Aerosol Reduction Research Articles

Cloud and Aerosol Impacts on the Radiation Budget over China from 2000 to 2023

Aerosols and clouds influence Earth’s radiative energy budget, but their regional radiative impacts remain insufficiently understood. This study investigates the spatial distribution patterns and long-term trends of radiative fluxes over China from March 2000 to February 2023 using CERES-SYN data. Notable decreasing trends in the net radiative fluxes over China at the top of the atmosphere (−0.38 W m−2 year−1) and the surface (−0.35 W m−2 year−1) during the study period have been observed. Cloud properties from CERES-SYN and aerosol properties from MERRA-2 are used to assess the impacts of aerosols and clouds on radiative flux variations. Results show that aerosols are the primary drivers of radiative flux variations across China, while cloud changes exert notable but regionally dependent influences. In southern China, reductions in black carbon and organic carbon aerosols substantially influence radiative flux variations, along with contributions from changes in mid-high, mid-low, and low clouds. In northern China, decreases in dust and organic carbon aerosols primarily drive radiative flux trends. Over the Tibetan Plateau, variations in mid-high clouds predominantly affect radiative flux changes. In Xinjiang and Inner Mongolia, fluctuations in high, mid-high, and mid-low clouds, along with dust and sulfate aerosols, jointly contribute to the radiative flux variations, although the overall impacts remain relatively small.

Reduction in Organic Aerosol from Coal Combustion is Partially Offset by Enhanced Secondary Formation during the Beijing Coal Burning Ban.

A coal ban policy in northern China during winter 2017 enforced a switch from coal to gas or electricity for residential heating, providing a unique opportunity to study the effect of reduced coal combustion emissions on organic aerosol (OA). This study explores OA composition, sources, and atmospheric transformations in Beijing before and during the coal ban using online aerosol chemical speciation monitor (ACSM) and offline 14C measurements. Four primary factors (hydrocarbon-like, cooking, biomass burning, coal combustion OA) and one secondary factor (oxygenated OA, OOA) were resolved from ACSM. In response to the coal ban, OA concentrations generally decreased, but coal combustion OA decreased most strongly, consistent with the decreased fossil carbon contributions to OA (67 ± 3% before vs 55 ± 4% during the ban). Concurrently, the OOA fraction increased from 45 to 72%, due to a larger decrease in concentrations of primary OA (POA; 59-88%) compared to OOA (34%), highlighting the enhanced secondary aerosol formation during the coal ban period. This aligns with the 14C evidence of higher water-soluble carbon in fossil OA (which has mostly secondary sources). During the coal ban period, Ox concentrations doubled and were positively correlated with the OOA fraction, highlighting strong photochemical OA production. The results show that the reduction of POA from stringent clean air actions is partially offset by enhanced secondary OA formation.

Long-term trends in aerosol properties derived from AERONET measurements

Abstract. Over the past 2 decades, remarkable changes in aerosol concentrations and compositions have been observed worldwide, especially over developing countries, potentially resulting in considerable changes in aerosol properties. The Aerosol Robotic Network (AERONET) offers high-precision measurements of aerosol optical parameters over about 1700 stations globally, many of which have long-term measurements for 1 or more decades. Here we use AERONET Level 2.0 quality-assured measurements to investigate long-term aerosol optical depth (AOD) and Ångström exponent (AE) trends and quality-controlled Level 1.5 inversion products to analyse trends in absorption aerosol optical depth (AAOD) and single scattering albedo (SSA) at stations with long-term records. We also classify the aerosol properties in these sites into six types and analyse the trends in each type. Results reveal decreases in AOD over the majority of the stations, except for northern India and the Arabian Peninsula, where AOD increased. AE (computed from the AOD within the range of 440–870 nm) decreased in Europe, eastern North America, and the Middle East but increased over South Asia and western North America. The decreased AE over Europe and eastern North America is likely due to decreased fine-mode anthropogenic aerosols, whereas that over the Arabian Peninsula is attributed to increased dust activity. Conversely, increased AE over northern India is probably attributed to increased anthropogenic emissions and decreased dust loading. Most stations in Europe, North America, East Asia, and South Asia exhibit negative trends in AAOD, whereas Solar_Village in the Arabian Peninsula has positive trends. SSA at most stations increases and exhibits opposite trends to AAOD but with several stations in North America and central Europe showing decreased SSA values. Trend analysis of different aerosol types further reveals the changes in different aerosol components that are related to AOD, AE, AAOD, and SSA trends. The reductions in aerosols in eastern North America mainly result from non-absorbing species. Reductions in both fine-mode absorbing species and non-absorbing aerosols are found over Europe and East Asia, but the reduction in absorbing species is stronger than that of non-absorbing species. Increased aerosols in Kanpur over northern India should be mainly comprised of fine-mode scattering species, whereas those in Solar_Village over the Arabian Peninsula are mainly dust. The majority of stations exhibit consistent monotonic trends across different seasons for these parameters.

Impact of improved air quality during complete and partial lockdowns on surface energetics and atmospheric boundary layer.

Impact of improved air quality during complete and partial lockdowns on surface energetics and atmospheric boundary layer.

Disentangling the contributions of anthropogenic climate change, greenhouse gases, and aerosols to heat-related mortality in Great Britain: a climate change impact attribution study.

Anthropogenic aerosols are a critical contributor to climate change and their net cooling effects can partially counter the warming effects of greenhouse gases, but they are rarely considered in health impact attribution studies of climate change. The aim of this study was to attribute heat-related deaths in Great Britain to anthropogenic climate change and individual forcings of greenhouse gases and aerosols. Using a special suite of climate simulations, past and future heat-related deaths in Great Britain attributable to the relative contributions of anthropogenic greenhouse gas and aerosol forcings were estimated under the Shared Socioeconomic Pathway SSP2-4.5. Empirical confidence intervals were quantified combining uncertainties from climate models and health risk functions. Emergence of heat-related mortality associated with anthropogenic climate change was partially counteracted by the cooling effects of aerosols, with the time of emergence being approximately four decades later compared with the greenhouse gas-only simulation. We estimate that around 700 annual heat-related deaths during 1961-1980 were masked by the cooling effects of aerosols. There was a sharp increase in heat-deaths between 1980 and 2020 due to the combined effects of greenhouse gas increases and large aerosol reductions. By the end of the 21st century, a 2-6-fold increase in heat-related deaths due to greenhouse gases is projected, with a negligible counteracting contribution of aerosols. In addition to greenhouse gases, the potential contributions of aerosols should be considered when assessing climate change risks and mitigation pathways. This is crucial due to their opposing temperature effects, diverging future emission trajectories, and varying geographical scales. Separate attribution of climate change impacts to the global effects of greenhouse gases and local effects of aerosols can enhance transparency and equity, and can inform loss and damage funding models. Such impact attribution assessments can help to optimise health co-benefits and prevent unintended negative consequences of environmental policies on heat-related and air pollution-related health outcomes. Health Protection Research Unit in Environmental Change and Health, National Institute for Health and Care Research.

Aerosol Decline Accelerates the Increasing Extreme Precipitation in China

AbstractExtreme precipitation is becoming more intense and frequent. The increasing trends in extreme precipitation in China in warm season related to changes in aerosols and greenhouse gases (GHGs) are investigated using observations, reanalysis data and model simulations. A significant accelerating increase in extreme precipitation occurred around 2010, with the trend in accumulated extreme rainfall amount (R95pTOT) increasing from 2.88 mm per decade during 2000–2010 to 22.88 mm per decade during 2010–2023. The sudden acceleration of the increasing extreme precipitation is largely attributed to the reverse in aerosol trends associated with China’s clean air actions, which affects extreme precipitation through perturbing cloud microphysics and atmospheric dynamics, accounting for half of the change in R95pTOT trends. Future aerosol reduction to achieve carbon neutrality is shown to continue to intensify the extreme precipitation, which overweighs the effect induced by GHGs, highlighting the importance of aerosol changes in modulating future climate and weather extremes.

Factors Affecting Reduction of Infectious Aerosols by Far-UVC and Portable HEPA Air Cleaners

Factors Affecting Reduction of Infectious Aerosols by Far-UVC and Portable HEPA Air Cleaners

The short-term comprehensive impact of the phase-out of global coal combustion on air pollution and climate change.

The short-term comprehensive impact of the phase-out of global coal combustion on air pollution and climate change.

A long-term decline in downward surface solar radiation.

Downward surface solar radiation (DSSR) is critical for the Earth system. It is well-known that DSSR over land has fluctuated on decadal timescales in the past. By utilizing a combination of station observations and the latest CMIP6 simulations, here we show that DSSR had a global consistent decline during 1959-2014, with comparable contributions from greenhouse gases (GHGs) 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 increasing 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 surface 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 thus leading to a brighter future.

Changes in the Climate Effects of Major Anthropogenic Aerosols in East Asia Under Different Emission Reduction Scenarios in China

AbstractPollutant emissions in China have significantly decreased over the past decade and are expected to continue declining in the future. Aerosols, as important pollutants and short‐lived climate forcing agents, have significant but currently unclear climate impacts in East Asia as their concentrations decrease until mid‐century. Here, we employ a well‐developed regional climate model RegCM4 combined with future pollutant emission inventories, which are more representative of China to investigate changes in the concentrations and climate effects of major anthropogenic aerosols in East Asia under six different emission reduction scenarios (1.5°C goals, Neutral‐goals, 2°C ‐goals, NDC‐goals, Current‐goals, and Baseline). By the 2060s, aerosol surface concentrations under these scenarios are projected to decrease by 89%, 87%, 84%, 73%, 65%, and 21%, respectively, compared with those in 2010–2020. Aerosol climate effect changes are associated with its loadings but not in a linear manner. The average effective radiative forcing at the surface in East Asia induced by aerosol‐radiation‐cloud interactions will diminish by 24% ± 13% by the 2030s and 35% ± 13% by the 2060s. These alternations caused by aerosol reductions lead to increases in near‐surface temperatures and precipitations. Specifically, aerosol‐induced temperature and precipitation responses in East Asia are estimated to change by −78% to −20% and −69% to 77%, respectively, under goals with different emission scenarios in the 2060s compared to 2010–2020. Therefore, the significant climate effects resulting from substantial reductions in anthropogenic aerosols need to be fully considered in the pathway toward carbon neutrality.

Radiative forcing from the 2020 shipping fuel regulation is large but hard to detect

Reduction in aerosol cooling unmasks greenhouse gas warming, exacerbating the rate of future warming. The strict sulfur regulation on shipping fuel implemented in 2020 (IMO2020) presents an opportunity to assess the potential impacts of such emission regulations and the detectability of deliberate aerosol perturbations for climate intervention. Here we employ machine learning to capture cloud natural variability and estimate a radiative forcing of +0.074 ±0.005 W m−2 related to IMO2020 associated with changes in shortwave cloud radiative effect over three low-cloud regions where shipping routes prevail. We find low detectability of the cloud radiative effect of this event, attributed to strong natural variability in cloud albedo and cloud cover. Regionally, detectability is higher for the southeastern Atlantic stratocumulus deck. These results raise concerns that future reductions in aerosol emissions will accelerate warming and that proposed deliberate aerosol perturbations such as marine cloud brightening will need to be substantial in order to overcome the low detectability.

Warming effects of reduced sulfur emissions from shipping

Abstract. The regulation introduced in 2020 that limits the sulfur content in shipping fuel has reduced sulfur emissions over global open oceans by about 80 %. This is expected to have reduced aerosols that both reflect solar radiation directly and affect cloud properties, with the latter also changing the solar radiation balance. Here we investigate the impacts of this regulation on aerosols and climate in the HadGEM3-GC3.1-LL climate model. The global aerosol effective radiative forcing caused by reduced shipping emissions is estimated to be 0.13 W m−2, which is equivalent to an additional ∼50 % to the net positive forcing resulting from the reduction in all anthropogenic aerosols from the late-20th century to the pre-2020 era. Ensembles of global coupled simulations from 2020–2049 predict a global mean warming of 0.04 K averaged over this period. Our simulations are not clear on whether the global impact is yet to emerge or has already emerged because the present-day impact is masked by variability. Nevertheless, the impact of shipping emission reductions either will have already committed us to warming above the 1.5 K Paris target or will represent an important contribution that may help explain part of the rapid jump in global temperatures over the last 12 months. Consistent with previous aerosol perturbation simulations, the warming is greatest in the Arctic, reaching a mean of 0.15 K Arctic-wide and 0.3 K in the Atlantic sector of the Arctic (which represents a greater than 10 % increase in the total anthropogenic warming since pre-industrial times).

Influence of changes in anthropogenic and natural sources on global aerosol optical depth during COVID-19 lockdown: Ground-based observations, satellites, models

Influence of changes in anthropogenic and natural sources on global aerosol optical depth during COVID-19 lockdown: Ground-based observations, satellites, models

Reduction of aerosol and droplet dispersions using intraoral and extraoral vacuums for dental treatments with face-up, diagonal and upright positions

PurposeThe COVID-19 pandemic has affected lives and dental treatment. Aerosols and droplets generated during dental treatment present a risk of infection for dental care workers. However, detailed elucidation of the conditions under which those are generated has yet to be presented, and no clear countermeasures for protection have been established. The present study aimed to clarify the process of generation of aerosol and droplets in dental treatment, as well as their dynamics for establishment of effective countermeasures and protection strategies.MethodsImages were obtained using a high-speed camera of aerosol and droplets generated during dental treatments performed on a mannequin. The effects of intraoral vacuum and extraoral vacuum to reduce those, as well as splash range with different body position were examined. Quantitative evaluations of aerosol and droplets were also performed using water-sensitive paper.ResultsAerosol and droplets quantities were significantly reduced by use of both intraoral and extraoral vacuums as compared to no vacuum in both image analysis and findings obtained with water-sensitive paper (p < 0.05). Additionally, the intensity of aerosol and droplets when using the intraoral and extraoral vacuum devices with a body position of 45 degrees was a significantly less as compared to the other settings (p < 0.001).ConclusionsThe present study demonstrated the effectiveness of visualization of the aerosol and droplets generated by dental tools using a high-speed camera. Use of an extraoral vacuum resulted in a reduction of those generated during simulated dental treatment, and also contributed to diffusion prevention to protect the operator and assistant. Nevertheless, it is necessary to be careful because the use of extraoral vacuums may reverse the spread of aerosol and droplets depending on the position of patient.

Reduction of Submicron-Sized Aerosols by Aerodynamically Assisted Electrical Attraction with Micron-Sized Aerosols

A vortex generator was installed inside an electric agglomeration device to apply aerodynamic agglomeration in the same space as electric agglomeration. Computational fluid dynamics simulation was utilized to assess the combined effects of electric and aerodynamic agglomeration, and this was subsequently validated through experiments. The discrete phase model was used to track particle trajectories. The results showed that both the aerodynamic agglomeration through the vortex generator and the electric agglomeration through the electric field were effective. When these two agglomerations existed individually in series, the total removal efficiency for submicron particles was 32.5%. However, when they coexisted in the same space, the efficiency increased to 50%. This increase is attributed to the increase in residence time when the vortex generator was added to a space with an electric field. This led to particles being exposed to the electric field for a longer duration, thus generating a synergistic effect.

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

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

Can satellite products monitor solar brightening in Europe?

Satellite products provide the best way to monitor the solar radiation reaching the Earth’s surface on a global scale. However, their capability to monitor solar radiation trends needs to be constantly evaluated. This depends on their temporal stability and the accurate representation of all processes driving solar radiation. This study evaluates these aspects by comparing and cross-comparing different solar radiation products (ERA5, CAMS-RAD 4.6, SARAH-3, CLARA-A3, CERES-EBAF 4.2) against in-situ measurements over Europe.All products show a moderate positive bias over Europe but strong differences in their root mean squared deviation (RMSD) related to their different cloud transmittance models. Geostationary-based products (SARAH-3, CAMS-RAD 4.6) provide the smallest RMSD closely followed by CLARA-A3, whereas ERA5 shows a large RMSD due to random errors in cloud transmittance.All products show an increase in surface solar radiation, or brightening, over the last 40 years over Europe, but the magnitude of the trends and their spatiotemporal variability differ between products. Despite finding temporal inhomogeneities in some products, the different trends are mostly due to different aerosol modeling approaches implemented by each product. Both SARAH-3 (+2.3 W/m2/decade, 2001–22) and CERES-EBAF 4.2 (+2.2 W/m2/decade, 2001–22) provide the most consistent trends compared to in-situ data, showing that after stabilizing in the late 2000s, brightening is particularly recovering in Western Europe. In-situ measurements show a reduction of aerosol optical depth from 2001 to 2022 that has been accentuated in the last 10 years, particularly in Western Europe. This would be consistent with the hypothesis that brightening recovery is driven by an aerosol reduction, though other analyses suggest that clouds also play a role in this recovery. More work is needed to understand the contribution of aerosols to solar radiation trends and the exact aerosol effects represented by each solar radiation product.

Microphysical Analysis of Maritime and Continental Aerosols: Determination of Hygroscopic Growth Factors Using OPAC Data and Modeling Approaches

Study’s Excerpt/Novelty This study presents an application of mass-based hygroscopicity models to analyze microphysical properties of atmospheric aerosols from continental and maritime sources using data from the Optical Properties of Aerosols and Clouds (OPAC). By examining hygroscopic growth factors and effective radii at eight different relative humidities, the research highlights the significant variation in growth factors between maritime and continental aerosols, with maritime clean aerosols exhibiting a substantially higher growth factor at 99% RH. The study's robust statistical analysis, confirmed by R² values greater than 90% and significance levels below 0.05, demonstrates the model's efficacy for atmospheric modeling and remote sensing applications. Full Abstract The interplay of marine and continental sources governed the atmospheric aerosols over coastal areas. The transport of aerosols from continental sources into sea surfaces through deposition or diffusion is what causes the fast reduction of continental aerosols. A mass based based hygroscopicity models were applied to the data extracted from the Optical Properties of Aerosols and Clouds (OPAC). The microphysical properties obtained were radii, density, refractive index, mass, volume, and sphericity of the atmospheric aerosols of continental and maritime aerosols at eight different relative humidity of 0%, 50%, 70%, 80%, 90%, 95%, 98%, and 99%. Using the microphysical properties, hygroscopic growth factors, and effective radii of the mixtures, mass growth factor Gm and diameter growth factor DG were determined, and also the parameter Km for mass based of the aerosols were determined using multiple regression analysis with SPSS 16.0 at each relative humidity. The results show that Gm for maritime clean is higher than other aerosols, with a value of 34.46 at 99% RH, while the lowest value is for continental average, with a value of 5.03 at 99% RH. Also, R2 for the model is greater than 90%. The significance and P-values are less than 0.05; therefore, the model is good for atmospheric modeling and remote sensing.

Terrestrial Carbon Sink and Clean Air Co‐Benefits From China's Carbon Neutrality Policy

AbstractAs the world's largest carbon emitter, China has been confronting the dual challenge of climate change and air pollution. China's quest for reducing carbon emissions will promisingly benefit the air quality, yet its impact on carbon sinks remains unclear. Here, we assess the effect of China's clean air actions and carbon neutrality policy on air quality and its associated co‐benefits for terrestrial carbon sinks by integrating multiple observations and numerical modeling. We find a quadratic response of plant photosynthesis to aerosol loading due to trade‐offs between diffuse fertilization effect and light limitations. The estimations show that China's air pollution suppresses terrestrial carbon uptake through aerosol‐induced light limitations, leading to a 7.3% decrease in plant productivity in the 2010s. In the context of carbon neutrality pledge, the associated aerosol reductions tend to alleviate the suppression and produce an additional CO2 removal of 0.39 GtCO2 year−1. Our results uncover the enhanced terrestrial carbon sinks by aerosol mitigation, highlighting the synergy between carbon neutrality and clean air.

Increased projected changes in quasi-resonant amplification and persistent summer weather extremes in the latest multimodel climate projections

High-amplitude quasi-stationary atmospheric Rossby waves with zonal wave numbers 6–8 associated with the phenomenon of quasi-resonant amplification (QRA) have been linked to persistent summer extreme weather events in the Northern Hemisphere. QRA is not well-resolved in current generation climate models, therefore, necessitating an alternative approach to assessing their behavior. Using a previously-developed fingerprint-based semi-empirical approach, we project future occurrence of QRA events based on a QRA index derived from the zonally averaged surface temperature field, comparing results from CMIP 5 and 6 (Coupled Model Intercomparison Project). There is a general agreement among models, with most simulations projecting substantial increase in QRA index. Larger increases are found among CMIP6-SSP5-8.5 (42 models, 46 realizations), with 85% of models displaying a positive trend, as compared with 60% of CMIP5-RCP8.5 (33 models, 75 realizations), with a reduced spread among CMIP6-SSP5-8.5 models. CMIP6-SSP3-7.0 (23 models, 26 realizations) simulations display qualitatively similar behavior to CMIP6-SSP5-8.5, indicating a substantial increase in QRA events under business-as-usual emissions scenarios, and the results hold regardless of the increase in climate sensitivity in CMIP6. Projected aerosol reductions in CMIP6-SSP3-7.0-lowNTCF (5 models, 16 realizations) lead to halting effect in QRA index and Arctic Amplification during the 1st half of the twenty-first century. Our analysis suggests that anthropogenic warming will likely lead to an even more substantial increase in QRA events (and associated summer weather extremes) than indicated by past analyses.