Environmental science: atmospheres最新文献

In recent work [Daub et al., ACS Earth Space Chem., 2022, 6, 2446] we have developed a simple model for describing the lifetime of pre-reactive complexes, and demonstrated its use for predicting the reactivity of barrierless reactions between peroxy radicals. Here, we modify and extend the method in three important ways. First, we compare the use of a Langevin thermostat for initial equilibration of the system with the Nosé–Hoover thermostat. Then, we show some new results for the lifetimes of complexes of secondary and tertiary ozonolysis and hydroxyl radical products from α-pinene. Finally, we use the method to measure the temperature dependence of complex lifetimes and compare them with available experimental results for reaction rates as a function of temperature.

Bioaerosol samples are characterized by very low biomass, so culture-based detection remains a reliable and acceptable technique to identify and quantify microbes present in these samples. The process typically involves the generation of bacterial colonies by inoculating the sample on an agar plate, followed by the identification of colonies through DNA sequencing of a PCR-amplified targeted gene. The Sanger method is often the default choice for sequencing, but its application might be limited in identifying multi-species microbial colonies that could potentially form from bacterial aggregates present in bioaerosols. In this work, we compared Sanger and MinION nanopore sequencing techniques in identifying bioaerosol-derived bacterial colonies using 16S rRNA gene analysis. We found that for five out of the seven colonies examined, both techniques indicated the presence of the same bacterial genus. For one of the remaining colonies, a noisy Sanger electropherogram failed to generate a meaningful sequence, but nanopore sequencing identified it to be a mix of two bacterial genera. For the other remaining colony, the Sanger sequencing suggested a single genus with a high sequence alignment and clean electropherogram; however, the nanopore sequencing suggested the presence of a second less abundant genus. These findings were further corroborated using mock colonies, where nanopore sequencing was found to be a superior method in accurately classifying individual bacterial components in mock multispecies colonies. Our results show the advantage of using nanopore sequencing over the Sanger method for culture-based analysis of bioaerosol samples, where direct inoculation to a culture plate could lead to the formation of multispecies colonies.

We investigated the fuel-dependent single-particle mass spectrometric signatures of polycyclic aromatic hydrocarbons (PAHs) from the emissions of a research ship engine operating on marine gas oil (MGO), hydrotreated vegetable oil (HVO) and two heavy fuel oils (HFO), one with compliant and one with non-compliant fuel sulfur content. The PAH patterns are only slightly affected by the engine load and particle size, and contain sufficient dissimilarity to discriminate between the marine fuels used in our laboratory study. Hydrotreated vegetable oil (HVO) produced only weak PAH signals, supporting that fuel residues, rather than combustion conditions, determine the PAH emissions. The imprint of the fuel in the resulting PAH signatures, combined with novel single-particle characterization capabilities for inorganic and organic components, opens up new opportunities for source apportionment and air pollution monitoring. The approach is independent of metals, the traditional markers of ship emissions, which are becoming less important as new emission control policies are implemented and fuels become more diverse.

Intense episodes of fine particulate matter (PM_2.5) pollution often overwhelm large areas of the Indo-Gangetic Plain (IGP) in northern India during the post-monsoon season, a time when crop residue burning is at its peak. We conduct idealised emission sensitivity experiments using the WRF-Chem model to investigate the leading causes and spatiotemporal extent of one such extreme episode from 31 Oct to 8 Nov 2016, when hourly PM_2.5 levels exceeded 500 μg m⁻³ across much of the IGP on several days. We utilise the anthropogenic emissions from EDGARv5.0 and the latest FINNv2.5 for fire emissions and evaluate modelled and observed ambient PM_2.5 and black carbon (BC) concentrations across the IGP. The model captured the PM_2.5 and BC peaks during the latter half of the episode and underestimated on other days. We find that biomass burning (BB) emissions during this episode have the strongest effect across the source regions in the upper (NW) IGP, followed by Delhi (middle IGP), where it contributes 50–80% to 24 h mean PM_2.5. Complete elimination of BB emissions decreases PM_2.5 concentrations by 400 μg m⁻³ (80–90%) in the upper IGP and by 280 μg m⁻³ (40–80%) across the middle IGP during this episode. Contributions from the BB source to daily varying BC concentrations are 80–90%, 40–85% and 10–60% across upper, middle and lower IGP, respectively. BB emissions dominantly contribute to daily mean secondary organic aerosols (80%), primary organic aerosols (90%), dust (60%), and nitrate (50%) components of PM_2.5 across the upper and middle IGP. In comparison, the anthropogenic share of these compounds was nearly one-third everywhere except across the lower IGP. The buildup of the episode across the middle IGP was facilitated by prolonged atmospheric stratification and stagnation, causing BB-derived BC and PM_2.5 to be trapped in the lowest 1 km. Our work emphasises the need for rigorous policy interventions during post-monsoon to reduce agricultural crop burning, together with targeted anthropogenic emissions control across the IGP, to minimise such extreme episodes in the future.

The formation of HNO₃ gas over the Yellow Sea and its impact on particulate nitrate concentrations in Seoul during the PM_2.5 episode in Seoul in January 2018 were studied by analyzing monitoring data and running WRF-CMAQ model simulations. Monitoring data showed that particulate nitrate made up 41% of the PM_2.5 during the episode, 2.7 times more than in other periods, and its level was strongly correlated with PM_2.5 mass, indicating that the particulate nitrate is the primary cause of the episode. During the episode, eastern China was in slight to moderate ammonia-rich conditions and Seoul had slight ammonia-rich conditions. In contrast, severe ammonia-lean conditions prevailed in the Yellow Sea. Despite the decline of solar radiation at night, the production rate of HNO₃ in the Yellow Sea still increased slightly due to the higher nocturnal ozone levels compared to the daytime. On the other hand, it decreased in eastern China and western Korea during the night as O₃ dissipated by NO titration, resulting in the conversion rates of NO₂ to HNO₃ in the Yellow Sea being several times higher than those in eastern China and western Korea. The HNO₃ gas formed in the Yellow Sea was transported to Seoul under westerly winds, contributing to particulate nitrate formation. Furthermore, the rate of formation of HNO₃ gas in the Yellow Sea was 65% higher than that in Seoul during the night, which indicated that the regional influence dominated the local influence in determining the particulate nitrate concentrations in Seoul.

The capture vaporizer (CV) was developed to reduce uncertainties in non-refractory aerosol composition measurements made using the aerosol mass spectrometer (AMS) and the aerosol chemical speciation monitor (ACSM). Use of the capture vaporizer has achieved this by improving the instruments' collection efficiency to ∼1, but it has also lengthened the aerosol particles' residence times in the instrument, which has changed AMS and ACSM measurements using the standard vaporizer by altering known fragmentation patterns of organic marker species and increasing the likelihood of detecting refractory particles such as sea salt at typical operating temperatures (∼550 °C). This study reports that the changes affected by the capture vaporizer leads to sea salt particles interfering with measurements of biomass burning organic aerosols (BBOA) in environments where both particle sources are present as the ACSM's unit mass resolution is unable to distinguish between different molecules with the same molecular mass. Demonstration of this interference was performed using CV-Time of Flight-ACSM (CV-ToF-ACSM) measurements at two coastal Australian locations: the Kennaook-Cape Grim Baseline Air Pollution Station, Tasmania; and the site of the COALA-2020 (Characterizing Organics and Aerosol Loading over Australia 2020) campaign in New South Wales. Concentrations of BBOA marker ions m/z 60 and m/z 73 were examined at both locations, which showed two distinct branches of points: one where the two marker ions were positively correlated and one that was uncorrelated. This was due to m/z 60 also being a marker for sea salt. A threshold concentration of m/z 73 was established at each location to recognise periods where m/z 60 originated from BBOA. Lower concentrations of m/z 44 and radon when m/z 73 concentration was below the BBOA threshold indicated that m/z 60 concentration during these periods corresponded to inorganic particles of marine origin. Positive Matrix Factorization has also been shown to separate m/z 60 concentration from the two sources. This study suggests that using CV-ToF-ACSMs in coastal locations that are exposed to biomass burning smoke needs to consider sea salt interference when identifying BBOA.

Fairbanks-North Star Borough, Alaska (FNSB) regularly experiences some of the worst wintertime air quality in the United States. Exceedances of the EPA's 24 h fine particulate matter (PM_2.5) rule are common, and can last for weeks-long periods. Here we present sub-hourly measurements of chemically-speciated aerosol measurements over a 25 month span from an Aerosol Chemical Speciation Monitor (ACSM). This dataset includes measurements from all four seasons and over three separate winters (2020, 2021, 2022). It spans a long enough duration to provide an overview of typical seasonal and diurnal variations in aerosol concentrations, composition, and sources in Fairbanks. We observe consistent high PM_2.5 concentrations in wintertime, which is dominated by organic aerosol (OA) and, to a lesser extent, sulfate (SO₄). We perform factor analysis of the OA using Positive Matrix Factorization (PMF), which reveals three factors, two of which are attributable to primary sources. These primary OA factors are highest in concentration and fractional contribution during wintertime. We show that high concentration periods are correlated with cold temperatures, and enriched in those organic aerosol components related to primary emissions. High concentration periods are also enriched in SO₄, though we show that some of the “SO₄” measured by the ACSM is very likely organosulfur compounds, which are more prevalent at high concentrations. We also show that within winter, there are significantly different diurnal patterns in PM components depending on meteorological parameters. This analysis is important for understanding air quality patterns in Fairbanks, and as context for the 2022 ALPACA measurement campaign.

Polycyclic aromatic compounds (PACs) encompass a range of organic pollutants, including polycyclic aromatic hydrocarbons (PAHs), alkyl-substituted PAHs (AlkPAHs), and others. PAHs have been extensively studied due to their environmental and health implications. AlkPAHs, however, have received relatively less attention, despite recent evidence suggesting their greater abundances in ambient air. Given their prevalence and potential risks, investigating the atmospheric transformation of AlkPAHs is crucial. This work focuses on the heterogeneous oxidation of AlkPAHs, specifically addressing the influence of alkyl groups on reaction kinetics. Oxidation by gas phase ozone was conducted on quartz filters, which serve as models for silica surfaces on which PACs can deposit with minimal chemical interactions. The results reveal that AlkPAHs react faster with ozone than PAHs do, with reaction rates increasing with higher alkyl group substitutions. Furthermore, oxygenated polycyclic aromatic hydrocarbons (OPAHs) were formed during the oxidation of 1-methylpyrene, with greater diversity than those from pyrene. These products are more polar and potentially more toxic than parent compounds. In conclusion, this research advances our understanding of PAC oxidation, focusing on AlkPAHs' heterogeneous oxidation, the influence of alkyl groups, and the formation of OPAHs. These insights have significant implications for air quality, health risk assessments, and the fate of PACs in the environment.

The development of catastrophic mesoscale convective systems in the atmosphere, such as thunderstorms, is caused by several factors, the most important of which is moisture in the lower troposphere and then the instability and lifting of air parcels. In pre-monsoon, northeast and adjoining eastern India are susceptible to thunderstorms. Herein, we analyse the spatial and temporal changes in thunderstorm activities in terms of convective available potential energy (CAPE) and other parameters during the pre-monsoon period (March, April and May) in northeast (NE) and adjoining eastern India using ground-based and reanalysis data. It is observed that atmospheric instability is relatively higher in southern West Bengal and Tripura compared to the other regions in NE and adjoining eastern India, with a CAPE value of about 1500–3000 J kg⁻¹ during pre-monsoon and 2000–3500 J kg⁻¹ in May, indicating that these regions are more vulnerable to thunderstorms. Other thunderstorm indicators such as convective inhibition (CIN), K-index (KI) and total totals index (TTI) also exhibit relatively higher values in these regions during pre-monsoon. Causal discovery and correlation analysis reveal a positive association of thunderstorm days with CAPE and TTI, but a negative link with CIN. A significant negative trend is estimated in CAPE and other parameters in NE and eastern India during May, which is more dominant in southern West Bengal and Tripura (about −8 to −12 J per kg per year). Stability indices such as KI and TTI also show significant negative trends in NE India. There is a negative trend in thunderstorm days at Mohanbari, Barapani, Jorhat, Pasighat and Silchar, while positive trends at Dhubri, Imphal, Tezpur and Lengpui in the recent decade (2011–2020), which is consistent with the changes in thunderstorm indicators at these stations. This study provides an important insight into thunderstorm activity in areas susceptible to extreme weather events in the context of recent climate change and global warming.

Monitoring and control of indoor air hygiene has gained much interest since the COVID-19 pandemic because the airborne route is the main pathway for the spread of SARS-CoV-2 and other pathogens, making it necessary to develop strategies to mitigate airborne transmission of diseases. This work addresses indoor breathable air hygiene by proposing the “in situ” reduction of airborne microorganisms with the nebulization of low and safe concentrations of hydrogen peroxide (H₂O_2, 0.5 and 1 ppm), ozone (O_3, 0.06 and 0.2 ppm), triethylene glycol (TEG, 17.1, 52 and 171.2 ppm), and their combinations. The antimicrobial activity was evaluated in an office room by assessing the viability of commercial extremophile sporulated bacteria and naturally present bacteria and fungi in surfaces and air. All three chemicals individually dispersed reduced the viability of sporulated bacteria and naturally occurring microorganisms. Binary combinations were more effective than individual agents in the case of the H₂O₂ and O₃ mixture against sporulated bacteria, and the O₃ and TEG mixture against airborne and surface bacteria. The ternary mixture was the most effective against commercial sporulated bacteria and airborne microorganisms. These results illustrate that the application of low and safe concentrations of antimicrobial compounds in indoor air could be an interesting strategy to reduce infection risk.