/T) cm³ molecule⁻¹ s⁻¹. The reaction of CH₂OO with water dimers, CH₂OO + (H₂O)₂ (R2), dominates under the conditions employed in this work. The rate coefficient for R2 has been measured to be k₂ = (9.5 ± 2.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ at 298 K, with a negative temperature dependence described by k₂ = (2.85 ± 0.40) × 10⁻¹⁵ exp((2420 ± 340)/T) cm³ molecule⁻¹ s⁻¹, where rate_R2 = k₂[CH₂OO][(H₂O)₂]. For use in atmospheric models, we recommend description of the kinetics for R2 in terms of the product of the rate coefficient k₂ and the equilibrium constant K^D_eq (k_2,eff = k₂K^D_eq) for water dimer formation to allow the rate of reaction to be expressed in terms of water monomer concentration as rate_R2 = k_2,eff[CH₂OO][H₂O]² to avoid explicit calculation of dimer concentrations and impacts of differences in values of K^D_eq reported in the literature. Results from this work give k