Aerosol Concentrations Research Articles

Phosphorus transitions driven by cyclone biparjoy linked middle east North Africa (MENA) and Indian Thar Desert dust storm pathways in Asia’s largest grassland

Phosphorus (P) is an important nutrient for terrestrial ecosystems like grassland and plays a critical role in influencing primary productivity and hence ecosystem dynamics. The deposition of airborne dust, particularly from arid and semiarid regions, has been recognised as a significant source of phosphorus input in distant ecosystems. The study area, the Banni grassland, is a semiarid ecosystem with a unique geological history that has experienced degradation for various natural and anthropogenic reasons. It is located in the arid tract of western India. Soil samples were collected from 10 × 10 km grid locations in the grassland before, 48 h after, and 20 days after a cyclonic storm, Biparjoy, which hit the region in June 2023. Statistical analyses (Shapiro‒Wilk normality and Kruskal–Wallis H test) were performed on the data to assess the differences in phosphorus concentrations in terms of PAC (Phosphorus Activation Coefficient) among the phases. To examine the long-range transport of dust-borne phosphorus and its subsequent deposition in the target grassland, we employed an interdisciplinary approach that integrated satellite imagery and ground-based measurements. Spatial and temporal variations in dust emissions were assessed using satellite remote sensing data, while ground truthing was performed for phosphorus content analysis using standard protocols. The aerosol data from MERRA-2 for the past 40 years were used to examine the relationships between aerosol concentrations and wind direction and speed. Our findings revealed that the Middle East, North Africa, and Thar Desert significantly contributed to phosphorus deposition in the target grassland during specific seasons. The SW cyclone ‘Biparjoy’, which followed the same track of aerosol loading (MENA), made landfall in this zone (June 16, 2023) and affected the P depositional patterns. The pre-cyclone, post-cyclone and 20 DAC (days after cyclone) had AP values of 15.15, 22.54 and 24.06, respectively. However, the TP values were 45.81 ± SE = 1.73, 60.95 ± SE = 1.39 and 61.98 ± SE = 1.40, respectively. The highest TP values were in phase 3 (20 DAC phase) (61.89 ± SE = 1.40). Similarly, the transformation of locked forms of P to bioavailable forms was coincidental with higher PSM (Phosphate Solubilising Microorganisms) in soil samples. Dust storms and other atmospheric circulation patterns were found to play pivotal roles in facilitating the long-range transport of phosphorus-laden dust particles from these source regions to the target grassland. Ultimately, our research contributes to the broader understanding of global nutrient cycling and land‒air interactions, enabling informed decision-making for the conservation and sustainable management of terrestrial ecosystems.

Transforming US agriculture for carbon removal with enhanced weathering.

Enhanced weathering (EW) with agriculture uses crushed silicate rocks to drive carbon dioxide removal (CDR)1,2. If widely adopted on farmlands, it could help achieve net-zero emissions by 20502-4. Here we show, with a detailed US state-specific carbon cycle analysis constrained by resource provision, that EW deployed on agricultural land could sequester 0.16-0.30 GtCO2 yr-1 by 2050, rising to 0.25-0.49 GtCO2 yr-1 by 2070. Geochemical assessment of rivers and oceans suggests effective transport of dissolved products from EW from soils, offering CDR on intergenerational timescales. Our analysis further indicates that EW may temporarily help lower ground-level ozone and concentrations of secondary aerosols in agricultural regions. Geospatially mapped CDR costs show heterogeneity across the USA, reflecting a combination of cropland distance from basalt source regions, timing of EW deployment and evolving CDR rates. CDR costs are highest in the first two decades before declining to about US$100-150 tCO2-1 by 2050, including for states that contribute most to total national CDR. Although EW cannot be a substitute for emission reductions, our assessment strengthens the case for EW as an overlooked practical innovation for helping the USA meet net-zero 2050 goals5,6. Public awareness of EW and equity impacts of EW deployment across the USA require further exploration7,8 and we note that mobilizing an EW industry at the necessary scale could take decades.

Direct observation of Arctic Sea salt aerosol production from blowing snow and modeling over a changing sea ice environment

In the polar regions, there is significant model bias in the number concentrations and seasonality of sea salt aerosol (SSA) due to the lack of understanding of aerosol sources associated with sea ice, which is hampering accurate climate forecasts at high latitudes. Recently, SSA originating from the sublimation of blowing snow has been directly observed to be an important source of aerosol particles in the Antarctic during winter/spring, validating a mechanism proposed a decade ago. Here, we report in situ observations of coarse aerosol production (particle diameter 0.5–20.0 µm) dominated by sea salt from blowing snow above sea ice during winter/spring in the Central Arctic during the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition from October 2019 to September 2020. Blowing snow conditions occurred 20–40% of the time during each of the months from December 2019 to April 2020, with a total of 26 blowing snow events. During blowing snow periods, coarse aerosol number concentrations increased often by an order of magnitude compared to no-blowing snow periods. Mass fractions of sodium chloride in sub-micron aerosol (particle diameter 0.01–0.625 µm) available during December 2019 and 10 m wind speed showed a significant correlation (R = 0.61, P < 0.05), indicating that much of the aerosol observed during storms is sea salt released by sublimating blowing snow. We use these observations to refine the current model parameterization by considering the spatial and temporal variability of atmospheric and sea ice conditions. Snow particle size distributions and snow salinities are expressed as a function of wind speed and snowpack depth, respectively, which can be easily implemented into climate models. Validation of the snow particle size distribution parameterization with previous polar winter observations showed agreement in the Arctic (N-ICE2015 cruise, March 2015) above the threshold for drift and blowing snow, but a negative bias in the Antarctic (Weddell Sea, June to August 2013). Updating the blowing snow mechanism in the chemical transport model p-TOMCAT with wind-dependent snow particle size distributions results in 14% more SSA produced and a slightly better correlation with MOSAiC observations of coarse aerosol (R = 0.28). Significant increases in aerosol number concentration due to blowing snow sublimation are calculated by as much as 70 cm−3 during the Antarctic winter and 50 cm−3 during the Arctic winter compared to a baseline simulation with no blowing snow. Thus, taking into account SSA from blowing snow above sea ice will be important to improve model predictions of polar aerosol and climate.

Emerging threats in Сentral Asia: Comparative characterization of organic and elemental carbon in ambient PM2.5 in urban cities of Kazakhstan.

This study (June 2022-July 2023) investigates the atmospheric concentrations of carbonaceous species, including organic carbon (OC) and elemental carbon (EC), in PM2.5 in two major cities in Kazakhstan. Samples were collected from two sites in Almaty (Seifullin and KazNU) and one in Astana. The results showed that Almaty had significantly higher annual average concentrations of OC (10.8 and 10.5μg/m3) and EC (1.68 and 1.87μg/m3) compared to Astana (OC: 7.1μg/m3, EC: 0.61μg/m3). Both cities exhibited pronounced seasonal variations, with significantly elevated concentrations (1.5-3.4 times for OC, 2.1-4.8 times for EC) during the heating season compared to the non-heating season. This indicates a significant influence of coal and biomass combustion for heating on carbonaceous aerosol concentrations. Both cities' OC/EC ratios varied widely (2.6-39.4), showing strong positive correlations (0.61-0.94) across all seasons except summer, suggesting a common primary emission source. Primary organic carbon dominated OC levels in winter (71-74%), whereas secondary organic carbon contributed significantly to OC concentrations in summer (43-50%). Higher OC-EC concentrations correlated with lower atmospheric visibility values. The OC-EC contributions to the total light extinction coefficient were estimated to be 15.3-15.9% for Almaty and 12.0% for Astana stations.

Interactions between Dust Aerosols and the Ultra-high Atmospheric Boundary Layer: Case study of vertical observation over the Taklimakan Desert, China

A deep atmospheric boundary layer (ABL) with a height of up to 4,000–6,000 m can develop over the Taklimakan Desert (TD). Nevertheless, the deep ABL in the TD was only studied for clean days. To date, the observational evidence concerning the interaction between the ultra-high ABL and dust aerosols over the TD remains scarce. In May 2022, we conducted the inaugural observational particle-sounding experiment in the TD, selecting representative cases of light and heavy dust days. The results captured a distinctive stratified structure of the daytime ABL induced by dust aerosols characterized by an ultra-thick residual layer (RL) in the afternoon. On heavy dust days, the daytime ABL was divided into convective boundary layer (CBL), capping inversion layer (CIL), RL and residual capping inversion layer (RCIL). Dust aerosols exerted a warming effect in the atmosphere reaching a maximum of about 1.0 K/day at the top of the dust aerosol layer and causing a temperature inversion. A CIL about 1,000 m occurred between the CBL and the RL, which acted as a barrier, restraining CBL development and hindering dust aerosol transport. Furthermore, a deeper stable boundary layer on heavy dust days at night was observed. A unique vertical structure of nocturnal dust aerosol concentrations peaks of 477μg/m3 was also observed in the deep RL at 1800-2600 m. The radiation effects of dust aerosols strengthened and weakened the stability of the RL above and below the dust layer, respectively. The study provided vertical observational evidence of the impact of dust aerosols on the deep ABL structure, thus contributing to a more profound comprehension of aerosol–radiation interactions over the desert arid region.

Multiple eco-regions contribute to the seasonal cycle of Antarctic aerosol size distributions

Abstract. In order to reduce the uncertainty of aerosol radiative forcing in global climate models, we need to better understand natural aerosol sources which are important to constrain the current and pre-industrial climate. Here, we analyse particle number size distributions (PNSDs) collected during a year (2015) across four coastal and inland Antarctic research bases (Halley, Marambio, Dome C and King Sejong). We utilise k-means cluster analysis to separate the PNSD data into six main categories. “Nucleation” and “bursting” PNSDs occur 28 %–48 % of the time between sites, most commonly at the coastal sites of Marambio and King Sejong where air masses mostly come from the west and travel over extensive regions of sea ice, marginal ice and open ocean and likely arise from new particle formation. “Aitken high”, “Aitken low” and “bimodal” PNSDs occur 37 %–68 % of the time, most commonly at Dome C on the Antarctic Plateau, and likely arise from atmospheric transport and ageing from aerosol originating likely in both the coastal boundary layer and free troposphere. “Pristine” PNSDs with low aerosol concentrations occur 12 %–45 % of the time, most commonly at Halley, located at low altitudes and far from the coastal melting ice and influenced by air masses from the west. Not only the sea spray primary aerosols and gas to particle secondary aerosol sources, but also the different air masses impacting the research stations should be kept in mind when deliberating upon different aerosol precursor sources across research stations. We infer that both primary and secondary components from pelagic and sympagic regions strongly contribute to the annual seasonal cycle of Antarctic aerosols. Our simultaneous aerosol measurements stress the importance of the variation in atmospheric biogeochemistry across the Antarctic region.

Evaluation of aerosol loading and its relationship with geopotential height in Nigeria’s Guinea Coast

Climate variability and atmospheric changes significantly affect weather patterns and human activities. Aerosols impact the Earth's climate by influencing cloud formation, scattering radiation, and cooling the planet. However, aerosols, like black carbon, absorb and reemit radiation, contributing to global warming. This study aims to assess aerosol optical depth (AOD) over Nigeria's Guinea Coast, compare aerosol loading across the region, examine the relationship between aerosol loading and geopotential height, and explore the impact of meteorological variables on aerosol levels. AOD data were sourced from MODIS, while geopotential height and meteorological data was obtained from MERRA-2. The study found significant aerosol loading during the dry season, particularly along the coastal region (Lagos, Warri, and Port Harcourt), and lower AOD during the wet season. Geopotential height values were higher during the wet season, especially at 1000-hPa and 850-hPa. A positive correlation was found between AOD and geopotential height. Wind speeds were higher in the north and along the coast, with specific humidity at 1000-hPa directly correlating with geopotential height and inversely with wind speed. The study also showed that the annual AOD distribution mirrors geopotential height patterns at 1000-hPa, with higher values in southern Nigeria. In conclusion, aerosol loading is higher during the dry season, particularly in coastal regions and at lower atmospheric levels. The study highlights how seasonal changes and geographical factors influence aerosol distribution. It also shows that geopotential height strongly affects aerosol concentration, with higher heights linked to increased AOD. This underscores the importance of surface-level aerosols for human health, agriculture, and visibility, and suggests that geopotential height influences where aerosol loading is highest.

Exploration of aerosol-precipitation relationships under different climate regimes in China

ABSTRACT Aerosols influence cloud and precipitation formation through Aerosol-Radiation Interaction and Aerosol-Cloud Interaction, thereby influencing rainfall patterns. Our study analyzed the relationship between aerosols and precipitation in China by remote-sensing observations, focusing on both precipitation magnitude and microphysical characteristics. The aerosol data were obtained from the second Modern-Era Retrospective analysis for Research and Applications (MERRA-2), the precipitation data were sourced from Integrated Multi-satellitE Retrieval for Global Precipitation Measurement (GPM-IMERG) and rainfall microphysical data were collected from the GPM Dual-Frequency Precipitation Radar (GPM-DPR). The total aerosol and five types of aerosols (two natural types and three anthropogenic types) were analyzed in relation to precipitation over the period 2015–2020. Aerosols were categorized into “clean” and “polluted” groups based on their concentrations. The spatial distribution of average rainfall for the clean and polluted groups was analyzed on three time scales (annual, summer, and winter). The results indicated that different types of aerosols present varying effects on rainfall, with natural aerosols exhibiting higher average rainfall in “clean” conditions, while anthropogenic aerosols demonstrate higher average rainfall in “polluted” conditions, especially in humid areas. Additionally, we observed that aerosol concentrations can modify rainfall microphysics, affecting the size and concentration of raindrops. By comparing D m (the mass-weighted diameter of a raindrop) and N w (the concentration parameter) under different aerosol conditions, it was found that D m was significantly larger in summer than winter and in polluted than clean conditions. N w exhibited slightly higher values in clean conditions. Overall, our findings suggest that enhanced aerosol concentrations intensify rainfall and modify rainfall microphysics, which may be useful in further investigating the principles of how aerosols affect precipitation.

A long-term decline in downward surface solar radiation

Abstract Downward surface solar radiation (DSSR) is critical for the Earth system. It is well-known that DSSR over land fluctuated on decadal timescales in the past. By utilizing a combination of station observations and the latest CMIP6 simulations, here we show that DSSR has a global consistent decline during 1959–2014, with comparable contributions from greenhouse gases (GHG) and anthropogenic aerosols. The role of GHGs is even more important in the satellite period. The contribution from GHGs comes through rising temperature, which reduces the DSSR by increased water vapor but is partly offset by reduced cloud. Future changes of DSSR are heavily dependent on climate change scenarios, which can be predicted well by global mean temperature (GMST) and aerosol concentrations. The sharp aerosol reduction and weak temperature rise in the SSP245/SSP126 scenarios will limit or stop the long-term decline of DSSR with a brighter future.

Nontarget screening of a Siberian ice core reveals changes in the pre-industrial to industrial organic aerosol composition.

Glaciers serve as natural archives for reconstructing past changes of atmospheric aerosol concentration and composition. While most ice-core studies have focused on inorganic species, organic compounds, which can constitute up to 90% of the submicrometer aerosol mass, have been largely overlooked. To our knowledge, this study presents the first nontarget screening record of secondary organic aerosol species preserved in a Belukha ice core (Siberia, Russian Federation), ranging from the pre-industrial to the industrial period (1800-1980 CE). We identified a total of 398 molecules, primarily polar and low-volatile compounds. Since the 1950s, the atmospheric aerosol composition has changed, with the appearance of organic molecules, including nitrogen-containing compounds, deriving from enhanced atmospheric reactions with anthropogenic NOx, or direct emissions. In addition, there was a significant increase in the oxygen-to-carbon ratio (+3%) and the average carbon oxidation state (+18%) of the detected molecules compared to the pre-industrial period, suggesting an increased oxidative capacity of the atmosphere.

Characteristics of salt dust aerosols and their transport implications in the Aral Sea

Central Asia is an ecologically fragile arid zone and a typical mixed salt‒sand region. The socioeconomic and ecological problems attributed to the shrinking of the Aral Sea in Central Asia are notable concerns within the international community. In this study, the characteristics of salt dust aerosols from the Aral Sea were analysed to explore their interannual variation characteristics and analyse the spatial and temporal distributions of salt dust sources and transport and dispersion pathways. The results revealed that high concentrations of salt dust aerosols were concentrated around the Aral Sea and Lake Sarekamesh. The range and intensity of salt dust aerosols were less than those of dust aerosols. Salt dust events occurred frequently in spring and less frequently in autumn and winter. The occurrence frequency and impact range of salt dust aerosols from 2008 to 2012 were significantly lower than those during the previous period. From 2013 to 2018, the salt dust sources originated largely on the western side of the North Aral Sea. The spatial autocorrelation of salt dust aerosols was high and characterized by significant agglomeration, with significant changes in cold spot and hotspot regions. Salt dust in the Aral Sea region affects mainly the Kazakhstan region in spring, and it more notably affects Russia in winter. The results of this study increase the understanding of the spatial and temporal variability in salt dust aerosols within the arid zone of Central Asia and lay a foundation for the study of the impacts of salt dust aerosols on the climate system and ecological environment in arid zones.

The establishment of blue-sky index: how to quantify the aerosol optical impacts on sky color

Abstract Color of the sky serves as a direct indicator of haze, while also exerting substantial influence on human physiological and psychological well-being, as well as the overall environmental scenery. However, quantifying color changes is quite challenging. This research develops a quantitative approach for evaluating the influence of atmospheric aerosol pollution on the appearance of the sky. We first calculated the influence of atmospheric aerosols on the sky’s diffuse radiation, which is the source of sky color. Then, we mapped the diffuse radiation onto a perceptually uniform color space to quantify alterations in sky color. The results reveal that the relationship between aerosol concentration and sky color change follows a logarithmic-like distribution: the higher the concentration, the weaker the change in sky color per unit increase in aerosol concentration. Consequently, during the early phases of air pollution control implementation, there may be minimal observable changes in the color of the sky. However, as these measures are further enforced, a discernible bluing effect on the sky will become evident. Based on the quantification of the change of sky color, a blue-sky index (BSI) was established. We find that concurrent with improvements in air quality resulting from emission reduction measures, the BSI has significantly decreased in recent years in China. This trend indicates an increase in the frequency of blue-sky occurrences.

Unprecedented East Siberian wildfires intensify Arctic snow darkening through enhanced poleward transport of black carbon.

Summer Arctic black carbon (BC) predominantly originates from boreal wildfires, significantly contributing to Arctic warming. This study examined the impact of MODIS-detected extensive East Siberian wildfires from 2019 to 2021 on Arctic BC and the associated radiative effects using GEOS-Chem and SNICAR simulations. During these years, Arctic surface BC aerosol concentrations rose to 46ngm-3, 43ngm-3, and 59ngm-3, nearly doubling levels from the low-fire year of 2022. East Siberian wildfires accounted for 62%, 75%, and 79% of elevated BC levels in 2019, 2020, and 2021, respectively. These wildfires also increased BC deposition on snow and sea ice, particularly in the Laptev and East Siberian Seas. The resulting snow contamination (30.6±5.15ngg-1, 15.4±1.29ngg-1, and 33.8±5.24ngg-1) reduced surface snow albedo, increasing summer Arctic radiative forcing over snow and sea ice by +1.38±0.65Wm-2, +0.70±0.20Wm-2, and+1.46±0.73Wm-2 in 2019, 2020, and 2021, respectively. As climate warming intensifies, more frequent extreme wildfires in East Siberia could further amplify Arctic snow darkening, potentially accelerating Arctic warming.

Potential impacts of marine fuel regulations on an Arctic stratocumulus case and its radiative response

Abstract. Increased surface warming over the Arctic triggered by increased greenhouse gas concentrations and feedback processes in the climate system has been causing a steady decline in sea-ice extent and thickness. With the retreating sea ice, shipping activity will likely increase in the future, driven by economic activity and the potential for realizing time and fuel savings from using shorter trade routes. Moreover, over the last decade, the global shipping sector has been subject to regulatory changes that affect the physicochemical properties of exhaust particles. International regulations aiming to reduce SOx and particulate matter (PM) emissions mandate ships to burn fuels with reduced sulfur content or, alternatively, use wet scrubbing as an exhaust aftertreatment when using fuels with sulfur contents exceeding regulatory limits. Compliance measures affect the physicochemical properties of exhaust particles and their cloud condensation nucleus (CCN) activity in different ways, with the potential to have both direct and indirect impacts on atmospheric processes such as the formation and lifetime of clouds. Given the relatively pristine Arctic environment, ship exhaust particle emissions could cause a large perturbation to natural baseline Arctic aerosol concentrations. Low-level stratiform mixed-phase clouds cover large areas of the Arctic region and play an important role in the regional energy budget. Results from laboratory marine engine measurements, which investigated the impact of fuel sulfur content (FSC) reduction and wet scrubbing on exhaust particle properties, motivate the use of large-eddy simulations to further investigate how such particles may influence the micro- and macrophysical properties of a stratiform mixed-phase cloud case observed during the Arctic Summer Cloud Ocean Study campaign. Simulations with diagnostic ice crystal number concentrations revealed that enhancement of ship exhaust particles predominantly affected the liquid-phase properties of the cloud and led to decreased liquid surface precipitation, increased cloud albedo, and increased longwave surface warming. The magnitude of the impact strongly depended on ship exhaust particle concentration, hygroscopicity, and size, where the effect of particle size dominated the impact of hygroscopicity. While low-FSC exhaust particles were mostly observed to affect cloud properties at exhaust particle concentrations of 1000 cm−3, exhaust wet scrubbing already led to significant changes at concentrations of 100 cm−3. Additional simulations with the cloud ice water path increased from ≈ 5.5 to ≈ 9.3 g m−2 show more-muted responses to ship exhaust perturbations but revealed that exhaust perturbations may even lead to a slight radiative cooling effect depending on the microphysical state of the cloud. The regional impact of shipping activity on Arctic cloud properties may, therefore, strongly depend on ship fuel type, whether ships utilize wet scrubbers, and ambient thermodynamic conditions that determine prevailing cloud properties.

Long-term spatiotemporal features of aerosol optical characteristics and relative humidity in China’s offshore areas

ABSTRACT Marine aerosols are crucial for ocean–atmosphere interactions. However, there is a lack of analysis on the long-term aerosol optical characteristics and relative humidity (RH) based on large-scale ocean regions. This paper addresses this issue by analyzing the spatiotemporal variations of aerosols in China’s offshore waters from 2007 to 2022 using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and European Centre of Medium-range Weather Forecasts Reanalysis v.5 (ERA5) data. The results show that in the sea area, the aerosol backscatter coefficient at 532 nm and extinction coefficient at 532 nm increase with increasing RH; the aerosol depolarization ratio decreases with increasing RH. The optical properties of aerosols are generally lower in summer, while they fluctuate with rising RH in other seasons. Notably, the values recorded in 2014–2019 were markedly lower than those in 2007–2013. Nevertheless, from 2020 to 2022, the proportion of aerosol types remained largely stable compared to that of 2014–2019, suggesting a negligible impact of the COVID-19 pandemic on emissions, but the near-shore waters’ aerosol optical properties were more sensitive to minor changes than those of far-off waters. After dividing the China’s offshore waters, the overall optical properties of aerosols decreased in order of the Bohai Sea and Yellow Sea, the East China Sea, and the South China Sea, due to the proportion of marine aerosols increase toward the south. After dividing the altitude layer in the sea area, within the range of 0–7 km, the higher the altitude, the less oceanic aerosols and the more terrestrial aerosols. The aerosol depolarization ratio rises, while the aerosol backscatter coefficient at 532 nm and extinction coefficient at 532 nm alternate downwards. We speculate this is linked to the steep decline in total aerosol content as altitude rises. Our results could provide theoretical references for further deepening the understanding of aerosol generation mechanisms in China’s offshore waters.

Indoor air concentrations of PM2.5 quartz fiber filter-collected ionic PFAS and emissions to outdoor air: findings from the IPA campaign.

Per- and polyfluoroalkyl substances (PFAS) are prevalent in consumer products used indoors. However, few measurements of ionic PFAS exist for indoor air. We analyzed samples collected on PM2.5 quartz fiber filters (QFFs) in 11 North Carolina homes 1-3 times in living rooms (two QFFs in series), and immediately outside each home (single QFF), for 26 ionic PFAS as part of the 9 months Indoor PFAS Assessment (IPA) Campaign. All targeted PFAS, except for PFDS and 8:2 monoPAP, were detected indoors. PFBA, PFHpA, PFHxA, PFOA, PFOS, and 6:2 diPAP were detected in >50% of indoor samples. PFHxA, PFOA, and PFOS had the highest detection frequency (DF = 80%; medians = 0.5-0.7 pg m-3), while median PFBA concentrations (3.6 pg m-3; DF = 67%) were highest indoors. Residential indoor air concentrations (sum of measured PFAS) were, on average, 3.4 times higher than residential outdoor air concentrations, and an order of magnitude higher than regional background concentrations. Indoor-to-outdoor emission rate estimates suggest that emissions from single unit homes could be a meaningful contributor to PFBA, PFOA, and PFOS emissions in populated areas far from major point sources. Backup QFFs were observed to adsorb some targeted PFAS from the gas-phase, making reported values upper-bounds for particle-phase and lower-bounds for total air (gas plus particle) concentrations. We found that higher concentrations of carbonaceous aerosol were associated with a shift in partitioning of short chain PFCAs and long chain PFSAs toward the particle phase.

Spatio-temporal analysis of extreme air pollution and risk assessment.

Extreme air pollution poses global health and environmental threats, necessitating robust policy interventions. This study first analyses the surface mass concentration of major aerosols (such as black carbon, organic carbon, dust, sea salts, and sulphates) to estimate global PM2.5 concentrations from 1980 to 2023. The developed model-estimated PM2.5 database was validated against data from 526 cities worldwide, showing strong accuracy, with RMSE, r, and R2 values of 7.47μg/m³, 0.87, and 0.75, respectively. The motivation arises from the need to understand whether recent pollution increases are driven by rising emissions or natural variability, given the significant impacts on life and property. To assess both short-and long-term pollution trends, magnitudes, and risks, we proposed twelve novel extreme pollution indices, which comprehensively characterize the spatial and temporal variations in pollution. The highest PM2.5 concentrations were observed in regions near the Saharan Desert, reaching up to 90,000μg/m³. However, significant PM2.5TOT (total pollution) concentrations were also found in the Indo-Gangetic Plain (IGP) and eastern China, ranging from 20,000 to 40,000μg/m³. Persistent pollution burdens North Africa for approximately 350 days annually, while the IGP and eastern China experience extreme pollution for over 200 days yearly. Other pollution indices highlight the intensity and frequency of pollution in regions such as North Africa, IGP, Eastern Russia, Western USA, and Eastern China, revealing critical regional air quality challenges. Our analysis identifies cities in low-income and middle-income countries, such as New Delhi, Lahore, Dhaka, and Dammam, as being at extreme risk scores above 90 out of 100. Meanwhile, cities like Ghaziabad, Chongqing, Kolkata, Mumbai, and East London fall into the high-risk category, scoring between 60 and 80. Conversely, most cities in the EU, USA, and Canada are at very low risk, a result of the effective implementation of strategic air pollution norms and policies. The study promotes a phased approach for low- and middle-income regions, emphasizing achievable air quality standards, low-cost monitoring, targeted interventions, urban greening, public awareness, and innovative financing for improvements.

Tidal currents and atmospheric inorganic nitrogen contribute to diurnal variation of dissolved nutrients and chlorophyll a concentrations in Mirs Bay, Hong Kong

The surface layer of central Mirs Bay exhibits high chlorophyll a concentrations despite having lower dissolved nitrate levels than other parts of Hong Kong. It is hypothesised that tidal currents and atmospheric inorganic nitrogen bring in nutrients that could be rapidly consumed by primary producers. We conducted fieldwork campaigns in September and December 2022 to test these hypotheses. Surface seawater was obtained hourly in September and half-hourly in December, and concentrations of chlorophyll a and dissolved nutrients were determined. Nitrogen content of aerosols was measured by a newly-developed online analyser. In September, we observed peaks in dissolved nutrients and chlorophyll a occurred after receding tides, which may have transported nutrients from the surrounding land. In December, there were anomalous nutrient and chlorophyll peaks that could not be attributed to low tides. These peaks may be responses to the overnight deposition of atmospheric nitrogen. Our dataset thus supports our hypothesis and highlights the need for further investigation to quantify the impact of both tidal currents and atmospheric deposition on carbon export to and oxygen consumption in bottom waters. The rapid changes observed could also be due to tidal currents transporting nutrients and chlorophyll a. Follow-up studies can repeat the fieldwork using Lagrangian (i.e. following tidal currents) instead of Eulerian (i.e. static sampling points) sampling. Moreover, current results indicate strong diurnal variability in chlorophyll a and suggest that existing monitoring efforts may be biased, depending on their timing during the day and/or the season.

Antibiotic-resistant bacteria aerosol in a Caribbean coastal city: Pre- and post- COVID-19 lockdown.

This study assessed the prevalence and spatial distribution of viable ultrafine and fine antibiotic-resistant bacteria aerosols (ARB) in the Metropolitan Area of Barranquilla, Colombia, pre- and post-lockdown (September 2019 to December 2020). Samples were systematically collected from urban, suburban, and rural sites using a six-stage viable cascade impactor. We employed logistic regression and Bayesian Neural Network Classifiers to analyze meteorological variables' influence on antibiotic resistance persistence. The lockdown led to a significant decrease (76%) in overall bacterial aerosol concentrations, likely due to reduced human activity. The most significant reduction (82%) was observed at Peace Square. Bacillus cereus was the most prevalent species, showing high concentrations at all sampling sites. Other species, like Leifsonia aquatica and Staphylococcus lentus, were linked to wastewater effluents and agricultural activities. Despite the overall decrease in bacterial aerosols, antibiotic-resistant bacteria remained high, particularly in highly impacted urban areas like the Barranquilla Riverwalk. Bacillus cereus exhibited resistance to multiple antibiotics, including commonly used ones like Ampicillin and Penicillin G. Resistance to newer antibiotics like Vancomycin was rare. Peace Square, a high-traffic urban area, showed elevated resistance rates in the deeper respiratory regions compared to other locations. Our findings indicate that while overall concentration levels decreased, the threat of antibiotic resistance in bacterial bioaerosols persists, emphasizing the need for continuous monitoring and targeted public health interventions in urban areas.

Association of spring thermal forcing anomalies in the Tibetan Plateau with dust aerosol changes over the Taklamakan Desert.

The Tibetan Plateau (TP) is significantly influencing the climate and environmental evolution regionally and globally. Adjacent to the northwestern TP, the Taklimakan Desert (TD) experiences the unique pattern of dust aerosol variations due to the deep basin terrain. However, systematic studies on how TP climate change affects TD dust aerosol variations are lacking. This study employs MERRA-2 and ERA5 reanalysis data (1991-2020) to investigate the impact of springtime TP thermal forcing on TD dust aerosol. Results indicate that the interannual variation of dust column mass densities over the TD showed an increasing trend over 1991-2020, with a significant increase in the northern TD, where the maximum value exceeded 9.51mgm-2 per year. Thermal forcing strengthening on the northwestern TP are positively correlated with dust column mass density variations in the northern TD, while negatively correlated in the southern TD. Further comprehensive analyses indicate that strong northwestern TP thermal forcing has increased dust aerosol concentrations in northern TD, with a maximum 14mgm-3 increase at 700hPa, while decreasing them in the southern part. During strong SNTP-Q1 years, anticyclonic anomalies, strong updrafts, and the blocking effect of the Tian Shan Mountains, combined with high temperatures, result in dust aerosols suspended in the atmosphere over the northern TD. In contrast, during weak SNTP-Q1 years, cyclonic anomalies, strong downdrafts, and the large topography of the TP, along with inversion temperatures, contribute to dust aerosol accumulation in the southern TD. This study elucidates the mechanism of TP thermal forcing on TD dust aerosol variations, enhancing understanding of its effects on environmental and climatic changes in the TD and Central Asia.