Environmental science: atmospheres最新文献

Urban street trees can affect air pollutant concentrations by reducing ventilation rates in polluted street canyons (increasing concentrations), or by providing surface area for deposition (decreasing concentrations). This paper examines these effects in Rotterdam, the Netherlands, using mobile measurements of nitrogen dioxide (NO₂), particulate matter (PM), black carbon (BC), and ultrafine particulate matter (UFP). The effect of trees is accounted for in regulatory dispersion models (https://www.cimlk.nl) by the application of an empirically determined tree factor, dependent on the existence and density of the tree canopy, to concentrations due to traffic emissions. Here, we examine the effect of street trees on different pollutants using street-level mobile measurements in a detailed case study (repeated measurements of several neighboring streets) and a larger statistical analysis of measurements across the urban core of Rotterdam. We find that in the summertime, when trees are fully leafed-out, the major short-lived traffic-related pollutants of NO₂ and BC have higher concentrations in streets with higher traffic and greater tree cover, while PM_2.5 has slightly lower concentrations in streets with higher tree factor. UFP shows a less clear, but decreasing trend with tree factor. In low-traffic streets and in wintertime (fewer leaves on trees) measurements confirm the importance of leaves to pollutant trapping by trees, by finding no enhancement of NO₂ and BC with increasing tree cover, rather a slightly decreasing trend in pollutant concentrations with tree factor. Our observations are consistent with the dominant effect of (leafed-out) trees being to trap traffic-emitted pollutants at the surface, but that PM_2.5 in street canyons is more often added by transport from outside the street, which can be attenuated by tree cover. Overall, these measurements emphasize that both traffic-emitted and regional sources are important factors that determine air quality in Rotterdam streets, making the effect of street trees different for different pollutants and different seasons.

The proportion of ice crystals in clouds can affect cloud albedo and lifetime, impacting the Earth's radiative budget. Ice nucleating particles (INPs) lower the energy barrier of ice nucleation and thus facilitate primary ice formation in the atmosphere. Atmospheric nanoplastics (NPs) have been detected in remote regions far from emission sources, suggesting that they can become airborne and undergo long-range transport in the atmosphere. During the atmospheric residence of NPs, they could catalyse primary ice crystal formation by acting as INPs. In this study, we present results from laboratory experiments in which model NPs composed of polystyrene and polyacrylonitrile were tested for their ice-nucleating ability using the horizontal ice nucleation chamber (HINC) as a function of ice-nucleation temperature and water saturation ratio. The results showed that NPs can be effective INPs under both cirrus and cold mixed-phase cloud conditions. The surface characteristics and wettability of the NPs were analysed via scanning electron images and dynamic vapour sorption measurements, which revealed the freezing mechanism as a combination of deposition nucleation and pore condensation and freezing. The results highlight the need to enumerate and characterise NPs in the atmosphere, given their potential to get scavenged by clouds via primary ice formation in clouds.

The interface of the oceans and aqueous aerosols with air drives many important physical and chemical processes in the environment, including the uptake of CO₂ by the oceans. Transport across and reactions at the ocean-air boundary are in large part determined by the chemical composition of the interface, i.e., the first few nanometers into the ocean. The main constituents of the interface, besides water molecules, are dissolved ions and amphiphilic surfactants, which are ubiquitous in nature. We have used a combination of surface tension measurements and liquid-jet X-ray photoelectron spectroscopy to investigate model seawater solutions at realistic ocean-water ion concentrations in the absence and in the presence of model surfactants. Our investigations provide a quantitative picture of the enhancement or reduction of the concentration of ions due to the presence of charged surfactants at the interface. We have also directly determined the concentration of surfactants at the interface, which is related to the ionic strength of the solution (i.e., the "salting out" effect). Our results show that the interaction of ions and surfactants can strongly change the concentration of both classes of species at aqueous solution-air interfaces, with direct consequences for heterogeneous reactions as well as gas uptake and release at ocean-air interfaces.

Peat fires emit large quantities of particles and gases, which cause extensive haze events. Epidemiological studies have correlated wildfire smoke inhalation with increased morbidity and mortality. Despite this, uncertainties surrounding particle properties and their impact on human health and the climate remain. To expand on the limited understanding this laboratory study investigated the physicochemical characteristics of particles emitted from smouldering Irish peat. Properties investigated included number and mass emission factors (EFs), size distribution, morphology, and chemical composition. Fine particles with a diameter less than 2.5 μm (PM_2.5), accounted for 91 ± 2% of the total particle mass and the associated mass EF was 12.52 ± 1.40 g kg^-1. Transmission electron microscopy imaging revealed irregular shaped metal particles, spherical sulfate particles, and carbonaceous particles with clusters of internal particles. Extracted particle-bound metals accounted for 3.1 ± 0.5% of the total particle mass, with 86% of the quantified metals residing in the fraction with a diameter less than 1 μm. Redox active and carcinogenic metals were detected in the particles, which have been correlated with adverse health effects if inhaled. This study improves the understanding of size-resolved particle characteristics relevant to near-source human exposure and will provide a basis for comparison to other controlled and natural peatland fires.

The diversity of biogenic volatile organic compounds (BVOCs) emitted by Sitka spruce (Picea sitchensis) saplings, housed in a plant growth chamber, has been investigated using a combination of on-line (time-of-flight chemical ionisation mass spectrometry) and off-line (gas chromatography-mass spectrometry) measurement techniques. In total, 74 BVOCs were identified in the Sitka spruce emissions, considerably more than reported previously. Among the emitted BVOCs, 52 were oxygenated compounds, with piperitone (C₁₀H₁₆O), an oxygenated monoterpene, being the most abundant. Other prevalent emissions included isoprene, five monoterpenes (myrcene, β-phellandrene, δ-limonene, α-pinene, and camphene), cinnamaldehyde and camphor. Temperature and photosynthetic photon flux density (PPFD) were found to be the main drivers of emissions, with BVOCs exhibiting a range of responses to these factors. Three different plant growth cycles were used to identify the emission pathways (pooled or biosynthetic) for each BVOC, through determination of the relationships of the emission flux with temperature and with PPFD. During these cycles, all BVOCs showed clear diurnal patterns that were highly reproducible during consecutive days. The majority of the BVOCs emitted by Sitka spruce were found to originate from biosynthetic and pooled pathways simultaneously, with those from one sapling having a much lower contribution from the biosynthetic pathway. Standardised emission fluxes (temperature 30 °C and PPFD 1000 μmol m⁻² s⁻¹) were calculated for all BVOCs using the appropriate standardisation model (pooled, biosynthetic or combined). Standard emission factors were calculated to be 17.29 μg g_dw⁻¹ h⁻¹ for piperitone, 6.3 μg g_dw⁻¹ h⁻¹ for isoprene and 0.93 μg g_dw⁻¹ h⁻¹ for monoterpenes, indicating that Sitka spruce is a strong BVOC emitter.

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While photochemical aging is known to alter secondary organic aerosol (SOA) properties, this process remains poorly constrained for anthropogenic SOA. This study investigates the photodegradation of SOA produced from the hydroxyl radical-initiated oxidation of naphthalene under low- and high-NO _x conditions. We used state-of-the-art mass spectrometry (MS) techniques, including extractive electrospray ionization and chemical ionization MS, for the in-depth molecular characterization of gas and particulate phases. SOA were exposed to simulated irradiation at different stages, i.e., during formation and growth. We found a rapid (i.e. >30 min) photodegradation of high-molecular-weight compounds in the particle-phase. Notably, species with 20 carbon atoms (C₂₀) decreased by 2/3 in the low-NO _x experiment which was associated with particle mass loss (∼12%). Concurrently, the formation of oligomers with shorter carbon skeletons in the particle-phase was identified along with the release of volatile products such as formic acid and formaldehyde in the gas-phase. These reactions are linked to photolabile functional groups within the naphthalene-derived SOA products, which increases their likelihood of being degraded under UV light. Overall, photodegradation caused a notable change in the molecular composition altering the physical properties (e.g., volatility) of naphthalene-derived SOA.

South Africa has been ranked among the top ten mercury (Hg) emitters globally, with emissions from coal-fired power plants being the most significant contributor. The expansion of atmospheric Hg measurement networks in southern Africa is vital within the global context but is constrained by high costs and logistics. Passive air samplers were developed to address these issues and expand atmospheric monitoring networks. A commercially available passive sampler widely used for atmospheric Hg monitoring is the Mercury Passive Air Sampler (MerPAS®). Therefore, this study aimed to statistically evaluate the performance of these samplers in the unique South African environment by comparing Hg concentrations determined with MerPAS® with active in situ atmospheric Hg measurements conducted in this region. Measurements were conducted from June 2021 to September 2022 at the Welgegund atmospheric monitoring station, considered one of Africa's most comprehensively equipped atmospheric measurement sites. Hg concentrations measured with MerPAS® were derived for different sampling rates (SR), i.e. the original SR (OSR) provided by the supplier and an adjusted original SR (AOSR) derived using the OSR with adjustments for mean temperature and wind speed. Statistical analyses, including Kruskal–Wallis, Mann–Whitney U, Bland–Altman, and Spearman correlation tests, were used to assess the performance of MerPAS®. The OSR overestimated Hg concentrations by 16%, while the AOSR reduced this overestimation to 10%, improving alignment with active sampling data. The Mean Normalized Difference (MND) also decreased from 17.4% with OSR to 12.7% with AOSR, indicating greater accuracy. Spearman correlation analysis showed moderate agreement between passive and active sampling, with correlation coefficients of 0.39 for OSR and 0.58 for AOSR, supporting the improved comparability of AOSR. Seasonal patterns were consistent across both methods, with elevated Hg levels observed in winter due to atmospheric inversions and increased emissions. Despite a slight positive bias, the Bland–Altman analysis further confirmed good reliability between the AOSR and active measurements. This study demonstrates that MerPAS®, when calibrated for local environmental conditions, provides an accurate, cost-effective alternative for Hg monitoring, offering a feasible solution for expanding networks in regions with limited resources. By enabling broader and more accessible atmospheric Hg data collection, MerPAS® can support critical environmental policies, such as the Minamata Convention, and deepen scientific understanding of Hg dynamics in under-monitored areas like southern Africa. These findings lay the groundwork for enhancing global Hg monitoring, contributing essential insights into regional pollution and atmospheric processes across diverse environments.

Forward trajectories of trans-Atlantic dust plumes were studied over a 14 year period (N ∼500 000) with a focus on ambient meteorological conditions affecting the survivability of the microorganisms co-transported with dust. Major dust transport patterns that emerged from the ensemble of trajectories closely follow the established seasonal transport patterns of African dust over the tropical Atlantic Ocean: summer transport (June–August) reaching the southeastern US and the Caribbean at an average altitude of 1600 m and winter transport (December–February) reaching the Amazon basin at around 660 m. Summer trajectories take on average 270 hours to cross the Atlantic, while winter ones take 239 hours. A higher diversity is expected in microorganisms co-transported to the Amazon due to the higher diversity in contributing dust emission sources. Analysis of meteorological conditions along the trajectories indicate more favorable conditions for microorganism survival reaching the Amazon. During the winter and for Amazon trajectories, lower mean solar radiation flux of 294 W m⁻² and mean relative humidity levels at around 61% are observed as compared to averages of 370 W m⁻² solar radiation and 45% relative humidity for summer trajectories entering the Caribbean basin. Nevertheless, 14% of winter trajectories (4664 out of 32 352) reaching the Amazon basin face intense precipitation, potentially removing microorganisms, as compared to 8% of trajectories (2540 out of 31 826) entering the Caribbean basin during the summer. These findings have important implications for the survivability of microorganisms in trans-Atlantic dust plumes and their potential for major incursion events at receptor regions.

Gaseous and particulate-bound oxidized mercury (Hg) compounds (Hg^II) have high solubility in precipitation compared to gaseous elemental Hg (Hg⁰). Wet and dry deposition are the primary routes of entry for atmospheric Hg^II into aquatic ecosystems. Information on how much Hg^II is removed from the atmosphere to the landscape during precipitation is lacking. In this study, oxidized Hg^II concentrations were measured with a dual-channel system (DCS) at two sites in the United States, Storm Peak Laboratory (SPL), in Colorado (2021–2022), and Beltsville (MD99) in Maryland (2022–2024), and compared with data from 16 co-located Atmospheric Mercury Network (AMNet) and Mercury Deposition Network (MDN) sites that used a KCl denuder method. At the two DCS sites, gaseous oxidized Hg concentrations were segregated by wet and dry periods from the nearest precipitation gauge to determine values for median dry Hg^II and median wet Hg^II concentrations (dry-wet = “Hg^II washout”) for each site. SPL had higher median ambient Hg^II and higher median Hg^II washout (90 pg m⁻³ and 22 pg m⁻³, respectively) compared to that for MD99 (43 pg m⁻³ and 7 pg m⁻³). This difference could be due to site elevation (3161 vs. 77 m) as there is generally more Hg^II higher in the atmosphere. In contrast, the ambient Hg^II/washout Hg^II ratios were more similar, 4.1 for SPL and 5.8 at MD99. The mean ambient Hg^II/washout Hg^II ratio for the 16 AMNet sites was 1.8 ± 0.1. The AMNet Hg^II data are known to be biased low due to issues with the KCl-denuder method, and this low bias appears to result in lower ambient Hg^II/washout Hg^II ratio observed for the AMNet sites. Correction factors for AMNet data using Hg^II measurements from DCS instruments were found to range from 2–3 and could be used to improve the accuracy of older data.