Environmental science: atmospheres最新文献

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.

Atmospheric oxidation of ammonia is initiated by its reaction with the hydroxyl radical, producing the aminyl radical (NH₂). Thus far, it has been believed that the subsequent fate of NH₂ is to react bimolecularly with other atmospheric trace gases like NO, NO₂, or O₃. Its reaction with O₂ has been considered insignificant under atmospheric conditions. However, this is based on a rate coefficient that is orders of magnitude smaller than those known for analogous reactions of O₂ with carbon-, sulfur-, and other nitrogen-centered radicals. We demonstrate by multireference calculations and kinetic modelling that the reaction of NH₂ and O₂ leading to the formation of the aminoperoxyl radical (NH₂O₂) occurs with a rate coefficient similar to those of the aforementioned analogous radicals. We show that the previously estimated small rate coefficient is due to an unimolecular rate limiting step in the formation of measured products rather than the initial NH₂ + O₂ reaction. The lack of experimental detection of NH₂O₂ in the existing literature is likely due to the experiments being conducted at either high temperature or low pressure. We show that the atmospheric presence of NH₂O₂ depends greatly on atmospheric conditions. Its formation is an important, yet previously overlooked pathway in atmospheric ammonia oxidation, especially at low temperatures.

Settled road dust is a sink for polycyclic aromatic hydrocarbons (PAHs), which have hazardous effects on ecosystems. Sampled dust from the solid surfaces of Awka, Ekwulobia, and Rumuodomaya-Ogale, Eastern Nigeria, was collected between December 2019 and March 2020, sieved to obtain uniform particle size, subjected to solvent extraction, and subsequently purified using silica gel/Na₂SO₄ column. The extracts were analyzed using gas chromatography coupled with a flame ionization detector (GC-FID), and the measured PAH concentrations followed the decreasing order: Rumuodomaya-Ogale > Ekwulobia > Awka. Dusts from the Eze-Uzu junction, Ekwulobia roundabout axis, Victoria hospital premises, Eleme junction, and Elelenwo-Akpajo bypass had total PAH concentrations (μg g⁻¹) that ranged from 0.480–0.613, 0.672–0.926, 0.739–1.388, 1.497–7.915, and 1.423–7.037, respectively. The concentration of benzo(a)pyrene equivalent (BaPE) (μg g⁻¹) in dust samples varied across locations as follows: Eze-Uzu junction (0.0047–0.0690), Government house (0.0047–0.0689), Ekwulobia roundabout (0.0720–0.1942), Victoria hospital premises (0.0720–0.2291), Eleme junction (0.2570–1.4930), and Elelenwo-Akpajo bypass (0.2455–1.3934). Benzo(a)pyrene total toxicity equivalence (BaP-TEQ) values in dust of all the sampled locations indicated no cancer risk (CR) to residents, with benzo(a)pyrene as the main contributor. In all cases, CRing values were higher in children than in adults. PAHs in dust indicate contamination via vehicular emissions, waste burning, and incomplete diesel or gasoline combustion. The point source of PAH in the study areas—open waste burning and the explosion of diesel-laden vehicles—should be regulated.

In this paper, we investigate physico-chemical properties of particulate matter (PM) at an urban mixed site (UB) and two roadside (RS) sites during the 2015 Metro Manila Aerosol Characterization Experiment (MACE). Aerosol particle number size distributions (0.01–10 μm diameter) were measured using a combination of a mobility particle size spectrometer and aerodynamic particle size spectrometers. PM_2.5 filter samples were analyzed for total mass, organic carbon (OC), elemental carbon (EC), water-soluble inorganic ions, and elemental species. Mass closure between the gravimetric mass, chemical composition, and mass concentration derived from the number size distribution was performed. We found that the bulk PM_2.5 mass was dominated by carbonaceous materials, followed by secondary inorganic aerosols and crustal matter at all sites. The average OC/EC ratios at the RS sites (0.16–1.15) suggest that a major fraction of the aerosol mass at these sites derives from traffic sources, while the OC/EC ratio at the UB site (2.92) is indicative of a more aged aerosol, consistent with greater contribution from secondary organic carbon (SOC) formation. The ultrafine particles (UFPs, diameter < 100 nm) dominated (89–95%) the total particle number concentration at the three sites, highlighting the importance of such measurements in this region. However, UFPs have low mass contribution to PM_2.5 (7–18%), while particles in the accumulation mode (diameter 100–1000 nm) accounted for most of the number-derived PM_2.5 mass concentration (61–67%). On average, strong agreement between the chemically-derived mass and the gravimetric mass was found (slope = 1.02; r² = 0.94). The number-derived mass concentration correlated well with the gravimetric PM_2.5 mass (slope = 1.06; r² = 0.81). These results highlight the need for more comprehensive PM characterization, particularly focusing on size-resolved chemical composition and particle number size distributions. The mass closure approach presented in this work provides a framework for a conversion between number size distributions and PM_2.5 mass concentration in real time in an environment with similar characteristics.

Organic aerosol (OA) has a significant impact on Earth's climate and human health, while its chemical composition remains largely unknown. A detailed analysis of the chemical composition of particulate matter (PM) can identify origins, sources and transformation pathways and reveal mitigation potential for the anthropogenic organic fraction. Here, we follow a top-down molecular resolution approach of source attribution of organic compounds in PM_2.5 at a rural background station in central Europe. One year of PM filters were measured using ultra-high-performance liquid chromatography coupled to electrospray ionisation high-resolution Orbitrap mass spectrometry. Non-target analysis detected over 6000 compounds, which hierarchical cluster analysis separated into a biogenic and an anthropogenic compound cluster. Compounds of the biogenic cluster make up a large part of SOA during summer, indicating strong local influence by the vegetation. Anthropogenic compounds are relatively enriched during colder conditions, with temporarily strong transport of air pollution. Concentration-weighted trajectories show the air mass origins of these pollution events and allow for an interpretation of potential sources.

Black carbon (BC) is a significant environmental health and climate forcing concern. Direct measurement of BC fluxes using eddy covariance can quantify emissions and identify sources. Previous studies have examined urban BC emissions in highly polluted countries such as China and India, but to date no equivalent research has been done in the UK and Europe. Here, we present black carbon flux data from a single particle soot photometer (SP2) deployed in an eddy covariance system at the BT (formerly British Telecommunications) Tower in central London. Mean BC mass (number) fluxes with a size range of 60 nm to 600 nm were 6.83 ng m⁻² s⁻¹ (443 cm⁻² s⁻¹) in summer and 13.3 ng m⁻² s⁻¹ (687 cm⁻² s⁻¹) in winter, indicating relatively low BC emission when compared to Delhi, which is likely due to the introduction of the ultra-low emission zone (ULEZ) and requirements for road diesel vehicles to meet Euro 6 standards or higher. However, flux footprint analysis identified strong point sources near construction sites during winter and summer observations, which implies that non-road mobile machinery (NRMM) emissions can dominate over traffic BC emissions. This implies that tightened NRMM regulations can help future air quality in London. Observations indicate that the UK's National Atmospheric Emissions Inventory (NAEI) overestimates BC emissions by a factor of 5, although large uncertainties are expected for the combustion sector in the manufacturing industry. The estimate of traffic emissions is more accurate.