Environmental science: atmospheres最新文献

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.

The peroxycarboxylic nitric anhydrides (PANs; RC(O)O₂NO₂ with R ≠ H) are important trace gas constituents of the troposphere. One of the lesser studied molecules of the PAN family is peroxyacrylic nitric anhydride (APAN; CH₂CHC(O)O₂NO₂) which is found in elevated concentration in biomass burning (BB) plumes and downwind from petrochemical plants. In this work, we conducted laboratory and field experiments to constrain the thermal decomposition (TD) rates of APAN in the atmosphere. The TD of APAN was studied in laboratory experiments using a Pyrex reaction coil at temperatures between 295.2 K and 320.7 K as a function of flow rate (i.e., residence time). Gas streams containing APAN were generated from a diffusion source containing a synthetic sample stored in tridecane at water-ice temperature. Nitric oxide (NO) was added to this gas stream to prevent recombination of the TD products. Concentrations of APAN were monitored by gas chromatography with electron capture detection (PAN-GC). The TD rate constant is best described by 10^{(17.88±0.80)} e^{−(121.2±4.8) kJ mol−1/(RT)} s⁻¹, where R is the universal gas constant, and T is the temperature in kelvin. We report ambient air mixing ratios of peroxyacetic nitric anhydride (PAN), peroxypropionic nitric anhydride (PPN), and APAN measured by PAN-GC at the Calgary Central (Inglewood) air quality station from April 17 to May 31, 2023. From May 16 to May 21, the measurement location was blanketed by a BB plume as judged from co-located observations of fine particulate matter (PM_2.5) and carbon monoxide (CO). During this time, mixing ratios as high as 3.4 ppbv (PAN), 455 pptv (PPN), and 220 pptv (APAN) were observed. After sunset, mixing ratios of the PANs decreased with pseudo-first order kinetics, rationalized by a combination of dry deposition and loss by TD.

Tobacco curing poses serious environmental and health risks from elevated airborne pollutant emissions. This study aims to identify key air pollutants and associated behaviours during tobacco curing and storage operations, focusing on their impacts on air quality and potential health risks. This in situ analysis was conducted over 24 h at six tobacco curing houses (CHs) and three storage houses (SHs). Pollutant dynamics are influenced by ambient temperature and relative humidity, with higher temperatures and lower humidity amplifying emissions. Statistical analysis confirms that particulate matter (PM), total volatile organic compounds (TVOCs), HCHO, NO₂, O₃, CO, and SO₂ for both environments exceed WHO standard limits, and most pollutants follow flat distributions with occasional spikes. Indoor–outdoor ratio (I/O) analysis shows that outdoor pollution stems from biomass combustion, while indoor levels result from both outdoor diffusion and indoor emissions. Pearson's correlation, Principal Component Analysis (PCA), and cluster analysis reveal a strong correlation among TVOCs, HCHO, NO₂, and O₃, suggesting similar sources and behaviours. Air quality indices (AQIs) indicate severe degradation, with CHs reaching unhealthy and SHs reaching very unhealthy levels, primarily driven by PM, NO₂, and O₃. These pollutants pose significant threats to human health, particularly for children sleeping in SHs, with TVOCs, HCHO, NO₂, and PM primarily driving non-carcinogenic risks, and TVOCs are emerging as a major cancer risk. TVOCs, HCHO, and NO₂ also impair plant health. This research highlights severe air pollution and associated health hazards in tobacco curing and storage environments, guiding policies to reduce exposure and promote sustainable tobacco production practices.

Organic peroxy radicals (RO₂) are produced in the atmosphere by oxidation of volatile organic compounds (VOCs) and, in some cases, VOC photolysis. However, photolytic sources of RO₂ are often poorly understood, in part due to challenges in directly detecting RO₂ in both ambient and laboratory settings. We investigated Cl₂⁻ as a chemical ionization mass spectrometry reagent ion (Cl₂-CIMS) for measuring and speciating RO₂ in a laboratory setting. Cl₂-CIMS was more sensitive to the acetyl peroxy radical (CH₃C(O)O₂; 2.30 ± 0.04 ncps/ppt) than iodide CIMS (I-CIMS; 1.54 ± 0.03 ncps/ppt), but high backgrounds in our setup resulted in a slightly higher detection limit of 5 ppt (1 second integration) for Cl₂-CIMS than I-CIMS (2 ppt). We demonstrate the application of Cl₂-CIMS by quantifying the quantum yields of two radical products, CH₃C(O) and C₂H₅C(O), from methyl ethyl ketone photolysis at 254 nm. We identified O₂⁻ and Cl⁻ as possible secondary reagent ions that created unintended product ions in our experiments and thus could complicate the interpretation of Cl₂-CIMS mass spectra for complex atmospheric samples. While several strategies may minimize these effects, Cl₂-CIMS is suitable for measuring RO₂ in controlled laboratory experiments.

The gas-particle partitioning of low-volatility and semi-volatile organic compounds (L/S-VOCs) plays a dominant role in the formation of secondary organic aerosol, carrying implications for the health and climate effects of atmospheric particulate matter. Partitioning into aqueous particles and cloud droplets can also impact the fates of L/S-VOCs in the atmosphere. As the NH₃/NH₄⁺ conjugate pair begins to dominate the buffering capacity of the atmospheric aqueous phase, there is a growing need to consider how changing particle acidity may impact the phase distribution of different ionizable compounds. In this work, we use a partitioning space framework and graphical assessment method to predict the effects of varied pH and temperature on the partitioning behavior of 24 ionizable organic compounds, including carboxylic acids and amines. As pH increases from 2 to 6, amines exhibit significantly increased affinity for the gas phase, whereas a preference for the aqueous phase is generated among several weak acids that would otherwise have remained vapors. We find that temperature can have a strong influence on the partitioning of some compounds. However, temperature-dependence can vary widely between compounds, and our analysis was limited by a lack of enthalpy values, necessitating reliable thermodynamic data for a larger number of L/S-VOCs. We implement a new visualization to investigate the partitioning behavior of lesser-studied compounds under varied conditions, and through this approach we see that aerosol liquid water content can greatly impact pH-sensitivity in partitioning.

Underserved rural communities in northeastern North Carolina (NC), surrounding the Albemarle Sound, have faced degraded environmental quality from various sources of air and water pollution. However, access to local air quality data is regionally scarce due to a lack of state-run monitoring stations, which has motivated local community science efforts. In January 2022, we co-developed a community-led study to investigate the relationship between fine particulate matter (PM_2.5) and sources of regional air pollution, with a specific focus on previously identified emissions from cyanobacterial harmful algal blooms (CyanoHABs). Using low-cost PurpleAir air quality sensors to quantify PM_2.5 mass, satellite-derived indicators of CyanoHABs, and other publicly available atmospheric and meteorological data, we assessed environmental drivers of PM_2.5 mass in the airshed of the Albemarle Sound estuary during 2022–2023. We found that bias-corrected PurpleAir PM_2.5 mass concentrations aligned with composite data from the three nearest federal reference equivalent measurements within 1 μg m⁻³ on average, and that the temporal variation in PM_2.5 was most closely associated with changes in criteria air pollutants. Ultimately, satellite-based indicators of CyanoHABs (Microcystis spp. equivalent cell counts and bloom spatial extent) were not strongly associated with ambient/episodic increases in PurpleAir PM_2.5 mass during our study period. For the first time, we provide local PM_2.5 measurements to rural communities in northeastern NC with an assessment of environmental drivers of PM_2.5 pollution events. Additional compositional analyses of PM_2.5 are warranted to further inform respiratory risk assessments for this region of NC. Despite the lack of correlation between CyanoHABs and PM_2.5 observed, this work serves to inform future studies that seek to employ widely available and low-cost approaches to monitor both CyanoHAB aerosol emissions and general air quality in rural coastal regions at high spatial and temporal resolutions.