Environmental science: atmospheres最新文献

The enforcement of global fuel sulfur content (FSC) regulations has significantly reduced SO₂ and particulate matter (PM) emissions from ships. However, the impact of the International Maritime Organization's (IMO) sulfur reduction policy on gaseous hydrocarbon emissions, including volatile and intermediate volatility organic compounds (VOCs/IVOCs), remains underexplored. In this study, a 4-stroke single cylinder marine engine was operated using marine gas oil (MGO, FSC = 0.01%) and low-sulfur heavy fuel oil (LS-HFO, FSC = 0.5%) across various engine loads, ranging from 20 kW to a maximum of 80 kW. Emissions were photochemically aged in the oxidation flow reactor “PEAR,” simulating an equivalent photochemical aging period from 1.4 ± 0.2 to 4.6 ± 0.8 days related to the OH· exposure. Emission factors (EFs) of all targeted VOCs/IVOCs varied significantly, ranging from 20.0 ± 2.5 to 180 ± 20 mg kWh⁻¹ and from 26.0 ± 11.0 to 280 ± 100 mg kWh⁻¹ from a high (80 kW) to low engine load (20 kW) for MGO and LS-HFO, respectively. Monoaromatics dominated total fresh emissions for MGO (64%) and LS-HFO (76%), followed by alkanes. Naphthalene and alkylated naphthalene content declined more than monoaromatic and alkane content, thus changing the VOC/IVOC emission pattern after photochemical aging. Estimated SOA from targeted VOC/IVOC precursors accounted for 41% of the measured secondary organic aerosol (SOA) for MGO, while a lower contribution (34%) was observed for LS-HFO at 20 kW engine load, highlighting the role of unmeasured VOCs/IVOCs in SOA formation. Expanding the research on the effects of atmospheric aging on marine emissions will offer valuable insights into this underexplored area.

Stratospheric aerosol injection (SAI) has been proposed as a geoengineering approach to temporarily offset global warming by increasing Earth's albedo. Here, we utilize light scattering calculations to examine how introducing solid aerosol particles into the stratosphere can enhance the Bond albedo, a key metric linking reflectivity directly to radiative forcing. We explore how particle size, refractive index (both real and imaginary components), and morphology (core–shell configurations) affect single scattering albedo, phase function, and the resulting integrated solar reflectivity. Our results show how the optimal aerosol size is governed by matching the wavelength of dipolar resonances with the peak of incoming solar spectral irradiance. We also examine how dispersion, absorption, and size distribution affect the extent of the Bond albedo enhancement and radiative forcing. Coated particles are also studied, and we find that very thin lower-index coatings can spoil albedo enhancement (e.g., layers of water or sulfuric acid that are only a few nanometres thick). Conversely, designing core–shell particles with a thin, higher-index shell and a low-density core can retain high reflectivity while substantially reducing particle mass and settling velocity, potentially extending the stratospheric residence time. The framework discussed here is versatile, readily extending to systems beyond homogeneous spherical particles, and it provides a straightforward means of comparing candidate SAI materials while guiding future laboratory studies, work on particle design, field experiments, and climate model parameterizations to assess the viability and risks of stratospheric aerosol geoengineering.

Wildfires impact global climate and public health by releasing gases and aerosols. Phthalic anhydride, a toxic chemical detected in wildfire smoke, has been primarily linked to the daytime oxidation of naphthalene and methylnaphthalenes. The recent report of phthalic anhydride in the nighttime oxidation of furan and furfural suggests that other heterocyclic volatile organic compounds (VOCs) may also act as potential precursors of phthalic anhydride through previously unrecognized pathways. This study presents the production of phthalic anhydride derived from the nighttime chemistry of 2-methylfuran, thiophenes, and methylpyrroles, with its mass fraction comprising ∼0.1–0.4% of the secondary organic aerosols (SOAs) derived from these heterocyclic VOCs. Phthalic anhydride is proposed to be produced via the cycloaddition of heterocyclic backbones. We estimate that the nighttime oxidation of heterocyclic VOCs may contribute variably to phthalic anhydride production across different fuel types, with a ∼30% contribution during wiregrass combustion. Overall, our findings highlight the need to further investigate the production of phthalic anhydride from these previously unrecognized precursors and pathways in wildfire smoke to better understand their atmospheric implications.

We present a “diagonal” Volatility Basis Set (dVBS) comparing gas-phase concentrations of oxygenated organic molecules (OOM) to their condensed-phase mass fractions. This permits closure of vapor concentrations with particle composition constrained by particle growth rates, allowing the contributions of quasi non-volatile condensation, equilibrium partitioning, and reactive uptake to be separated. The dVBS accommodates both equilibrium and dynamical (growth) conditions. Growth implies an association between gas and particle concentrations governed by a “condensation line” that is set by the particle growth rate, which fixes the total (excess) concentration of condensible vapors. The condensation line defines an infeasible region of high particle mass fraction and low gas concentration; under steady-state growth conditions, compounds cannot appear in this infeasible region without being formed by condensed-phase chemistry. We test the dVBS with observations from the CLOUD experiment at CERN using data from a FIGAERO I⁻ Chemical Ionization Mass Spectrometer measuring vapors directly and particle composition via temperature programmed desorption from a filter. A dVBS analysis finds that data from an α-pinene + O₃ run at 243 K are consistent with volatility driven condensation forming the large majority of particle mass, with no compounds clearly within the infeasible region.

The impact of poor air quality (AQ) on public health has long been recognised and considerable efforts have been made to improve it across the UK. The UK has a far reaching AQ monitoring network and this study summarises the evolution of UK AQ over the period 2015–2024, focusing on the pollutants NO₂, O₃ and PM_2.5 and exploring their drivers. Concentrations of NO₂ and PM_2.5 exhibit robust negative trends across the whole country while concentrations of O₃ increase. Comparing 2015–2016 to 2023–2024, the median number of days per year for which DEFRA AQ sites breached the WHO 2021 target decreased from 136 to 40 (−70%) for NO₂ and from 60 to 22 (−63%) for PM_2.5. This trend was mirrored in other AQ monitoring networks and highlights that, while progress is being made, acceptable levels of AQ are yet to be reached. Over the same period, median O₃ exceedances increased from 7 to 14 days per year. Nationwide analysis of diurnal variation in the pollutants and the use of airmass back trajectory clustering and statistical modelling for three locations – Reading, Sheffield and Glasgow – suggests that local traffic plays a dominant role in NO₂ pollution, PM_2.5 is influenced more by long range transport and O₃ increases are being driven in part by decreases in NO₂. From an AQ policy perspective, this suggests continued focus on traffic emissions will reduce NO₂, (inter)national rather than local efforts are most critical for PM_2.5 improvements, and reductions to VOC emissions must accompany NO₂ if further O₃ increases are to be avoided.

Atmospheric ice nucleating particles (INPs) can affect cloud radiative properties and lifetimes and thus Earth's climate. Such particles may be emitted into the atmosphere from seawater via wave breaking processes. Here, we perform an exploratory investigation on the ice nucleating properties of seawater sampled on four days over a year (February, April, June, and November) from a coastal site near Aarhus in Denmark. We use a cold stage instrument (droplet size: 1 μL) to probe immersion mode freezing events. We find that bulk seawater contains INPs with T₅₀ values around −20 °C independent of the month of sampling and INP concentrations ranging from 6 × 10³ to 5 × 10⁶ INP L⁻¹ in a temperature range of −12 to −34 °C across all four samples. All samples displayed sensitivity to filtration (0.02 μm), as indicated by a decrease in INP concentration (lowering of freezing temperature). The filtered April and June samples froze at higher temperatures than the filtered November and February samples, which could indicate a variation in the population of INPs (>0.02 μm) over the year. Sea surface microlayer samples did not show enrichment of INPs compared to bulk seawater. Our results are discussed in the context of INP activity of seawater from other locations. While further studies are needed to understand the nature and potential seasonality of seawater INPs, we confirm the presence of INPs in coastal Baltic seawater that may contribute to atmospheric INP concentrations.

In this study, we combine aerosol observations with high-resolution Eulerian (WRF-CHIMERE) and Lagrangian (FLEXPART) modelling to investigate the source regions, emission sources, transport pathways, and chemical transformation of sulphate aerosols at the high-altitude Monte Cimone station during July 2017. Our analysis shows that marine air masses are linked to higher levels of sulphate at Monte Cimone. In particular, the sea plays a dominant role in enhancing the oxidation of sulphur dioxide (SO₂) into sulphate due to prolonged exposure to elevated hydroxyl radical (OH) concentrations over the sea. At the same time, sensitivity simulations reveal that industrial emissions contribute significantly to sulphate levels at Monte Cimone, even when air masses have spent a long time travelling over the sea. Furthermore, examination of vertical atmospheric dynamics indicates that free tropospheric air masses favour higher concentrations of sulphuric acid likely due to lower condensation sink (CS) conditions in the free troposphere (FT). In contrast, boundary layer conditions were found to enhance the transport of dimethyl sulphide (DMS) oxidation products, meaning that, over the Mediterranean Sea, DMS and its oxidation products do not reach the FT efficiently. Our results highlight the complex interaction between marine and terrestrial sources, atmospheric chemistry, and transport mechanisms in shaping sulphate aerosol levels at high-altitude sites. They also provide valuable insights into sulphate sources and transport processes over large geographical areas.

The chemistry of organic peroxy radicals (RO₂) is crucial for ozone and secondary organic aerosol formation in the troposphere. The level of nitrogen monoxide (NO) exerts a major control on further reactions of peroxy radicals. The research on these reactions in the absence of NO has been receiving increasing attention recently. The current studies under these conditions, typically associated with pristine environments, are focused on understanding the formation of highly oxygenated organic molecules (HOMs) via autoxidation and generation of accretion products, which supposedly result from peroxy radical permutation reactions (RO₂ + RO₂). Apart from the potential OH production from some oxygenated peroxy radicals, there is less research activity on the reactions of peroxy radicals with HO₂. This article reviews the existing literature data available on RO₂ + HO₂ reactions and highlights the gaps where future research is required. To date, limited information has been provided on the reactions of HO₂ with functionalized RO₂, particularly for β-hydroxyalkyl peroxy radicals, carbonyl-substituted peroxy radicals other than acyl peroxy, and peroxy radicals containing at least two functionalities. In addition, the temperature dependence of product branching ratios is not well established. Future studies targeting the influence of RO₂ + HO₂ on the tropospheric HO_x (OH + HO₂) budget should ideally enlarge the dataset of OH yields from various peroxy radical structures. This also highlights the need to broaden the investigations on the formed hydroperoxides, whose gas-phase chemistry is not well known.

Environmental contamination in Ghana, driven by dust deposition, particulate matter (PM), reactive nitrogen, sulfur, and heavy metals, poses significant risk to public health and the environment. However, comprehensive assessments of the spatial distribution and seasonal variations of these pollutants remain limited. To address this gap, this study synthesizes data from 68 site-specific studies conducted between 1997 and 2024. Our findings reveal substantial regional disparities in contamination levels. During the Harmattan season, the Northern region accounted for 52% of total dust deposition, while the Central and Southern regions contributed 12% and 37%, respectively. The Central region exhibited the highest concentrations of PM, with median values of PM2.5 (489 μg m⁻³), PM10 (703.5 μg m⁻³), and TSP (710.5 μg m⁻³). Heavy metal contamination in agricultural products was particularly concerning, with cocoa showing elevated levels of copper (48.67 mg kg⁻¹), lead (70.03 mg kg⁻¹), and iron (41.60 mg kg⁻¹). Fish samples revealed high lead (5.97 mg kg⁻¹) and iron (156.39 mg kg⁻¹). Lettuce and onions demonstrated moderate contamination with lead and cadmium. In mining regions such as Obuasi, lead and arsenic concentrations exceeded WHO safety limits. Sulfur deposition was notably high in Southern Ghana, constituting 81.4% of airborne pollutants. Rainwater contamination, primarily from sulfate, contributed to acidic rainfall (pH < 6.5) in the Southern and Central regions. These findings underscore the urgent need for targeted interventions, particularly in mining and urban areas. Implementing stronger pollution control measures, enhancing monitoring systems, and developing specific strategies to mitigate risks to public health and agriculture are critical steps toward addressing these environmental challenges.

Landscape fires in subtropical southern Africa (2-20°S) are a prominent regional source of nitrogen oxides (NO _x ) and ammonia (NH₃), affecting climate and air quality as precursors of tropospheric ozone and aerosols. Here we evaluate GEOS-Chem model skill at reproducing satellite observations of vertical column densities of NO₂ from TROPOMI and NH₃ from IASI driven with three distinct and widely used biomass burning inventories (FINNv2.5, GFEDv4s, GFASv1.2). We identify that GFASv1.2 use of fire radiative power and a NO _x emission factor that is almost half that used by the other two inventories is most consistent with TROPOMI and that FINNv2.5 use of active fires and landscape-specific fuel loads and biomass consumed is most consistent with IASI. We use a simple mass-balance inversion to calculate top-down NO _x emissions of 1.9 ± 0.6 Tg NO for June-October and NH₃ emissions of 1.2 ± 0.4 Tg for July-October. All inventories collocate NO _x and NH₃ emissions, whereas most of the pronounced emissions of NO _x and NH₃ are separate and have distinct seasonality in the top-down estimate. We infer with GEOS-Chem more efficient ozone production (13 Tg ozone per Tg NO) with the top-down informed NO _x emissions than the inventory emissions, as GFASv1.2 NO _x is almost 20% less than top-down NO _x and the 2.3- to 2.5-times greater FINNv2.5 and GFEDv4s NO _x reduces sensitivity of ozone formation to NO _x . Both NO _x and NH₃ top-down emissions are unaffected by use of plume injection heights, limited to GFASv1.2 in GEOS-Chem, and NH₃ is insensitive to acidic sulfate and nitrate aerosol emissions absent in all inventories. The top-down emissions estimates and comparison to satellite observations suggest a hybrid bottom-up approach could be adopted to discern byproducts of smouldering and flaming fires.