Environmental science: atmospheres最新文献

The acidity of cloud droplets can vary with size due to differences in aerosol composition and cloud chemistry and differential soluble gas uptake. Chemical transport models (CTMs) often assume that all droplets have the same composition and therefore acidity. In this work, we use the PMCAMx CTM to simulate size-resolved cloud and fog droplet acidity over the US during a winter and a summer month as a function of altitude. Small droplets are assumed to form on the activated particles smaller than 2.5 μm and have an average diameter of 20 μm, whereas large droplets form on the coarse particles and have an average diameter of 30 μm. Our simulations show that large droplets are often more alkaline than small (up to 100% lower H⁺ concentrations) especially in regions influenced by dust. In areas with more acidic conditions, the difference in H⁺ concentrations between small and large droplets is smaller. The pH of droplets either decreases or increases with altitude, depending on the composition of the aerosol on which the droplets were formed. Comparison of the bulk and two-section size-resolved approaches indicates that current differences in aqueous-phase sulfate concentrations over the US are generally low and usually less than 20% at approximately 10 min intervals (the most frequent difference ranges from zero to 5%). Based on our results, bulk calculations can simulate current aerosol composition and droplet pH over the US with small discrepancies. This is due to reduced SO₂ emissions causing SO₂ levels in clouds to often fall below those of H₂O₂. Under these conditions the importance of the pH-dependent ozone sulfate production pathway is diminished. These findings are specific to the US and may not apply to regions with higher SO₂ emissions.

A Wideband Integrated Bioaerosol Sensor (WIBS) was used in conjunction with chemical tracer analysis for the first time during the 2022–2023 grass pollen season in Melbourne, Australia. WIBS detected continuous levels of bioaerosol throughout the campaign. From 18th November to 7th December 2022, fluorescent particles accounted for an average of 10% of total particles in number, corresponding to an estimated 0.18 μg m⁻³ PM_2.5 (14%) and 0.49 μg m⁻³ PM₁₀ (25%). Using mannitol as a chemical tracer, fungal spores were estimated to contribute to an average of 2% of PM_2.5 and 9% of PM₁₀ mass. Analysis of fructose in PM_2.5 as a marker for sub-pollen particles (SPPs) showed elevated concentrations during periods of hot and dry weather. There was negligible fructose observed with rain, suggesting that SPP production is not limited to water absorption processes or high relative humidity in Melbourne. Estimates of SPP mass via fructose corresponded to the equivalent of 1.1 m⁻³ intact pollen grains on average, 2% of the total pollen concentration, 7% of PM_2.5 fluorescent particle mass, and 1% of PM_2.5 mass. New hourly measured grass pollen data confirmed the timing and magnitude of grass pollen emissions in the Victorian Grass Pollen Emission Model (VGPEM) and captured the strong diurnal variation. Five grass pollen rupturing mechanisms using different meteorological drivers were tested against the WIBS and fructose measurements. Whilst the WIBS and model were not well correlated, likely due to the complex mixture of bioaerosols and low relative abundance of SPPs, the mechanical wind speed rupturing mechanism represented the fructose time series well. Conceptually, this suggests that mechanical rupturing describes SPP formation during hot and dry conditions in Melbourne. Long-term measurements in Melbourne will improve SPP formation process forecasting.

Accounting for nearly 5% of the global gross domestic product, the construction industry significantly contributes to environmental pollution, emitting a broad range of hazardous pollutants, including particulate matter (PM₁₀, PM_2.5), carbon monoxide (CO), nitrogen oxides (NO_x), volatile organic compounds (VOCs), benzene and polycyclic aromatic hydrocarbons (PAHs). Individuals spend approximately 90% of their time indoors, where the air quality is heavily influenced by construction and demolition (C&D) activities that are carried out within or adjacent to residences. Despite regulatory interventions in the early 21st century emphasizing the importance of indoor air quality (IAQ), the contribution of C&D activities to indoor pollution remains largely underexplored, particularly to seasonal variations, extended renovation periods, and the release of case-specific pollutants. This review bridges knowledge gaps by examining the correlation between construction activities, pollutant emissions, health risks, and the efficacy of existing regulations. Key investigations include the impact of infrastructural inefficiencies and improper ventilation on IAQ, seasonal pollutant variations, and the disproportionate exposure risks faced by vulnerable populations, such as women and workers. The literature suggests that prolonged exposure prompts sick-building syndrome and ailments such as compromised immunity, bronchial allergy, asthma, and lung cancer. A survey-based data collection and analysis were conducted to gather and refine residents' practical insights across India, contributing to the development of an IAQ index. This tailored index, ranging from 22 to 100, is designed for indoor environments, incorporating building-specific and occupancy-related factors. In the long term, the index can provide actionable insights for administrators and communities to mitigate IAQ risks effectively, promoting healthier indoor environments by providing a quantitative measure of the health risks associated with exposure to poor indoor air quality in the absence of a pollutant dataset. The study enables individual households to take measures to retrofit indoor spaces by upgrading to better-quality materials or modifying the design of the building to reduce health risks and improve air exchange.

Airborne cloud water measurements are examined in this study, with a focus on pH and interrelationships with influential species for three regions: the Northwest Atlantic (winter and summer 2020–2022), the West Pacific (summer 2019), and the Northeast Pacific (summers between 2011 and 2019). Northwest Atlantic results are categorized into three ways: data closer to the U.S. east coast for (i) winter, (ii) summer, and (iii) summertime measurements over Bermuda. The median pHs are as follows: Northwest Atlantic winter/summer = 4.83/4.96, Bermuda = 4.74, West Pacific = 5.17, and Northeast Pacific = 4.40. The regions exhibit median pH values of ∼4–6 across various altitude bins reaching as high as 6.8 km, with the overall minimum and maximum values being 2.92 and 7.58, respectively (both for the Northeast Pacific). Principal component analysis of species to predict pH shows that the most influential principal component is anthropogenic in nature. Machine leaning modeling suggests that the most effective combination of species to predict pH includes some subset of oxalate, non-sea salt Ca²⁺, NO₃⁻, non-sea salt SO₄²⁻, and methanesulfonate. These results demonstrate that cloud water acidity is relatively well constrained between a pH of 4 and 5.5 and that anthropogenic activities impact regional cloud water pH in the areas examined, with dust offsetting acidity at times.

Marine Cloud Brightening (MCB) is a proposed solar radiation management technique whereby the albedo of low-lying clouds is artificially enhanced by the addition of Cloud Condensation Nuclei (CCN). It is generally accepted that these would be produced by atomisation of seawater to produce droplets which form appropriately sized artificial sea spray aerosol (SSA). Despite extensive theoretical consideration of the MCB concept, progress in understanding how perturbations to complex cloud microphysical processes would evolve has been hampered by the technical inability to produce the very large numbers of SSA required. To facilitate the first phase of outdoor experimentation a single MCB station should be capable of producing around 10¹⁵ per s CCN. Effervescent nozzle technology has been posited as potentially capable of meeting these requirements. Here we describe an effervescent nozzle design that produces ∼1.73 × 10¹² per s SSA, with ∼71% of aerosols within a 30 to 1000 nm range (considered likely CCN), using ∼512 W of energy per nozzle. Producing 10¹⁵ CCN using this design would then require 814 nozzles and around 417 kW of energy, a demand that can be practically met on a research vessel. The nozzle described here is therefore sufficiently practical to facilitate outdoor in situ experimentation of MCB, enabling a new generation of perturbation experiments that directly probe cloud microphysical and radiative responses to aerosol.

The enforcement of global fuel sulfur content (FSC) regulations has significantly reduced SO₂ and particulate matter (PM) emissions from ships. However, the impact of the International Maritime Organization's (IMO) sulfur reduction policy on gaseous hydrocarbon emissions, including volatile and intermediate volatility organic compounds (VOCs/IVOCs), remains underexplored. In this study, a 4-stroke single cylinder marine engine was operated using marine gas oil (MGO, FSC = 0.01%) and low-sulfur heavy fuel oil (LS-HFO, FSC = 0.5%) across various engine loads, ranging from 20 kW to a maximum of 80 kW. Emissions were photochemically aged in the oxidation flow reactor “PEAR,” simulating an equivalent photochemical aging period from 1.4 ± 0.2 to 4.6 ± 0.8 days related to the OH· exposure. Emission factors (EFs) of all targeted VOCs/IVOCs varied significantly, ranging from 20.0 ± 2.5 to 180 ± 20 mg kWh⁻¹ and from 26.0 ± 11.0 to 280 ± 100 mg kWh⁻¹ from a high (80 kW) to low engine load (20 kW) for MGO and LS-HFO, respectively. Monoaromatics dominated total fresh emissions for MGO (64%) and LS-HFO (76%), followed by alkanes. Naphthalene and alkylated naphthalene content declined more than monoaromatic and alkane content, thus changing the VOC/IVOC emission pattern after photochemical aging. Estimated SOA from targeted VOC/IVOC precursors accounted for 41% of the measured secondary organic aerosol (SOA) for MGO, while a lower contribution (34%) was observed for LS-HFO at 20 kW engine load, highlighting the role of unmeasured VOCs/IVOCs in SOA formation. Expanding the research on the effects of atmospheric aging on marine emissions will offer valuable insights into this underexplored area.

Stratospheric aerosol injection (SAI) has been proposed as a geoengineering approach to temporarily offset global warming by increasing Earth's albedo. Here, we utilize light scattering calculations to examine how introducing solid aerosol particles into the stratosphere can enhance the Bond albedo, a key metric linking reflectivity directly to radiative forcing. We explore how particle size, refractive index (both real and imaginary components), and morphology (core–shell configurations) affect single scattering albedo, phase function, and the resulting integrated solar reflectivity. Our results show how the optimal aerosol size is governed by matching the wavelength of dipolar resonances with the peak of incoming solar spectral irradiance. We also examine how dispersion, absorption, and size distribution affect the extent of the Bond albedo enhancement and radiative forcing. Coated particles are also studied, and we find that very thin lower-index coatings can spoil albedo enhancement (e.g., layers of water or sulfuric acid that are only a few nanometres thick). Conversely, designing core–shell particles with a thin, higher-index shell and a low-density core can retain high reflectivity while substantially reducing particle mass and settling velocity, potentially extending the stratospheric residence time. The framework discussed here is versatile, readily extending to systems beyond homogeneous spherical particles, and it provides a straightforward means of comparing candidate SAI materials while guiding future laboratory studies, work on particle design, field experiments, and climate model parameterizations to assess the viability and risks of stratospheric aerosol geoengineering.

Wildfires impact global climate and public health by releasing gases and aerosols. Phthalic anhydride, a toxic chemical detected in wildfire smoke, has been primarily linked to the daytime oxidation of naphthalene and methylnaphthalenes. The recent report of phthalic anhydride in the nighttime oxidation of furan and furfural suggests that other heterocyclic volatile organic compounds (VOCs) may also act as potential precursors of phthalic anhydride through previously unrecognized pathways. This study presents the production of phthalic anhydride derived from the nighttime chemistry of 2-methylfuran, thiophenes, and methylpyrroles, with its mass fraction comprising ∼0.1–0.4% of the secondary organic aerosols (SOAs) derived from these heterocyclic VOCs. Phthalic anhydride is proposed to be produced via the cycloaddition of heterocyclic backbones. We estimate that the nighttime oxidation of heterocyclic VOCs may contribute variably to phthalic anhydride production across different fuel types, with a ∼30% contribution during wiregrass combustion. Overall, our findings highlight the need to further investigate the production of phthalic anhydride from these previously unrecognized precursors and pathways in wildfire smoke to better understand their atmospheric implications.

We present a “diagonal” Volatility Basis Set (dVBS) comparing gas-phase concentrations of oxygenated organic molecules (OOM) to their condensed-phase mass fractions. This permits closure of vapor concentrations with particle composition constrained by particle growth rates, allowing the contributions of quasi non-volatile condensation, equilibrium partitioning, and reactive uptake to be separated. The dVBS accommodates both equilibrium and dynamical (growth) conditions. Growth implies an association between gas and particle concentrations governed by a “condensation line” that is set by the particle growth rate, which fixes the total (excess) concentration of condensible vapors. The condensation line defines an infeasible region of high particle mass fraction and low gas concentration; under steady-state growth conditions, compounds cannot appear in this infeasible region without being formed by condensed-phase chemistry. We test the dVBS with observations from the CLOUD experiment at CERN using data from a FIGAERO I⁻ Chemical Ionization Mass Spectrometer measuring vapors directly and particle composition via temperature programmed desorption from a filter. A dVBS analysis finds that data from an α-pinene + O₃ run at 243 K are consistent with volatility driven condensation forming the large majority of particle mass, with no compounds clearly within the infeasible region.

The impact of poor air quality (AQ) on public health has long been recognised and considerable efforts have been made to improve it across the UK. The UK has a far reaching AQ monitoring network and this study summarises the evolution of UK AQ over the period 2015–2024, focusing on the pollutants NO₂, O₃ and PM_2.5 and exploring their drivers. Concentrations of NO₂ and PM_2.5 exhibit robust negative trends across the whole country while concentrations of O₃ increase. Comparing 2015–2016 to 2023–2024, the median number of days per year for which DEFRA AQ sites breached the WHO 2021 target decreased from 136 to 40 (−70%) for NO₂ and from 60 to 22 (−63%) for PM_2.5. This trend was mirrored in other AQ monitoring networks and highlights that, while progress is being made, acceptable levels of AQ are yet to be reached. Over the same period, median O₃ exceedances increased from 7 to 14 days per year. Nationwide analysis of diurnal variation in the pollutants and the use of airmass back trajectory clustering and statistical modelling for three locations – Reading, Sheffield and Glasgow – suggests that local traffic plays a dominant role in NO₂ pollution, PM_2.5 is influenced more by long range transport and O₃ increases are being driven in part by decreases in NO₂. From an AQ policy perspective, this suggests continued focus on traffic emissions will reduce NO₂, (inter)national rather than local efforts are most critical for PM_2.5 improvements, and reductions to VOC emissions must accompany NO₂ if further O₃ increases are to be avoided.