Environmental science: atmospheres最新文献

Despite its low atmospheric concentration, mercury in particulate matter (PHg) significantly impacts its biogeochemical cycle. This research focused on the airborne Hg concentrations in fine particulate matter (PM_2.5) collected from three distinct sites: an urban area, an urban area affected by sugarcane burning, and protection reserve area within the state of Rio de Janeiro, Brazil, across various seasons during 2022–2023. The findings revealed average concentration of PM_2.5 in Gávea was 19 ± 8 μg m⁻³ (with values ranging from 8 to 37 μg m⁻³), in PARNASO, it was 24 ± 11 μg m⁻³ (with values ranging from 0.2 to 46 μg m⁻³), and in Campos, it was 10 ± 6 μg m⁻³ (with values ranging from 1 to 19 μg m⁻³). Given these values, no day surpassed the threshold outlined by Brazilian regulations. However, 63% of the samples showed daily concentrations exceeding the standards established by the World Health Organization. The average mercury concentrations in PM_2.5 were 81 ± 116 (3–366) pg m⁻³, 169 ± 139 (2–392) pg m⁻³, and 110 ± 71 (8–272) pg m⁻³ for the urban region of the capital, interior with sugarcane burning and forest locations, respectively, throughout the study period. The study also found that PHg concentrations were about twice as high during the dry period compared to the summer season, suggesting contributions from both local sources and transboundary pollution. Furthermore, significant seasonal variation in PHg concentrations was observed, with notably higher levels detected in the interior urban area impacted by burns than in the capital and preserved sites.

Isoprene affects new particle formation rates in environments and experiments also containing monoterpenes. For the most part, isoprene reduces particle formation rates, but the reason is debated. It is proposed that due to its fast reaction with OH, isoprene may compete with larger monoterpenes for oxidants. However, by forming a large amount of peroxy-radicals (RO₂), isoprene may also interfere with the formation of the nucleating species compared to a purely monoterpene system. We explore the RO₂ cross reactions between monoterpene and isoprene oxidation products using the radical Volatility Basis Set (radical-VBS), a simplified reaction mechanism, comparing with observations from the CLOUD experiment at CERN. We find that isoprene interferes with covalently bound C₂₀ dimers formed in the pure monoterpene system and consequently reduces the yields of the lowest volatility (Ultra Low Volatility Organic Carbon, ULVOC) VBS products. This in turn reduces nucleation rates, while having less of an effect on subsequent growth rates.

Near-explicit chemical mechanisms representing toluene SOA formation are reduced using the GENOA algorithm and used in 3D simulations of air quality over Greater Paris and in the streets of a district near Paris. The SOA concentrations formed by the toluene photo-oxidation are found to mostly originate from molecular rearrangement with ring opening of a bicyclic peroxy radical (BPR) with an O–O bridge (45%), followed by OH-addition on the aromatic ring (22%), Highly Oxygenated organic Molecules (HOM) formation without ring opening (13%), condensation of methylnitrocatechol (8%), irreversible formation of SOA from methylglyoxal (6%), and ring-opening pathway (3%). The concentrations simulated using the most comprehensive reduced chemical scheme (rdc. Mech. 3) are also compared to those simulated with a SOA scheme based on chamber measurements, and one reduced from the Master Chemical Mechanism. Using rdc. Mech 3 leads to between 50% and 75% more toluene SOA concentrations than the other schemes, mostly because of molecular rearrangement. The SOA compounds from rdc. Mech. 3 are more oxidized and less volatile, with molecules of different functional groups. Concentrations of methylbenzoquinones, which may be of particular health interest, represent about 0.5% of the toluene SOA concentrations. Those are slightly higher in streets than in the urban background (by 2%).

Sea-spray aerosols (SSAs) contribute to atmospheric loading, bringing toxic compounds like mercury (Hg) to the atmosphere, affecting the climate and human health. Despite their importance, the investigation into surface modification, including heterogeneous chemical and photochemical reactions of SSAs, is limited. In this work, we studied the heterogeneous chemistry and photochemistry of a single suspended SSA particle and a SSA containing Hg(II) in a reactive environment using optical trapping – Raman spectroscopy. The experiments are focused on the study of hygroscopicity, heterogeneous chemical reaction with ozone (O₃), photochemical reaction with UVC radiation of an optically suspended single SSA particle, and photo-reduction of Hg(II) in SSAs under UVC radiation. Results show different Raman signal responses of a single SSA particle when it is optically trapped in air under varying relative humidity conditions as the aerosol particle uptakes and loses liquid water from the surrounding environment. The state and size of the aerosol are determined through the on-time images and different single-particle Raman spectral features. Results also show that the formation of chlorate (ClO₃⁻) is a reaction product of the heterogeneous reaction between the SSA particle and O₃. The photochemical reaction products, as the SSA particle suspended in air under UVC radiation, are ClO₃⁻ and perchlorate (ClO₄⁻). Further, we observed that these reactions occur only on the surface of the SSA particle. Based on the results, we hypothesize that Hg(II) can be photo-reduced to Hg(I) in SSAs through UVC radiation, and the amount of Hg(I) in SSAs is minor and balanced between the photo-oxidation and photo-reduction reactions.

Biomass burning is an important source of primary and secondary organic aerosol (POA, SOA, and together, OA) to the atmosphere. The photochemical evolution of biomass burning OA, especially over long photochemical ages, is highly complex and there are large uncertainties in how this evolution is represented in models. Recently, Lim et al. (2019) performed and reported on photooxidation experiments of biomass burning emissions using a small environmental chamber (∼150 L) to study the OA evolution over multiple equivalent days of photochemical aging. In this work, we use a kinetic, process-level model (SOM-TOMAS; Statistical Oxidation Model-TwO Moment Aerosol Sectional) to simulate the photochemical evolution of OA in 18 chamber experiments performed on emissions from 10 different fuels. A base version of the model was able to simulate the time-dependent evolution of the OA mass concentration and its oxygen-to-carbon ratio (O : C) at short photochemical ages (0.5 to 1 equivalent days). At longer photochemical ages (>1 equivalent day), the model exhibited poor skill in predicting the OA mass concentration and significantly underestimated the OA O : C. The modeled OA after several equivalent days of photochemical aging was slightly dominated by SOA (average of 57% across all experiments) with the remainder being POA (average of 43% across all experiments). Semi-volatile organic compounds, oxygenated aromatics, and heterocyclics accounted for the majority (89%, on average) of the SOA formed. Experimental artifacts (i.e., particle and vapor wall losses) were found to be much more important in influencing the OA evolution than other processes (i.e., dilution, heterogeneous chemistry, and oligomerization reactions). Adjustments to the kinetic model seemed to improve model performance only marginally indicating that the model was missing precursors, chemical pathways, or both, especially to explain the observed enhancement in OA mass and O : C over longer photochemical ages. While far from ideal, this work contributes to a process-level understanding of biomass burning OA that is relevant for its extended evolution at regional and global scales.

The first measurements of HO₂ uptake coefficients (γ_HO2) onto suspended aerosol particles as a function of temperature are reported in the range 314 K to 263 K. For deliquesced ammonium nitrate (AN) particles γ_HO2 increases from 0.005 ± 0.002 to 0.016 ± 0.005 as the temperature is lowered over this range. For effloresced sodium chloride and ammonium sulphate particles, γ_HO2 decreases slightly from 0.004 ± 0.002 to 0.000 ± 0.002 and 0.002 ± 0.003, respectively, between 314 and 263 K. For AN particles doped with Cu²⁺ ions, we find γ_HO2 ≈ α_HO2, the mass accommodation coefficient, which increases very slightly from α_HO2 = 0.62 ± 0.05 to 0.71 ± 0.06 between 292 and 263 K with lowering temperature. New measurements of γ_HO2 are also reported for ammonium sulphate particles doped with a range of Fe²⁺ and Fe³⁺ concentrations. The dependence of γ_HO2 on Cu and Fe concentrations are reconciled with published rate coefficients using the kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB). The model shows that in experimental studies using aerosol flow tubes, a time dependence is expected for γ_HO2 onto aerosol particles which do not contain transition metal ions due to a decrease in the gas-phase concentration of HO₂ as a function of time. The model also demonstrates that Fenton-like chemistry has the potential to decrease γ_HO2 as a function of time for particles containing transition metal ions. For atmospherically relevant transition metal ion concentrations in aerosol particles, γ_HO2 can take a range of values depending on pH and the particle size from γ_HO2 < 0.04 to γ_HO2 = α_HO2. γ_HO2 for larger particles (radius ≥ 0.5 μm) can be significantly reduced by gas-diffusion limitations.

Total precipitable water (TPW) is a key player in the global water cycle, shaping our climate and impacting extreme weather phenomena such as tropical storms and monsoons. Its presence, varying across regions and seasons, is the highest in warm oceanic regions, particularly in the tropics and subtropics, while polar regions see the least. Multiple satellite observations provide compelling evidence of a positive and statistically significant trend in TPW, indicating a notable increase at a rate of 0.037 kg per m⁻³ per year. Ocean temperatures vary regionally; the North Atlantic Ocean (NAO) warms at 0.02–0.03 °C per year and South Atlantic Ocean (SAO) warms slower at 0.015–0.020 °C per year. The Equatorial and Northeastern Pacific warm at 0.038–0.040 °C per year. The Indian Ocean (IO) warms the fastest at 0.1–0.18 °C per year, and Southern Ocean (SO) and Atlantic Ocean (AO) show mixed trends, including cooling. The intricate relationship between natural climate indices and the global TPW received strong positive feedback from the Pacific decadal oscillation (PDO) and oceanic Niño index (ONI), indicating their profound impact on TPW. The Western Pacific index (WP) exhibits a direct and strong positive feedback loop and a strong relationship of PDO and ONI with TPW. Increasing the α level enhances connections, notably between the multivariate ENSO index (MEI) and dipole mode index (DMI). Interactions between these indices and TPW unveil interconnected climatic processes affecting atmospheric moisture. Recognizing these dynamics is crucial for accurate climate predictions, given the reinforcement of positive feedback loops.

This study investigates the light absorption properties of organic aerosols in PM₁₀ collected at a high-altitude location (2700 m a.s.l.) in the eastern Himalayas from March 2019 to February 2020. The analysis reveals an enhanced light-absorbing signature of methanol-soluble brown carbon (MeS-BrC) extracts compared to water-soluble brown carbon (WS-BrC) within the optical wavelength range of 300–700 nm. MeS-BrC exhibits approximately twice the absorption compared to that of WS-BrC at 365 nm. The highest light absorption coefficients at 365 nm (b_abs365) are observed during spring for both MeS-BrC (9 ± 4.6 Mm⁻¹) and WS-BrC (5.9 ± 4.2 Mm⁻¹). Notably, the contribution of absorption from the water-insoluble fraction is relatively higher during the summer monsoon (45.2 ± 19.5%) and autumn (44.1 ± 18.4%). A significant linear relationship between WSOC and WS-BrC as well as OC and MeS-BrC at 365 nm suggests similar sources for BrC and WSOC (OC). Furthermore, significant positive correlations of b_abs365 (WS-BrC and MeS-BrC) with the water-soluble fraction of total nitrogen (WSTN) and organic nitrogen (WSON) indicate the presence of nitrogenous organic chromophores playing a crucial role in BrC absorption during spring and autumn. The mass absorption efficiency at 365 nm (MAE₃₆₅) reveals that BrC in spring aerosols (WS-BrC: 1.5 ± 0.6 m² g⁻¹; MeS-BrC: 2.07 ± 0.8 m² g⁻¹) absorbs UV-visible light more efficiently compared to aerosols collected during other seasons. The enhanced MAE₃₆₅ during spring resulted the highest simple forcing efficiency of 8.7 ± 3.9 W g⁻¹ and 10.8 ± 5.2 W g⁻¹ for WS-BrC and MeS-BrC, respectively, for a specific solar geometry and surface properties. This may be attributed to intense biomass burning followed by atmospheric processing of organic aerosols in the aqueous phase. These findings confirm the significant role of anthropogenic sources in enhancing BrC light absorption and radiative effects in this highly sensitive region of the eastern Himalayas. Such insights are crucial for devising effective strategies for mitigating climate change impacts in the Himalayan ecosystem.

Oxidation flow reactors (OFRs) have been increasingly used to conduct research on secondary aerosol formation potential and composition in laboratory and field studies by exposing aerosols to high levels of oxidants in short time periods. In order to assess the atmospheric relevance of the triggered chemical reactions, kinetic models have been developed to reveal the production of atmospheric oxidants and the fate of volatile organic compounds (VOCs). However, it is unknown how different OFR conditions generating the same OH exposure affect the chemical and physical properties of the secondary aerosol particle phase because the model is based on gas phase chemistry. Toluene as a well-investigated precursor of secondary organic aerosols (SOAs) was aged in the high-volume OFR “PEAR” at three different external OH reactivities (OHR_ext) and in an environmental chamber at the same OH exposure of (1.09 ± 0.09) × 10¹¹ s cm⁻³. These specific OFR conditions altered the majority of the investigated chemical and physical properties of the toluene-derived SOA (tol-SOA). However, OFR-aging at low OHR_ext associated with atmospherically relevant conditions did not lead to physical and chemical SOA properties most similar to chamber-generated SOAs at the same low OHR_ext. Particularly, for the most detailed chemical analysis by electrospray (ESI) high-resolution Orbitrap mass spectrometry (HRMS), tol-SOA from the PEAR at high OHR_ext, deviating from atmospherically relevant conditions, and the chamber were most different to tol-SOA from the PEAR with low and medium OHR_ext. Our study challenges the concept of atmospherically relevant OFR aerosol aging and motivates further exploration of OFR conditions on secondary aerosol composition.

The most recent European regulation, the Euro 6d emission standard, requires all gasoline direct injection (GDI) vehicles to use both a three-way catalyst (TWC) and a gasoline particle filter (GPF) as exhaust aftertreatment. These aftertreatment methods are aimed at reducing NO_x and primary particle emissions. However, the formation of secondary organic aerosols (SOAs) from the volatile organic compound (VOC) emissions of a Euro 6d compliant GDI vehicle, factory equipped with a GPF is not yet investigated. Therefore, to explore the SOA formation and effects of the GPF, the exhaust of a Euro 6d compliant GDI vehicle was characterized at 4 different steady state speeds, idling (0 km h⁻¹), 50, 80 and 100 km h⁻¹. The exhaust was oxidised in a photochemical emission aging flow tube reactor (PEAR) by reactions with OH radicals equivalent of 2.2 days of atmospheric day time oxidation. It was found that the GPF completely removes primary particles larger than 10 nm, at all investigated vehicle speeds. However, significant SOA was formed after oxidation, with the highest SOA formation potential per kg fuel consumed at 50 km h⁻¹. The main SOA precursors were determined to be toluene, xylene and trimethyl-benzene which were found to account for at least 50% of SOA formed at all driving speeds. Furthermore, high emissions of ammonia (NH₃) could be observed in the exhaust under all driving conditions which resulted in the subsequent formation of ammonium nitrate (NH₄NO₃) after aging. The formation of NH₄NO₃ additionally facilitated the co-condensation of organic gas phase products after OH oxidation enhancing SOA mass even further.