Environmental science: atmospheres最新文献

Understanding the impact of wildfire-derived biomass burning organic aerosol (BBOA) on air quality, climate, and atmospheric chemistry requires knowledge of its phase behavior and viscosity – properties that remain poorly characterized after atmospheric aging. We investigated how hydroxyl radical (OH) aging affects these properties in BBOA generated from smoldering pine wood. Samples were aged in an oxidative flow reactor with equivalent atmospheric aging times of 1.3, 5.2, and 8.6 days. Phase behavior was assessed using optical microscopy, and viscosity was measured using the poke-flow technique. Across all aging times and relative humidities (0–90% RH), particles consisted of a hydrophilic core and a hydrophobic shell. Under dry conditions, viscosity increased by 4–5 orders of magnitude with aging, and the most aged particles became glass-like. Viscosity was strongly RH-dependent. From these measurements, we estimated mixing times and glass formation in 200 nm particles throughout the troposphere. Aged BBOA is predicted to remain well mixed in the boundary layer, but in the free troposphere (∼1–12 km), mixing times often exceed 1 hour and particles are frequently in a glassy state. These findings have implications for particle growth, evaporation, and ice nucleation, and suggest that OH aging alone cannot fully explain tar ball formation in the atmosphere.

Evaluating an instrument's performance is just as important, if not more, than its intended purpose. Mass spectrometers, in particular, have been extensively studied and analyzed due to their key role in many applications across various fields. One type of mass spectrometer, the atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF MS), is widely used for measuring reactive trace gases and aerosol precursors. This study investigates the transmission efficiency of an APi-ToF MS coupled with two distinct ionization sources: an electrospray ionizer (ESI) and a nickel–chromium wire generator. Each ion source was integrated into a separate experimental setup, with the ESI paired with a planar differential mobility analyzer (P-DMA) and the wire generator combined with a Half-mini differential mobility analyzer (Half-mini DMA). The transmission efficiency was quantified by calculating the ratio of ions entering the mass analyzer to those detected at the end detector. The primary aim of this study is twofold: (1) to develop and validate a standardized procedure for quantifying transmission efficiency in APi-ToF MS systems, and (2) to critically evaluate an alternative measurement approach using a distinct ionization–mobility setup. We propose an optimized protocol for assessing transmission efficiency, providing a framework that future researchers can adapt to characterize their own instruments. Our results reveal different transmission trends between negative and positive samples, and compares the different methods explored in this study with each other and with previous studies. The ESI–P-DMA–APi-ToF MS setup was shown based on our results to be significantly more accurate, mainly since the errors on the mass/charge axis are remarkably lower, than the wire generator–Half-mini DMA–APi-ToF MS setup in determining the transmission efficiencies.

Measurements of apparent fuel sulfur content in ship exhausts (aFSC) and NO_x/CO₂ ratios were made from an airborne and ground-based platforms in the open Atlantic Ocean and the European sulfur emission control area (SECA) during multiple field campaigns from 2019 to 2023. In the open ocean a nearly 10-fold decrease in the mean aFSC demonstrates the strong impact the International Maritime Organization regulation change in 2020 had on sulfur emissions from ships. In 2019, 8 ships out of 19 showed a measured aFSC higher than the 3.5% limit at the time and in 2021 and 2022, 5 ships out of 78 were observed to be higher than the new 0.5% limit. In the SECA in the English Channel, the average aFSC across both 2019 and 2021 measurements was 0.04 ± 0.01%, well below the more stringent 0.1% limit. In the port of Valencia, Spain, which is not in a SECA, observed aFSC was on average much lower than in the open ocean and close to the EU Sulfur directive of 0.1% fuel sulfur content in port areas if the ship stays more than 2 hours in port. In the Port of Tyne (within the European SECA), the aFSC is virtually identical to those measured in the English Channel, with no ships breaching the 0.1% limit. On average, measured aFSCs agree well with the estimates of the Ship Traffic Emission Assessment Model (STEAM3), although the model does not pick up outliers that breach limits. In the open ocean in 2019 the NO_x/CO₂ ratio was 0.021 ± 0.002, with ratios observed in port significantly lower (Port of Tyne 0.009 ± 0.001, Port of Valencia 0.011 ± 0.001), with a switch to auxiliary engines in ports a potential reason for this lower emission ratio. This work presents the first aircraft-based measurements of aFSC from ships outside of sulfur control zones since the change in sulfur emission regulations in 2020 and largely justifies the assumption that is often made that ships now emit around 7 times less sulfur than before 2020.

Biomass burning emits primary organic gases and particles on a global scale, partly from domestic combustion. While there is growing understanding of the composition and characteristics of these emissions, uncertainties still exist in chemical compositions with respect to different fuel types and burning conditions. However, developments in online instrumentation have allowed for not just detailed chemical characterisation, but also the temporal resolution necessary to separate emissions according to the combustion conditions. Controlled experiments were carried out in the Manchester Aerosol Chamber to chemically characterise the composition of primary or fresh emissions from a domestic stove, using different biomass fuels, by performing controlled dilutor injections into the chamber, employing a combination of online and offline measurements, and comparing results according to different combustion phases (flaming vs. smouldering). A chemical ionization mass spectrometer coupled with a Filter Inlet for GAses and AEROsols inlet (FIGAERO-CIMS) was utilized to investigate the variations in the oxygenated (CHO) and nitrogen-containing (CHON) organic gas and particle-phase compositions, while the aerosol mass spectrometer (AMS) was employed to provide information on the primary aerosol bulk chemical composition. The CHO compounds were more abundant, contributing a higher signal fraction in wood emissions compared to leaves and peat, and with wood smouldering yielding a higher CHO fraction than flaming. The CHON compounds, though of significantly lesser contributions (<20%), were dominated by reduced nitrogen and organonitrogen compounds in the gas and particle phase respectively. The CHON compounds displayed greater aromaticity than the CHO compounds due to their higher double bond equivalent to carbon number (DBE/C) and aromaticity index (AI) values. A greater fraction of CHON compounds resulted in greater aromaticity in wood flaming compared to the smouldering emissions in the particle phase. Leaves exhibited higher aromaticity than wood and peat due to the presence of CHON compounds with greater DBE/C and AI values. Although the results showed differences in primary aerosol composition based on biomass type, the effect of burning conditions on the aerosol particles was only noticeable based on the variations in the AMS f₆₀, suggesting that the f₆₀ is a useful metric to differentiate emissions from flaming and smouldering burning phases.

Ground-level ozone (O₃) pollution in semi-arid regions like Tucson, Arizona, presents unique challenges due to the interplay of anthropogenic emissions, biogenic volatile organic compounds (BVOCs), meteorological conditions, and regional transport. Tucson is the second-largest city in Arizona and has received comparatively less attention than the most populated city of Phoenix despite experiencing elevated O₃ levels amid rapid population growth. This study provides a comprehensive 22 year analysis (2001–2022) of O₃ trends in Tucson using a combination of ground-based monitoring data, satellite observations, NEI emissions inventories, land cover classification and meteorological datasets. The findings reveal no statistically significant long-term trend in O₃ levels at northwest (NW), urban core, and south/southeast (S/SE) monitoring sites despite regulatory actions to reduce precursor levels. However, spatial differences persist with one S/SE site (Saguaro National Park) consistently exhibiting the highest O₃ concentrations and an urban core site (Rose Elementary) usually exhibiting the lowest values across all seasons. Satellite and surface-based data reveal a decline in NO₂ across the study period, in contrast to HCHO levels that show little long-term change, with a brief increase in 2020 likely linked to regional fire activity and higher temperatures, particularly in June. Consequently, FNR values (formaldehyde-to-NO₂ ratio) increased after 2005–2009, indicating a regional shift influenced by reductions in NO_x emissions, especially during fall/winter and spring. This shift helps explain the weakening of the weekend effect (i.e., higher weekend levels versus weekdays) over time and the emergence of the weekday effect earlier in the summer (June) in contrast to the late 1990s. Generalized additive model meteorology normalization suggests that 79% of the O₃ variability is attributed to interannual weather variability. FNR started to decline post-2020, suggesting changes in O₃ responsiveness to further NO₂ reductions, particularly in cooler months. These dynamics, along with recent fall/winter O₃ increases, highlight the complex, chemical regime-dependent response of O₃ to precursor changes. This study recommends improved VOC characterization to inform future air quality strategies in the region.

Decamethylcyclopentasiloxane (D₅), a widely used component of personal care products, readily partitions to the atmosphere where it can undergo oxidation, potentially forming secondary organic aerosol (SOA). The mechanism of aerosol formation, particularly at low OH exposure, remains highly uncertain, leaving open questions about the role of multigenerational chemistry, seed aerosol, and oxidation conditions. We performed chamber experiments of D₅ oxidation at low OH exposure to investigate SOA formation from D₅ (SiSOA) and the effect of seed aerosol using dry ammonium sulfate (AS) and dioctyl sebacate (DOS) seeds. We measured gas-phase D₅ and its oxidation products online using chemical ionization mass spectrometry and aerosol size and composition using scanning mobility particle sizing and aerosol mass spectrometry. In select experiments, gas- and particle-phase samples were collected for offline analysis by liquid chromatography with negative electrospray ionization and high-resolution mass spectrometry. The gas-phase products were similar for all experiments, composed primarily of 1-hydroxynonamethylcyclopentasiloxane, a first-generation oxidation product. For AS, the SiSOA was dominated by 1-hydroxynonamethylcyclopentasiloxane, with minor contributions from later-generation products. For DOS, the aerosol was composed of 1-hydroxynonamethylcyclopentasiloxane and an additional unidentified product, and the SiSOA yield was ∼3–10 times more than in AS experiments. For AS-seeded experiments, the timeseries of SiSOA evolution throughout the experiment suggests adsorption as the dominant partitioning mechanism, while for DOS-seeded experiments, absorption appears to be important. We estimated the saturation mass concentration (C*) of the SiSOA to be 1300 μg m⁻³. Overall, our work shows that the SiSOA formation mechanism depends on seed identity and that multiple oxidation steps will be required for significant SiSOA formation.

Light absorbing organic aerosol content, or brown carbon (BrC), affects climate through positive radiative forcing, may act as a photosensitizer in particle aging, and can directly play a role in the oxidative aging of organic aerosol. Wildfire emissions are a global source of BrC, and within wildfire emissions phenolic carbonyls (PhC) are some of the most photoreactive compounds emitted. Wildfire BrC components may have photochemical lifetimes of hours to days. Such a wide range in lifetimes makes detailed information on the products and mechanisms of BrC photochemistry critical in estimating effects of BrC on climate and aerosol chemistry. The aerosol chemical environment, particularly pH for aqueous aerosol, has strong effects on the reactivity of BrC, potentially altering absorption spectra and excited state reactivity. Various laboratory approximations of solar illumination have been used in studying the photochemistry of BrC compounds, making direct comparison between results difficult, and the relationship between chemical structure and reactivity of PhC is important for understanding and predicting BrC behavior and stability. In this work, aqueous photochemistry of six phenolic carbonyls (PhC) including coniferaldehyde (CA), 4-hydroxybenzaldehyde (4-HBA), 4-hydroxy-3,5-dimethylbenzaldehyde (DMBA), isovanillin (iVAN), vanillin (VAN), and syringaldehyde (SYR) was studied to elucidate relationships between structure, product formation, and photochemical mechanism. Using several narrow band UV-LEDs (295–400 nm), wavelength dependent quantum yields were calculated to allow direct comparison between photochemical experiments with laboratory irradiation sources and atmospheric actinic fluxes. Quantum yields were measured in acidic, air-saturated, aqueous solutions with pH = 2; conditions present in sulfate dominated aerosol or very acidic fog droplets. Computational results show that the electronic transitions leading to photochemical loss of PhC are nearly all π → π*, with conserved aspects of their electronic character. PhC photochemical quantum yields are concentration dependent, due to a direct reaction between triplet excited-state and ground-state PhC molecules, and maximum quantum yields of the range of structures studied span 0.05–2%. Wavelength dependent quantum yields are used to directly calculate the dependencies of photochemical loss on solar zenith angle (SZA).

Jakarta has experienced a particulate pollution problem in the last few decades. Our study aimed to investigate particulate spatial variability and identify the associated sources in more detail by measuring their composition in Jakarta at three sites in a north–south transect. We collected the mass using the Dichotomous Gent SFU and analysed the elemental concentration with a Smoke Stain Reflectometer and ED-XRF. Principal Component Analysis (PCA), correlation, and Conditional Bivariate Probability Function (CBPF) techniques were used to reveal the element's source attribution probabilities and their directional strengths. Black carbon (BC) and sulphur (S) were the major contributors to PM2.5 but not always to coarse particles. Motor vehicle fuel was a significant source of sulphur in most areas. Multiple-site data analyses reveal that in the city centre, traffic congestion was the main source of BC, while in South Jakarta, BC primarily originated from open waste/biomass burning. However, in North Jakarta, CBPF also suggested industrial coal and vessel diesel oil from the direction of the port as probable sulphur sources. While local sources dominated, the fine and coarse particle CBPFs demonstrated that some elements arrived from out-of-border sources during higher wind speed events. Long-distance anthropogenic and natural sources might include industries in the neighbouring cities and fumarolic emissions from the volcanic terrains in southern Jakarta. These results showed diverse sources and composition of PM in Jakarta's north-to-south transect. The large proportion of calm wind underscores the contrasted local sources' contribution to each site, leading to the apparent spatial and source variability within sites.

High incidences of crop residue burning (CRB) in Punjab and Haryana during October–November is one of the major causes of elevated PM_2.5 in Delhi National Capital Region (NCR). An estimation of precise contribution of CRB emissions to PM_2.5 levels in Delhi-NCR is hindered by uncertainties in meteorology, atmospheric chemistry and emissions, and lack of quality observations. We use continuous in situ observations of PM_2.5 from a wide area network of 30 stations during 16 October to 30 November (peak CRB season) of 2022, 2023 and 2024 under Aakash project. The WRF-Chem model is used for simulation of chemical compositions of the atmosphere over the northwest India region. We have incorporated five distinct CRB emission scenarios in addition to commonly used industrial and biological emissions for the simulations. Scenarios with and without CRB emissions from different regions were compared to assess their impacts on PM_2.5. The average CRB emission impact on PM_2.5 concentrations in Delhi-NCR during CRB season are estimated at 18%, 16% and 9% in 2022, 2023 and 2024, respectively. The low impact of CRB on PM_2.5 in 2024 could arise from a shift in CRB time to evening, which was not captured by existing emission inventories due to absence of satellite overpass in late evening. A shift to late evening CRB leads to very strong nighttime build-up of PM_2.5 due to emissions when the boundary layer is shallow. Inclusion of appropriate diurnal and synoptic variability in CRB emissions is important for simulating observed PM_2.5 levels and evaluation human health exposures.

The semiconductor-based Figaro Taguchi Gas Sensor (TGS) is sensitive to reducing gases, including methane. TGS methane response can be characterised by using the ratio between resistance in the presence of methane mole fraction ([CH₄]) enhancements and a reference resistance, representative of sampling under the same environmental conditions and with the same background gas composition, but at a reference [CH₄] level. Effects of environmental variables, including water mole fraction ([H₂O]), are expected to cancel in this resistance ratio, allowing for independent [CH₄] characterisation. This work seeks to examine the cause of changes in [CH₄] resistance ratio characterisation over time, including the hypothesis that resistance ratios are independent of [H₂O]. Precise gas blends were sampled under controlled conditions during sensor characterisation in synthetic air (SCS) tests, which showed [H₂O] to influence resistance ratio methane characterisation, although this effect's importance depends on the reference gas. Three SCS tests were also performed with gaps of 137 days followed by 295 days, all under similar environmental conditions and gas blends. [CH₄] resistance ratio response changed significantly during the first time gap, suggesting that something inherently changed sensor behaviour, but negligibly during the second time gap, suggesting that natural ageing is not otherwise a key driver of sensor behaviour. Additional SCS tests showed persistent changes in [CH₄] resistance ratio response following hydrogen sulphide exposure; this may have caused a change between controlled SCS tests conducted 137 days apart, although other atmospheric species may also have been responsible. This is an important consideration for laboratory testing and final sensor application. Meanwhile, power loss and sampling dry air negligibly affected a different TGS. In addition, a total of 147 successful sensor characterisation in ambient air (SCA) tests occurred irregularly over approximately 25 months, where small amounts of gas with a high [CH₄] were blended with ambient outdoor air. SCA tests showed a weaker correlation between time and [CH₄] response when restricted to the period covering the second (295-day) time window between the similar SCS tests. A residual observed SCA testing correlation with time could be attributed to changes in [H₂O] over time, supporting SCS testing conclusions.