Aerosol Emissions Research Articles

Glaciation of liquid clouds, snowfall, and reduced cloud cover at industrial aerosol hot spots.

The ability of anthropogenic aerosols to freeze supercooled cloud droplets remains debated. In this work, we present observational evidence for the glaciation of supercooled liquid-water clouds at industrial aerosol hot spots at temperatures between -10° and -24°C. Compared with the nearby liquid-water clouds, shortwave reflectance was reduced by 14% and longwave radiance was increased by 4% in the glaciation-affected regions. There was an 8% reduction in cloud cover and an 18% reduction in cloud optical thickness. Additionally, daily glaciation-induced snowfall accumulations reached 15 millimeters. Glaciation events downwind of industrial aerosol hot spots indicate that anthropogenic aerosols likely serve as ice-nucleating particles. However, rare glaciation events downwind of nuclear power plants indicate that factors other than aerosol emissions may also play a role in the observed glaciation events.

Indian Ocean temperature anomalies modulate the interannual variability of springtime smoke aerosols over the Indochina Peninsula

Abstract Smoke aerosols released through frequent springtime fire activity over the Indochina Peninsula (ICP) seriously affect regional air quality, climate, and human health. However, the mechanisms driving the interannual variability of these smoke aerosols are not well understood. By analyzing multi-source historical (1980–2020) smoke aerosols and meteorological reanalysis data, we explore the response of springtime smoke aerosol changes over the ICP to the interannual variability of the Indian Ocean (IO) sea-surface temperature (SST). Our findings show a positive correlation between the variability of springtime smoke aerosol loading and the preceding winter Southeast IO (SEIO) SST anomalies. Warmer SEIO SST tends to weaken the trans-equatorial flow (TEF) and the local Hadley circulation. This weakening of the TEF impede cyclones development in the Bay of Bengal (BOB), thereby reducing southwest water vapor transport. Simultaneously, enhanced westerly winds over the northern BOB are blocked by the northwestern mountains of ICP. These winds converge and rise on the windward slopes, while descending on the leeward side with diminished humidity. Collectively, these dynamics lead to drier and hotter local meteorological conditions that favored fire-induced smoke aerosol emissions. Our findings highlight the role of the SEIO in regulating smoke aerosol variability and provide a scientific basis for developing strategies to manage smoke aerosol emissions over the ICP.

Constraining light dependency in modeled emissions through comparison to observed biogenic volatile organic compound (BVOC) concentrations in a southeastern US forest

Abstract. Climate change will bring about changes in meteorological and ecological factors that are currently used in global-scale models to calculate biogenic emissions. By comparing long-term datasets of biogenic compounds to modeled emissions, this work seeks to improve understanding of these models and their driving factors. We compare speciated biogenic volatile organic compound (BVOC) measurements at the Virginia Forest Research Laboratory located in Fluvanna County, VA, USA, for the year 2020 with emissions estimated by the Model of Emissions of Gases and Aerosols from Nature version 3.2 (MEGANv3.2). The emissions were subjected to oxidation in a 0-D box model (F0AM v4.3) to generate time series of modeled concentrations. We find that default light-dependent fractions (LDFs) in the emissions model do not accurately represent observed temporal variability in regional observations. Some monoterpenes with a default light dependence are better represented using light-independent emissions throughout the year (LDFα-pinene=0, as opposed to 0.6), while others are best represented using a seasonally or temporally dependent light dependence. For example, limonene has the highest correlation between modeled and measured concentrations using an LDF =0 for January through April and roughly 0.74–0.97 in the summer months, in contrast to the default value of 0.4. The monoterpenes β-thujene, sabinene, and γ-terpinene similarly have an LDF that varies throughout the year, with light-dependent behavior in summer, while camphene and α-fenchene follow light-independent behavior throughout the year. Simulations of most compounds are consistently underpredicted in the winter months compared to observed concentrations. In contrast, day-to-day variability in the concentrations during summer months are relatively well captured using the coupled emissions–chemistry model constrained by regional concentrations of NOX and O3.

An updated aerosol simulation in the Community Earth System Model (v2.1.3): dust and marine aerosol emissions and secondary organic aerosol formation

Abstract. Aerosols constitute important substance components of the Earth's atmosphere and have a profound influence on climate dynamics, radiative properties, and biogeochemical processes. Here we introduce updated emission schemes for dust, sea-salt, and marine primary organic aerosols (MPOA), as well as augmented secondary organic aerosol (SOA) formation pathways within the Community Earth System Model (CESM; version 2.1.3). The modified dust emission scheme shifts the original hotspot-like dust emission to a more continuous distribution, improving the dust aerosol optical depth (DAOD) simulations at stations in north Africa and central Asia. This update also reduces dust residence time from 4.1 to 1.6 d, enhancing concentration simulations downwind of dust source regions. For sea-salt emissions, we incorporate an updated sea surface temperature (SST) modulation and introduce a relative-humidity-dependent correction factor for sea-salt particle size, with SST having a significantly larger impact on sea-salt emissions (16.1 %) compared to the minor effect of humidity (−0.3 %). We then extend our modelling to incorporate emissions of marine primary organic aerosols (MPOA) as mixed externally with sea-salt aerosols, coupled offline with the ocean component Parallel Ocean Program (POP2). The results underscore the substantial influence of phytoplankton diversity on MPOA emissions, with 148 % variability simulated among different phytoplankton types, highlighting the role of biological variability in aerosol modelling. Furthermore, we refine the model's chemical mechanisms by including the irreversible aqueous uptake of dicarbonyl compounds as a new pathway for SOA formation, contributing an additional 37 % to surface SOA concentrations. These improvements enrich the ability of the CESM to use intricate linkages between different components of the Earth system, thereby enabling a more comprehensive description of natural aerosol emissions, chemical processes, and their impacts.

Characteristics and ingredients of disposable 'Elfbar' e-cigarettes sold in the United States and the United Kingdom.

As of 2023, Elfbar remains the most popular brand of disposable e-cigarette available in the United States (US) and United Kingdom (UK), with similar flavor options in both countries. At the time of this study, 5% nicotine Elfbar BC5000 was the only version available in the US, whereas 2% Elfbar 600 was the most popular in the UK. This study measured differences in nicotine content and form, aerosol emissions and flavoring chemicals in the US and UK Elfbar products. A convenience sample of eight Elfbar devices sold in the US and UK, consisting of two Elfbar models with four identical flavor options (Peach Ice, Strawberry Banana, Strawberry Ice and Strawberry Kiwi) purchased between December 2022 and February 2023, were laboratory tested. We measured nicotine concentration, form and total content. We also determined aerosol emissions and estimated the nicotine dose delivery per puff. We identified solvents and flavoring chemicals in these products. Elfbar products within the same country had similar nicotine content, concentration, form and solvents, but they differed in flavoring chemicals. US Elfbar contained, on average, higher volume (mean ± standard deviation = 6.5 ± 0.5 versus 1.8 ± 0.3ml) of nicotine solution with a higher concentration (41.8 ± 2.3 versus 19.7 ± 1.2mg/ml) than the UK Elfbar. An estimated dose of nicotine delivered per puff was four times higher from US Elfbar than UK Elfbar. There were differences in the type and amount of flavoring chemicals used in US and UK Elfbars, including a higher concentration of a synthetic coolant WS-23 in US Elfbar than in UK Elfbar (17.8 ± 1.5 versus 12.9 ± 5.4mg/ml). Because the amount of nicotine found in the US Elfbar e-cigarettes is equivalent to that found in eight UK Elfbar e-cigarettes, people who use Elfbar sold in the US have access to much more nicotine from a single device than those who use Elfbar sold in the United Kingdom.

Displacement Factors for Aerosol Emissions From Alternative Forest Biomass Use

ABSTRACTSubstituting alternative materials and energy sources with forest biomass can cause significant environmental consequences, such as alteration in the released emissions which can be described by displacement factors (DFs). Until now, DFs of wood‐based materials have included greenhouse gas (GHG) emissions and have been associated with lower fossil and process‐based emissions than non‐wood counterparts. In addition to GHGs, aerosols released in combustion processes, for example, alter radiative forcing in the atmosphere and consequently have an influence on climate. In this study, the objective was to quantify the changes in the most important aerosol emission components for cases when wood‐based materials and energy were used to replace the production of high‐density polyethylene (HDPE) plastic, common fossil‐based construction materials (concrete, steel and brick), non‐wood textile materials and energy produced by fossil fuels and peat. For this reason, we expanded the DF calculations to include aerosol emissions of total suspended particles (TSP), respirable particulate matter (PM10), fine particles (PM2.5), black carbon (BC), nitrogen oxides (NOx), sulphur dioxide (SO2) and non‐methane volatile organic compounds (NMVOCs) based on the embodied energies of materials and energy sources. The DFs for cardboard implied a decrease in BC, SO2 and NMVOC emissions but an increase in the other emission components. DFs for sawn wood mainly indicated higher emissions of both particles and gaseous emissions compared to non‐wood counterparts. DFs for wood‐based textiles demonstrated increased particle emissions and reduced gaseous emissions. DFs for energy biomass mainly implied an increase in emissions, especially if biomass was combusted in small‐scale appliances. Our main conclusion highlights the critical need to thoroughly assess how using forest biomass affects aerosol emissions. This improved understanding of the aerosol emissions of the forestry sector is crucial for a comprehensive evaluation of the climate and health implications associated with forest biomass use.

Winter haze amplification by aerosol hygroscopic growth over eastern Indo- Gangetic Plain

Frequent occurrences of widespread winter haze over Northern India largely appear to originate from exceedingly high concentrations of fine particulate matter from anthropogenic emissions. However, the underlying mechanisms driving winter haze in Northern India are not well understood. This study employed a synergy of satellite and reanalysis data from 2006 to 2021 to assess the role of hygroscopic growth of aerosol optical depth in winter haze over the eastern Indo-Gangetic Plain. A method has been developed to extract dry aerosol optical depth from ambient aerosol optical depth to elucidate the origin of winter haze. About 31% of severe haze episodes (aerosol optical depth > 0.85) occurring under ambient humidity conditions decrease to below 5% for dry conditions, indicating the critical role of particle hygroscopic growth. The change in radiative forcing at the top of the atmosphere due to hygroscopic growth is relatively small compared to that at the surface and in the atmosphere, indicating enhanced atmospheric warming. The ubiquitous winter haze over the eastern Indo-Gangetic Plain is exacerbated by hygroscopic growth under high anthropogenic aerosol emissions, further aggravated through aerosol-radiation feedback. These results will be valuable in devising haze forecasts, implementing effective mitigation policies, and representing aerosol hygroscopicity in climate models.

Increased Asian Sulfate Aerosol Emissions Remarkably Enhance Sahel Summer Precipitation

AbstractObservational evidence shows that Sahel summer precipitation has experienced a considerable increase since the 1980s, coinciding with significant diverging trends of increased sulfate emissions in Asia and decreased emissions in Europe (dipole pattern of aerosols between Asia and Europe). The decrease in European sulfate aerosols has substantial effects on the Sahel summer precipitation increase, but the corresponding effect of increased Asian sulfate is unknown. Multi‐model simulations in the Precipitation Driver and Response Model Intercomparison Project (PDRMIP) show, compared to decreased European aerosols, that increased Asian aerosols similarly enhance the Sahel summer precipitation but with different large‐scale atmospheric circulation changes. Further analysis of the Sixth Coupled Model Intercomparison Project (CMIP6) simulations under historical attribution and various emission scenarios reinforces the results about the climate impacts of anthropogenic aerosols and suggests that in future scenarios with strong international cooperation and rapid climate mitigations (SSP2‐45), the Sahel drought will be intensified likely due to the decline in Asian aerosol emissions. Our results suggest that Asian anthropogenic aerosols are likely a non‐negligible driver of the recent recovery in Sahel precipitation amounts.

Effect of Regional Anthropogenic Aerosols on Tropical Cyclone Frequency of Occurrence

AbstractPrevious studies have highlighted the distinct impacts of anthropogenic aerosols from the Western and Eastern Hemispheres on past multi‐decadal changes in tropical cyclone frequency of occurrence (TCF). However, the detailed effect of subregional aerosol variations remained unclear. Using idealized simulations with a dynamical climate model, this study reveals that reduced aerosol emissions from Europe and the U.S. since 1980 may have equally contributed to increased TCF over the North Atlantic, with Europe playing a major role in the decreased TCF in the South Indian Ocean and the U.S. contributing to the decrease in TCF in the South Pacific. Additionally, increased aerosol emissions from India since 1980 may have played a major role in decreasing TCF over the western North Pacific compared to increased emissions from China. TCFs are projected to decrease for most global tropics toward the end of this century due to the dominant effect of increasing greenhouse gases.

Design and Characterization of a New Quartz Smog Chamber System for Studying the Atmospheric Effects of Vehicle Emissions on Plateaus

Since the 1960s, smog chambers have been an important tool for studying air pollution, and many indoor and outdoor smog chambers have been developed both domestically and internationally. However, all of these chambers are located at altitudes below 1500 meters, only simulating atmospheric conditions in low-altitude plains. Moreover, most are made of polytetrafluoroethylene (PTFE), resulting in a higher wall deposition effect. To simulate the evolution of atmospheric pollution in high-altitude regions, we developed the world's highest-altitude quartz smog chamber, located in Kunming at an elevation of 1900 meters. The chamber is a 3.375m³ cube constructed from 5mm quartz glass and features controlled temperature (0°C to 40°C) and relative humidity (2%-95%). We conducted a comprehensive characterization of the chamber, including tests for temperature and humidity stability, mixing stability, pressure resistance and sealing, light intensity measurement and environmental light matching, and background pollutant and wall loss assessments. The characterization results indicate excellent performance in simulating sunlight and controlling background pollutants. The NO2 photolysis rate is adjustable, ranging from 2.03×10⁻³s⁻1 to 5.87×10⁻³s⁻1. Under dry conditions, after 6 hours of photooxidation, the detected O3 formation rate was approximately 1.05 ppb/h, with a particulate mass concentration around 0.12 μg/m³. The reactor withstands pressures exceeding 1.5 bar, and at this pressure, the leak rate was measured at 1.1‰. Validation using the toluene-NO₂ system showed that indoor mixing reached equilibrium in about four minutes. The wall loss rate for SWFU-HAP particles at 25°C and RH <10% was 0.066 h⁻1, which is 70% lower compared to other chambers, while at RH = 50%, the wall loss rate was 0.137 h⁻1. These results demonstrate the superior performance of our system, meeting the high standards required for high-altitude vehicle exhaust aerosol emissions research and the investigation of the formation mechanisms of vehicle exhaust in high-altitude atmospheric environments.

An improved representation of aerosol in the ECMWF IFS-COMPO 49R1 through the integration of EQSAM4Climv12 – a first attempt at simulating aerosol acidity

Abstract. The atmospheric composition forecasting system used to produce the Copernicus Atmosphere Monitoring Service (CAMS) forecasts of global aerosol and trace gas distributions, the Integrated Forecasting System (IFS-COMPO), undergoes periodic upgrades. In this study we describe the development of the future operational cycle 49R1 and focus on the implementation of the thermodynamical model EQSAM4Clim version 12, which represents gas–aerosol partitioning processes for the nitric acid–nitrate and ammonia–ammonium couples and computes diagnostic aerosol, cloud, and precipitation pH values at the global scale. This information on aerosol acidity influences the simulated tropospheric chemistry processes associated with aqueous-phase chemistry and wet deposition. The other updates of cycle 49R1 concern wet deposition, sea-salt aerosol emissions, dust optics, and size distribution used for the calculation of sulfate aerosol optics. The implementation of EQSAM4Clim significantly improves the partitioning of reactive nitrogen compounds, decreasing surface concentrations of both nitrate and ammonium in the particulate phase, which reduces PM2.5 biases for Europe, the US, and China, especially during summertime. For aerosol optical depth there is generally a decrease in the simulated wintertime biases and for some regions an increase in the summertime bias. Improvements in the simulated Ångström exponent are noted for almost all regions, resulting in generally good agreement with observations. The diagnostic aerosol and precipitation pH calculated by EQSAM4Clim have been compared to ground observations and published simulation results. For precipitation pH, the annual mean values show relatively good agreement with the regional observational datasets, while for aerosol pH the simulated values over continents are quite close to those simulated by ISORROPIA II. The use of aerosol acidity has a relatively smaller impact on the aqueous-phase production of sulfate compared to the changes in gas-to-particle partitioning induced by the use of EQSAM4Clim.

Opinion: How will advances in aerosol science inform our understanding of the health impacts of outdoor particulate pollution?

Abstract. Air pollution, characterized by high levels of particulate matter (PM), poses the greatest environmental threat to human health, causing an estimated 7 million deaths annually and accounting for 5 % of the global gross domestic product (GDP). While the health impacts of PM are influenced by the toxicity of its individual chemical constituents, the mortality burden of PM is solely based on its total mass concentration. This is because of a lack of large-scale, high-resolution data on PM chemical composition, needed for epidemiological assessments. Identifying which PM constituents are harmful to health has been the “holy grail” of atmospheric science since the landmark 1993 study on six US cities established a definitive link between PM and mortality. Ever since, atmospheric scientists have focused on understanding aerosol composition, emission sources, and formation pathways, while longitudinal epidemiological studies have required individual-level exposure data, employing land use regression models for the prediction of exposures at fine resolutions. In this opinion article, we argue that the time has come to shift the focus towards incorporating PM chemical composition into epidemiological health assessments, laying the foundation for the development of new regulatory metrics. This shift will enable the creation of targeted guidelines and subsequent regulations, prioritizing mitigation efforts against the most harmful anthropogenic emissions. Central to this shift is the availability of global, long-term, high-resolution data on PM chemical composition that are obtained through field observations and modelling outputs. In the article, we underscore key milestones within aerosol science that have been integral for advancing this foundational shift. Specifically, we examine emerging modelling tools for estimating exposure to individual PM components, present the type of ambient observations needed for model developments, identify key gaps in our fundamental understanding of emissions and their atmospheric transformation, and propose advancing cross-disciplinary collaboration between aerosol scientists and epidemiologists to understand the health impacts of individual PM components. We contend that aerosol science has now reached a pivotal moment in elucidating the differential health impacts of PM components, representing a first step towards their incorporation into air quality guidelines.

Accelerated surface brightening in China: The decisive role of reduced anthropogenic aerosol emissions

A profound comprehension of the key determinants behind the fluctuations in surface solar radiation (SSR) over decadal timescales is essential for advancing the fields of energy meteorology, climatology, and solar resources. While there is a general agreement among prior research on the significant impact of aerosols on SSR, a granular understanding of the specific influence that varying aerosol types exert on SSR remains elusive. This investigation delves into the respective impacts of aerosols and cloud radiative effects across China, utilizing data from the Clouds and the Earth's Radiant Energy System (CERES). It further dissects the distinct impacts of different aerosol types on the decadal-scale variations in SSR, employing spectral aerosol optical depths derived from the MODIS aerosol products. The findings reveal a predominantly positive trend in SSR, ranging from 1.5 to 2.5 W/m2/yr between the years 2011 and 2022 for the majority of China's regions. However, certain areas within Northeast and Western China exhibit a decline in SSR exceeding −1 W/m2/yr. Notably, in Eastern China, a downward trend in aerosol radiative effect is observed, with a pronounced reduction of approximately −2 W/m2/yr noted specifically during the summer in Northern China. The study infers that the reduction in urban industrial emissions and biomass burning aerosols is linked to the acceleration of the brightening phenomenon in China. Our results underscore that stringent regulation of anthropogenic emissions could yield dual benefits: environmental amelioration and an upsurge in solar resource. These insights merit serious contemplation in the formulation of future policy and decision-making frameworks.

Emission Factors for Biochar Production from Various Biomass Types in Flame Curtain Kilns

Simple and low-cost flame curtain (“Kon-Tiki”) kilns are currently the preferred biochar technology for smallholder farmers in the tropics. While gas and aerosol emissions have been documented for woody feedstocks (twigs and leaves) with varying moisture contents, there is a lack of data on emissions from other types of feedstocks. This study aims to document the gas and aerosol emissions for common non-woody feedstocks and to compare emissions from finely grained, high-lignin feedstock (coffee husk) with those from coarser, low-lignin feedstocks (maize cobs, grass, sesame stems). Throughout each pyrolysis cycle, all carbon-containing gases and NOx were monitored using hand-held sensitive instruments equipped with internal pumps. Carbon balances were used to establish emission factors in grams per kilogram of biochar. The resulting methane emissions were nearly zero (&lt;5.5 g/kg biochar) for the pyrolysis of three dry (~10% moisture) maize cobs, grass, and a 1:1 mixture of grass and woody twigs. For sesame stems, methane was detected in only two distinct spikes during the pyrolysis cycle. Carbon monoxide (CO) and aerosol (Total Suspended Particles, TSP) emissions were recorded at levels similar to earlier data for dry twigs, while nitrogen oxide (NOx) emissions were negligible. In contrast, the pyrolysis of finely grained coffee husks generated significant methane and aerosol emissions, indicating that technologies other than flame curtain kilns are more suitable for finely grained feedstocks. The emission results from this study suggest that certification of biochar made from dry maize, sesame, and grass biomass using low-tech pyrolysis should be encouraged. Meanwhile, more advanced systems with syngas combustion are needed to sufficiently reduce CO, CH4, and aerosol emissions for the pyrolysis of finely grained biomasses such as rice, coffee, and nut husks. The reported data should aid overarching life-cycle analyses of the integration of biochar practice in climate-smart agriculture and facilitate carbon credit certification for tropical smallholders.

Bioaerosols and VOC emissions from landfill leachate treatment processes: Regional differences and health risks

The landfill leachate treatment process (LLTP) is a crucial anthropogenic source of bioaerosols and volatile organic compounds (VOCs) with potential environmental impacts and on-site health risks to plant workers. However, factors influencing microbial aerosol and VOC emissions remain poorly understood. We sampled and analyzed bioaerosols and VOCs in two process sections (oxidation ditch [OD] and reverse osmosis membrane [RO]) of LLTPs in northern (NLF) and southern (SLF) China. Bioaerosol concentrations were highest in OD, and particle size predominantly ranged from 0.654.7 µm. Microbial community analysis revealed distinct differences between geographical locations and process sections, with 332 genera identified. Genera such as Paenibacillus, Bacillus, and Pseudomonas were prevalent at all sampling sites. Oxygen-containing compounds (e.g., acetophenone and propionic acid) were the dominant VOCs, particularly in SLF-OD. Network analysis showed complex interactions, with Sphingomonas and ketones playing central roles in microbial and VOC communities, respectively. Partial least squares (PLS) modeling indicated a significant correlation between bioaerosols and VOCs. Specific microorganisms, such as TK10, Adhaeribacter, and Lachnospiraceae, were major contributors to emissions of hazardous VOCs (e.g., toluene and styrene). The ozone-generation potential and olfactory effect of the OD were significantly higher than those of RO; and those of SLF were higher than those of NLF. Health risk assessments indicated potential chronic toxicity and cancer risks associated with VOC exposure to specific compounds, such as trichloroethylene. Bioaerosol exposure occurred primarily through inhalation, particularly in male workers. This study establishes a theoretical foundation for the prevention and control of air-phase pollutant risks associated with LLTPs.

Исследование методов и современных технических решений очистки аэрозольных выбросов промышленности

The analysis and characterization of aerosol emissions into the atmosphere are given, the ways of formation of primary and secondary aerosols are considered. The process of atmospheric aging of aerosols, which has a negative impact on the environment, is considered. The functional links between aerosol emissions, their source and impact on climate and public health are presented. The possible influence of the reactions of liquid and solid aerosol particles on the properties of atmospheric air is considered. The main methods of purification of industrial aerosol emissions are considered: adsorption purification, thermal and catalytic neutralization, chemisorption and absorption purification. The ways of increasing the efficiency of adsorption processes, for example, the separation of adsorbent in the apparatus, are analyzed. The essence of the process of thermal neutralization of gas mixtures is described, it is established that thermal installations based on the direct combustion method work more efficiently when combining thermal and catalytic neutralization methods, designs of combined equipment are presented, and ways to increase the intensity of the apparatus are considered. The process of gas purification based on the absorption process is considered. It is determined that absorption plants for cleaning gases from harmful components are the most effective and efficient due to the high level of technical implementation of the process. The development and improvement of the main absorber equipment is aimed at achieving maximum cleaning efficiency with an optimal pressure drop that determines energy consumption. The analysis shows the negative impact of natural and anthropogenic aerosols on the environment. In order to correctly solve the problem, information on the sources, composition and properties of aerosols is needed to select the most effective and economically profitable cleaning method, which will help reduce the anthropogenic load on the atmosphere.

Multi-year gradient measurements of sea spray fluxes over the Baltic Sea and the North Atlantic Ocean

Abstract. Ship-based measurements of sea spray aerosol (SSA) gradient fluxes in the size range of 0.5–47 µm in diameter were conducted between 2009–2017 in both the Baltic Sea and the North Atlantic Ocean. Measured total SSA fluxes varied between 8.9 × 103 ± 6.8 × 105 m−2 s−1 for the Baltic Sea and 1.0 × 104 ± 105 m−2 s−1 for the Atlantic Ocean. The analysis uncovered a significant decrease (by a factor of 2.2 in the wind speed range of 10.5–14.5 m s−1) in SSA fluxes, with chlorophyll a (chl a) concentration higher than 3.5 mg m−3 in the Baltic Sea area. We found statistically significant correlations for both regions of interest between SSA fluxes and various environmental factors, including wind speed, wind acceleration, wave age, significant wave height, and wave Reynolds number. Our findings indicate that higher chl a concentrations are associated with reduced SSA fluxes at higher wind speeds in the Baltic Sea, while the influence of wave age showed higher aerosol emissions in the Baltic Sea for younger waves compared to the Atlantic Ocean. These insights underscore the complex interplay between biological activity and physical dynamics in regulating SSA emissions. Additionally, in both measurement regions, we observed weak correlations between SSA fluxes and air and water temperature and between SSA fluxes and atmospheric stability. Comparing the Baltic Sea and the North Atlantic, we noted distinct emission behaviors, with higher emissions in the Baltic Sea at low wave age values compared to the Atlantic Ocean. This study represents the first comparative analysis of SSA flux measurements using the same methodology in these contrasting marine environments.

In-situ online investigation of biogenic volatile organic compounds emissions from tropical rainforests in Hainan, China

Biogenic volatile organic compounds (BVOCs) emitted by tropical plants represent a significant proportion of global emissions, but the in-situ BVOC measurements in tropical rainforests are extremely sparse. Herein, a vehicle-mounted mobile monitoring system was developed for in-situ online investigations of BVOC emissions from thirty representative tree species in the tropical rainforests of Hainan Island, southern China. The results showed that monoterpenes were the primary BVOCs emitted from most broadleaf trees. Isoprene, sabinene, γ-terpinene and β-ocimene were the most abundant BVOCs. Localized canopy-scale emission factors (EFs) exhibited notable discrepancies with the defaults in the Model of Emissions of Gases and Aerosols from Nature (MEGAN), specifically with isoprene EFs being slightly lower than the model, while the EFs for monoterpenes and sesquiterpenes were 1 to 27 times higher than those in MEGAN. The BVOC emission inventory for the predominant mature forest species in Hainan Island in 2023 was further estimated to be 244.43 Gg C·yr−1, with isoprene and monoterpenes accounting for 74 % and 16 %, respectively. Additionally, unimodal monthly variation patterns were revealed, with BVOC emissions peaked in July (30.08 Gg C·yr−1) and bottomed in January (8.84 Gg C·yr−1). This study demonstrates the potential and versatility of the applied mobile platform for in-situ online measurements of plant volatiles. Our findings provide important data support for reducing uncertainties in BVOC emission estimations in tropical rainforests and for evaluating their health benefits in the context of forest therapy.

Interdecadal Springtime Aerosol Increase in the North Indian Ocean Observed From the Satellite AVHRR Instrument

AbstractA 38‐year aerosol optical thickness (AOT) satellite product from the Advanced Very High‐Resolution Radiometer (AVHRR) is used to investigate the aerosol variabilities in the North Indian Ocean (NIO). A dipolar mode with a notable meridional contrast between the equatorial and northern NIO is revealed by the second mode of Empirical Orthogonal Function (EOF) analysis with a sharp rise over the Arabian Sea (AS) and Bay of Bengal (BoB) since 2002. Our results show that the aerosol dipolar variation is primarily modulated by an El Niño–Southern Oscillation (ENSO) during 1983–2001 (ID1) and by a warm phase of Atlantic Multi‐decadal Oscillation (AMO) during 2002–2020 (ID2), leading to a dry‐and‐warming condition spanning the coasts of East Africa, the Arabian Peninsula (AP), and South Asia (SA) that favors increasing aerosol emission and a longer life cycle in the upstream regions. A warm phase of the AMO tends to excite an anomalous cyclone in western Siberia and reinforces anticyclonic circulation in the Tibetan Plateau. Correlation analyses between the second EOF mode time series and other parameters in ID1 and ID2 show that an interannual dry‐and‐warming condition over the AP–SA is associated with a noticeable north‐south contrast of convection between the equatorial NIO and AP–SA in ID1. But in ID2, a zonal contrast of anomalous convective activities between the AP–SA and the BoB‐South China Sea is dominant, partially due to the warming AMO, which aids the development of anticyclonic cells over the TP and the strengthened subtropical westerly jet streams.

A Distinct Role for Aerosol and GHG Forcing in Historical CMIP6 Evapotranspiration Trends

AbstractEvapotranspiration (ET) is crucial for the global water balance, plant growth, and freshwater availability. It connects the surface water balance with surface energy fluxes, making its accurate representation vital for climate projections. However, global climate models (GCMs) struggle with ET representation due to resolution limitations and simplified depictions of soil, plant, and atmosphere interactions. Simulated future changes in ET are uncertain, and the role of driving processes remain unclear. Here, we explore the utility of a simple and interpretable method to disentangle these varying drivers. We investigate the sensitivity of JJA ET to different atmospheric variables through simple linear models predicting ET from atmospheric variables only. The model consistently yields good results across GCMs or forcing scenarios. We find that GCMs have shown strong decreases and subsequent increases in ET over the historical period, related to changes in net surface radiation. For future climate projections, decreases in water availability compete with higher available surface radiation, making future projections uncertain. Single forcing GCM realizations show that historical ET trends in densely populated regions have been more influenced by aerosol emissions than greenhouse gases. Finally, we investigate which atmospheric variables explain most short‐term (year‐to‐year) and long‐term (decadal) changes. While water availability may be the most important driver of short‐term variability, for certain regions, radiation trends dominate long‐term forcing. This paper leverages a simple approach to provide a comprehensive and understandable view into recent and future changes in ET, reconciling the evidence provided by more complex case studies.