Aerosol Reduction Research Articles

Computational fluid dynamics simulation of SARS-CoV-2 aerosol dispersion inside a grocery store

Grocery stores provide essential services to communities all over the world. The COVID-19 pandemic has necessitated better understanding of the transport and dynamics of aerosolized viruses, particularly for the assessment of infection transmission risk within grocery stores and for other providers of essential services. In this study, a 3D computational fluid dynamics model was developed for a medium-sized grocery store in the United States using Ansys Fluent software. Different cases were simulated of a single infected person releasing viral aerosols with and without wearing a face mask. Results showed characteristic airflow and temperature distribution patterns inside the store that can drive the indoor dispersal of viral aerosols. Unsteady spatial distribution of mean age of air was used as a metric to indirectly quantify areas of higher risk of infection. Several factors affected the localization of suspended viral aerosols. Major recirculation patterns in certain locations of the store caused by persistent eddies were primarily attributed to increased mean age of air. The maximum mean age of air in the grocery store was found to be less than 30 min. Simulation results indicate that, without wearing a face mask, the aerosol particles released from a coughing infected person can be spread throughout nearly one-quarter of the grocery store in less than 6 min. The source-control strategy with a face mask showed significant reduction of viral aerosols being dispersed indoors.

Does Regional Hydroclimate Change Scale Linearly With Global Warming?

AbstractMany aspects of climate change scale linearly with global warming. However, nonlinear changes are possible, especially in the context of hydroclimate, and under emissions scenarios with stabilized global temperature, as aspired to by current climate targets. In CMIP5 and 6, a progressively larger land area shows nonlinear changes as a function of global warming when considering precipitation, evaporation, and soil moisture, with the latter showing nonlinearity over ∼50% of global land. Using ensemble simulations with the Community Earth System Model 1, in which individual forcing factors are held constant, we illustrate how nonadditive responses to anthropogenic greenhouse gases and industrial and fire‐related aerosols can yield complex soil moisture changes in certain regions. This complexity contributes to uncertainty in regional soil moisture projections and suggests that the timing of, as well as model response uncertainty to, future aerosol reductions will have significant impacts on regional hydroclimate change as global temperatures stabilize.

Reduction of aerosols and splatter generated during ultrasonic scaling by adding food-grade thickeners to coolants: an in-vitro study.

ObjectiveThe effectiveness of using food-grade coolant thickener solutions on the amount of aerosols generated and splatter contamination spread distance during simulated ultrasonic scaling was examined.Materials and methodsThe study was performed using a phantom lower jaw placed on a black box. Simulated ultrasonic scaling was performed for 2 min using four coolant solutions: distilled water (control), 2% wt. polyacrylic acid (PAA), 0.4% wt. xanthan gum (XA), and 0.4% wt. carboxymethyl cellulose (CMC). The simulation was repeated 10 times for each coolant group. The generated aerosols and droplets were quantified using a handheld particle counter, and the splatter contamination spread distance was evaluated by adding tracing fluorescent dye to the coolant reservoir supplying the scaler unit. One-way multivariate analysis of variance was performed to determine the difference among coolant groups (a = .05).ResultsThe amount of aerosols and droplets and splatter contamination distance (p < .001) pertaining to the three food-grade coolant thickener solutions were considerably lower than those for the distilled water (control). The PAA group exhibited a significantly lower splatter contamination distance (p < .001) and a number of generated droplets (p = .031) than those of the XA group. The CMC group exhibited a significantly lower splatter contamination distance (p < .001) than that of the XA group. No statistically significant difference was observed between the PAA and CMC in terms of the three dependent variables (p > .05).ConclusionThe food-grade coolant thickeners could reduce the amount of generated aerosols and splatter contamination distance but not completely eliminate them. PAA and CMC solutions were more effective in reducing the aerosol/splatter during scaling compared to XA.Clinical relevanceMany dental procedures generate aerosols and splatter, which pose a potential risk to the patients and dental personnel, especially during the current COVID-19 pandemic.

Competing effects of aerosol reductions and circulation changes for future improvements in Beijing haze

Abstract. Despite local emission reductions, severe haze events remain a serious issue in Beijing. Previous studies have suggested that both greenhouse gas increases and aerosol decreases are likely to increase the frequency of weather patterns conducive to haze events. However, the combined effect of atmospheric circulation changes and aerosol and precursor emission changes on Beijing haze remains unclear. We use the Shared Socioeconomic Pathways (SSPs) to explore the effects of aerosol and greenhouse gas emission changes on both haze weather and Beijing haze itself. We confirm that the occurrence of haze weather patterns is likely to increase in future under all SSPs and show that even though aerosol reductions play a small role, greenhouse gas increases are the main driver, especially during the second half of the 21st century. However, the severity of the haze events decreases on decadal timescales by as much as 70 % by 2100. The main influence on the haze itself is the reductions in local aerosol emissions, which outweigh the effects of changes in atmospheric circulation patterns. This demonstrates that aerosol reductions are beneficial, despite their influence on the circulation.

Sensitivity analysis of SARS-CoV-2 aerosol exposure.

As vaccination campaigns are in progress in most countries, hopes to win back more normality are rising. However, the exact path from a pandemic to an endemic virus remains uncertain. While in the pre-vaccination phase many critical indoor situations were avoided by strict control measures, for the transition phase a certain mitigation of the effect of indoor situations seems advisable. To better understand the mechanisms of indoor airborne transmissions, we present a new time-discrete model to calculate the level of exposure towards infectious SARS-CoV-2 aerosol and carry out a sensitivity analysis for the level of SARS-CoV-2 aerosol exposure in indoor settings. Time limitations and the use of any kind of masks were found to be strong mitigation measures, while how far the effort for a strict use of professional face pieces instead of simple masks can be justified by the additional reduction of the exposure dose remains unclear. Very good ventilation of indoor spaces is mandatory. The definition of sufficient ventilation in regard to airborne SARS-CoV-2 transmission follows other rules than the standards in ventilation design. This means that especially smaller rooms most likely require a significantly greater fresh air supply than usual. Further research on 50% group models in schools is suggested. The benefits of a model in which the students come to school every day, but for a limited time, should be investigated. In terms of window ventilation, it has been found that many short opening periods are not only thermally beneficial, they also reduce the exposure dose. The fresh air supply is driven by the temperature gradient and wind speed. However, the sensitivity towards these parameters is not very high and in times of low wind and temperature gradients, there are no arguments against keep windows open in order to make up for the reduced air flow rate. Long total opening periods and large window surfaces will strongly reduce the exposure. Additionally, the results underline the expectable fact that exposure doses will increase when hygiene and control measures are reduced. It seems advisable to investigate what this means for the infection rate and the fatality of infections in populations with partial immunity. Very basic considerations suggest that the value of aerosol reduction measures may be reduced with very infectious variants such as delta.

Reduction in European anthropogenic aerosols and the weather conditions conducive to PM2.5 pollution in North China: a potential global teleconnection pathway

Frequent and severe PM2.5 pollution over China seriously harms natural environment and human health. Changes in meteorological conditions in recent decades have been recognized to contribute to the long-term increase in PM2.5 pollution in North China (NC). However, the dominant climatic factors driving the interdecadal changes of the weather conditions conducive to PM2.5 pollution remain unclear. Here we identify a potential global teleconnection mechanism: the decadal reduction in European aerosol emissions since the 1980s may have partially contributed to the interdecadal increase in weather conditions conducive to PM2.5 pollution in NC, measured by an Emission-weighted Air Stagnation Index (ASIE) that increases at a rate of 6.2% decade−1 (relative to the 1981–1985 level). By regression analysis, we show that the decreased European aerosol loadings can warm the lower atmosphere and induce anomalous ascending motion in Europe, which potentially stimulates two anomalous Rossby wave trains in the upper troposphere travelling eastward across Eurasia. The teleconnection patterns project on NC by weakening the near-surface horizontal dispersion, which may be favorable to the increase in local ASIE and air pollution build-up. The suggested mechanism is further supported by the results from a set of large-ensemble simulations, showing that the European aerosol emission decline since the 1980s excites similar local heating and ascending motion and leads to increasing trends of 0.1–0.5 μg m−3 (38 year)−1 in surface sulfate concentrations over most of NC. This proposed ‘West-to-East Aerosol-to-Aerosol’ teleconnection mechanism helps resolve opposite views on the impact of global versus local aerosol forcing on PM2.5 pollution weather in NC. The policy implication is that the sustained decline in European aerosol emissions in coming decades, in conjunction with unabated global and regional warming, could further exacerbate air pollution in NC, thus imposing stronger pressure to reduce local emission sources quicker and deeper.

A comprehensive research on the global all-sky surface solar radiation and its driving factors during 1980–2019

The study evaluated monthly surface solar radiation (SSR) by the second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) reanalysis and investigated the long-term trend of SSR in regions with excellent performance of reanalysis worldwide. Overall, MERRA-2 performed well in North America (NA), Europe (EUR), Northern East Asia (NEA) and Oceania (OCE). The results suggest that from 1980 to 2019, there has been a widespread downtrend of SSR in NA, NEA and OCE, at −0.316, −0.001 and − 1.140 W m−2 decade−1, respectively, an uptrend at 0.633 W m−2 decade−1 of EUR. NA showed the strongest brightness by 5.886 W m−2 decade−1 in 1982–1991. This was associated with the decrease of low cloud fraction (−0.024 decade−1), resulting in the weakening (3.164 W m−2 decade−1) of the attenuation effect of cloud on radiation. In EUR, SSR was also affected by cloud changes. The attenuation effect of clouds on SSR was weakened in 1981–1990 and enhanced in 1989–1998, which led to the strongest brightening (4.556 W m−2 decade−1) and dimming (−1.587 W m−2 decade−1), respectively. And in NEA, the reduction of clouds and aerosols dominated the strong brightening by 4.721 W m−2 decade−1 during 1992–2001. In addition, NEA experienced the strongest dimming during 1997–2006, which was mainly related to the increase of aerosols. Finally, in OCE, SSR was primarily affected by the water vapor and cloud together, and the strongest brightening (10.130 W m−2 decade−1) and the strongest dimming (−8.892 W m−2 decade−1) occurred in 2010–2019 and 2001–2011, respectively.

Self Prepared Herbal Mouthwash Used As Pre-procedural Rinse in Reducing Dental Aerosol: A Substitute to Chemical Mouthrinse: A Clinico-Microbiological Study

Aim:To evaluate and compare the efficacy of pre-procedural mouth rinses in reducing microbial content of aerosol product during ultrasonic-scaling procedures by viable bacterial count.Materials And Methods:5 patients were assigned in each group: A- Neem, B -CHX, C-Triphala, D - Control Group.In Group A, B, C -Patient were asked to rinse their mouth with 10 ml mouthwash for 30 seconds before SRP, of which A and C are self- prepared herbal mouthwashes i.e Triphala and Neem. Aerosol will be collected, cultured and incubated on blood agar plates at specified sites from operator. CFU will be counted and result will be assessed statistically. Conclusion: The study suggests that 10 ml of Neem Mouth rinse when used 10 minutes prior to ultrasonic scaling is more potent in reducing the aerosol contamination as compared to the Triphala mouth rinse and commercially available 0.2 % Chlorhexidine mouthrinse. Also the reduction in aerosol content was seen in Tray location when rinsed with CHX and aerosol reduction in Spitoon and Chest location while rinsing with Neem mouthrinse.

In Vivo Study of Aerosol, Droplets and Splatter Reduction in Dentistry.

Oral health care workers (OHCW) are exposed to pathogenic microorganisms during dental aerosol-generating procedures. Technologies aimed at the reduction of aerosol, droplets and splatter are essential. This in vivo study assessed aerosol, droplet and splatter contamination in a simulated clinical scenario. The coolant of the high-speed air turbine was colored with red concentrate. The red aerosol, droplets and splatter contamination on the wrists of the OHCW and chests of the OHCW/volunteer protective gowns, were assessed and quantified in cm2. The efficacy of various evacuation strategies was assessed: low-volume saliva ejector (LV) alone, high-volume evacuator (HV) plus LV and an extra-oral dental aerosol suction device (DASD) plus LV. The Kruskal–Wallis rank-sum test for multiple independent samples with a post-hoc test was used. No significant difference between the LV alone compared to the HV plus LV was demonstrated (p = 0.372059). The DASD combined with LV resulted in a 62% reduction of contamination of the OHCW. The HV plus LV reduced contamination by 53% compared to LV alone (p = 0.019945). The DASD demonstrated a 50% reduction in the contamination of the OHCWs wrists and a 30% reduction in chest contamination compared to HV plus LV. The DASD in conjunction with LV was more effective in reducing aerosol, droplets and splatter than HV plus LV.

English

BACKGROUND The objective of the study was to determine the efficacy of Triphala as a preprocedural mouth rinse &amp; comparing the efficacy with chlorhexidine and betadine in reducing the viable microbial load in dental aerosols. METHODS 32 patients with chronic periodontitis were randomly allocated into 4 groups (A, B, C &amp; D) of 8 patients each who received 0.2 % chlorhexidine (CHX), 6 % Triphala (TRP), 2 % betadine and water respectively as a pre-procedural mouth rinse. Blood agar plates were placed on the operator’s chest area and the patient’s chest area for collecting the aerosols. The agar plates were then incubated at 370C for 48 hours and colony-forming units (CFUs) were counted. RESULTS CFU was significantly reduced in groups A, B &amp; C compared to group D. Intergroup comparison showed no significant difference in the efficacy of 0.2 % CHX and 6 % TRP with P-value 0.058 in the operator’s area and with a significant difference of Pvalue 0.014 in the patient’s area. 2 % betadine was found to be least effective among the 3 test groups. The number of CFUs was greater at the patient’s chest area than that of the operator. CONCLUSIONS This study reinforces the importance of preprocedural mouth rinse. Triphala showed near equal efficacy to CHX, which is considered the gold standard in aerosol reduction and also better than 2 % betadine. Therefore, it can be considered as an alternative to CHX as a preprocedural mouth rinse. KEY WORDS Triphala, Chlorhexidine, Betadine, Aerosols, Colony Forming Units (CFUs)

Characterization and mitigation of aerosols and spatters from ultrasonic scalers

BackgroundDental procedures often produce aerosols and spatter, which have the potential to transmit pathogens such as severe acute respiratory syndrome coronavirus 2. The existing literature is limited. MethodsAerosols and spatter were generated from an ultrasonic scaling procedure on a dental manikin and characterized via 2 optical imaging methods: digital inline holography and laser sheet imaging. Capture efficiencies of various aerosol mitigation devices were evaluated and compared. ResultsThe ultrasonic scaling procedure generated a wide size range of aerosols (up to a few hundred μm) and occasional large spatter, which emit at low velocity (mostly < 3 m/s). Use of a saliva ejector and high-volume evacuator (HVE) resulted in overall reductions of 63% and 88%, respectively, whereas an extraoral local extractor (ELE) resulted in a reduction of 96% at the nominal design flow setting. ConclusionsThe study results showed that the use of ELE or HVE significantly reduced aerosol and spatter emission. The use of HVE generally requires an additional person to assist a dental hygienist, whereas an ELE can be operated hands free when a dental hygienist is performing ultrasonic scaling and other operations. Practical ImplicationsAn ELE aids in the reduction of aerosols and spatters during ultrasonic scaling procedures, potentially reducing transmission of oral or respiratory pathogens like severe acute respiratory syndrome coronavirus 2. Position and airflow of the device are important to effective aerosol mitigation.

Assessment of the emission mitigation effect on the wintertime air quality in the Guanzhong Basin, China from 2013 to 2017

With the completion of the Air Pollution Prevention and Control Action Plan (Action Plan) in the Guanzhong Basin (GZB), the wintertime fine particulate matters (PM2.5) concentration has decreased by 50.0 μg m−3 (33.4%) from 2013 to 2017. Considering the significant impacts of meteorological conditions on particulate pollution, the effectiveness of anthropogenic emissions abatement on the PM2.5 reduction in the GZB remain unclear. In this study, the WRF-Chem model was used to quantitatively evaluate the effectiveness of emissions mitigation on the particulate pollution in the GZB in December from 2013 to 2017. The model typically showed an affordable consistence with observations and simulation in meteorological parameters, atmospheric pollutants, and aerosol components. Sensitivity results revealed that emissions reduction decreases PM2.5 concentrations by around 17% in the GZB, about half of the observed PM2.5 decreased in December from 2013 to 2017, showing significant role of meteorological conditions in modulating particulate pollution. Emissions mitigation also decreased SO2, CO and O3 concentrations by around 55%, 17%, and 7%, respectively, but increased NO2 concentrations by 27%. Additionally, the PM2.5 decrease in the GZB is mainly contributed by the reduction of sulfate and primary organic aerosols, caused by implementation of stringent SO2 mitigation measures and reduced coal use. However, the mitigation of elemental carbon, dust and nitrate aerosols are not significant, particularly with regarding to nitrate aerosols, which is influenced by increase of NO2 and decrease of sulfate. Specified emissions mitigation strategies need to be designed to further lower the PM2.5 level in the GZB.

Dental Laser in The Covid-19 Era

Despite the many historical events during the year 2020, this period of time will forever be remembered as the year of COVID-19. Since its onset in November 2019, The Sars-CoV-2 has made an enormous impact across all aspects of society across the entire world. Globally as of July 5th, 2021, there have been 184000000 confirmed cases of COVID-19, which tragically include 3980000 deaths.&#x0D; Sars-CoV-2 is spread through the respiratory system with the primary modes of transmission being aerosol, respiratory droplets, and direct contact.&#x0D; It is of great importance to understand that one of the primary modes of transmission, the aerosol (bioaerosol) mode is a mode that is omnipresent in most dental settings.&#x0D; To prevent dissemination of disease in American dental offices, the CDC and the ADA have developed strict protocols for dental care providers to follow.&#x0D; Protocols include case selection, protective equipment (PPE), Covid testing, procedure risk stratification, and reduction of aerosols. Laser-assisted dentistry has been identified as a potential key modality in the reduction of bio aerosols.

Aerosol Direct Radiative Effects under Cloud-Free Conditions over Highly-Polluted Areas in Europe and Mediterranean: A Ten-Years Analysis (2007–2016)

This study investigates changes in aerosol radiative effects on two highly urbanized regions across the Euro-Mediterranean basin with respect to a natural desert region as Sahara over a decade through space-based lidar observations. The research is based on the monthly-averaged vertically-resolved aerosol optical depth (AOD) atmospheric profiles along a 1∘×1∘ horizontal grid, obtained from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument measurements aboard the Cloud-Aerosol lidar and Infrared Pathfinder Satellite Observation (CALIPSO). To assess the variability of the anthropogenic aerosols on climate, we compared the aerosol vertical profile observations to a one-dimensional radiative transfer model in two metropolitan climate sensible hot-spots in Europe, namely the Po Valley and Benelux, to investigate the variability of the aerosol radiative effects over ten years. The same analysis is carried out as reference on the Sahara desert region, considered subject just to natural local emission. Our findings show the efficacy of emission reduction policies implemented at government level in strongly urbanized regions. The total atmospheric column aerosol load reduction (not observed in Sahara desert region) in Po Valley and Benelux can be associated with: (i) an increase of the energy flux at the surface via direct effects confirmed also by long term surface temperature observations, (ii) a general decrease of the atmospheric column, and likely (iii) an increase in surface temperatures during a ten-year period. Summarizing, the analysis, based on the decade 2007–2016, clearly show an increase of solar irradiation under cloud-free conditions at the surface of +3.6 % and +16.6% for the Po Valley and Benelux, respectively, and a reduction of −9.0% for the Sahara Desert.

The impact of improved air-quality due to COVID-19 lockdown on surface meteorological parameters and planetary boundary layer over Gadanki, a tropical rural site in India

The nation-wide lockdowns imposed in India during March‐–May 2020 (in four phases) to curb the spread of the novel Corona virus, greatly enhanced the near-surface air-quality due to lowering of industrial, transport and human activities. The present study focuses on the changes in the vertical structure of aerosol concentration and how those changes impacted radiation balance, the planetary boundary layer (PBL) height and surface meteorological parameters. Instrumented tower and Ceilometer measurements made at Gadanki (13.45°N, 79.18°E), located in a rural environment, coupled with satellite-derived Aerosol Optical Depth (AOD) data have been used to understand the changes in lockdown period. Significant reduction in backscatter density during the lockdown compared to 2019 indicates that aerosol reduction during the lockdown is not only limited to the surface, rather observed in the entire PBL. Except for the fourth phase of lockdown during which several relaxations have been given for vehicular movement and other anthropogenic activities, the reduction in backscatter density is seen in all phases of lockdown. However, the reduction is prominently seen in the second and third phases. The AOD also reduced by 40% around Gadanki, comparable to that of in urban regions. Due to the reduction in aerosols during the lockdown period, the insolation increases by 60 Wm−2, which is expected to increase the temperature. However, the increased loss of long-wave radiation (due to reduction in trapping gases) and more rain events during the lockdown period decreased the temperature by ~1 °C. Measurements also suggest that the most of net radiation is partitioned into the latent heat flux increasing the humidity and lowering the PBL height (due to reduced strength of thermals and sensible heat flux).

Enhancement of peripheral seal of medical face masks using a 3-dimensional–printed custom frame

BackgroundDuring the COVID-19 pandemic, American Society for Testing and Materials level 3 and level 2 medical face masks (MFMs) have been used for most health care workers and even for the first responders owing to a shortage of N95 respirators. However, the MFMs lack effective peripheral seal, leading to concerns about their adequacy to block aerosol exposure for proper protection. The purpose of this study was to evaluate the peripheral seal of level 3 and level 2 MFMs with a 3-dimensional (3D-) printed custom frame. MethodsLevel 3 and level 2 MFMs were tested on 10 participants with and without a 3D-printed custom frame; the efficiency of mask peripheral seal was determined by means of quantitative fit testing using a PortaCount Fit Tester based on ambient aerosol condensation nuclei counter protocol. ResultsThe 3D-printed custom frame significantly improved the peripheral seal of both level 3 and level 2 MFMs compared with the masks alone (P < .001). In addition, both level 3 and level 2 MFMs with the 3D-printed custom frame met the quantitative fit testing standard specified for N95 respirators. Practical ImplicationsThe 3D-printed custom frame over level 3 and level 2 MFMs can offer enhanced peripheral reduction of aerosols when using collapsible masks. With the shortage of N95 respirators, using the 3D-printed custom frame over a level 3 or level 2 MFM is considered a practical alternative to dental professionals.

Novel measurement system for respiratory aerosols and droplets in indoor environments.

The SARS‐CoV‐2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol‐emitting mannequin (emitter) and a number of portable aerosol‐absorbing mannequins (recipients) was developed that can measure the spread of aerosols and droplets that potentially contain infectious viruses. The emission of the virus from a human is simulated by using tracer particles solved in water. The recipients inhale the aerosols and droplets and quantify the level of solved tracer particles in their artificial lungs simultaneously over time. The mobile system can be arranged in a large variety of spreading scenarios in indoor environments and allows for quantification of the infection probability due to airborne virus spreading. This study shows the accuracy of the new measurement system and its ability to compare aerosol reduction measures such as regular ventilation or the use of a room air purifier.

Economic Shock in a Climate Scenario and Its Impact on Surface Temperatures

AbstractA socio‐economic crisis was added to the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathway 8.5 (RCP8.5) scenario. This idealized climate scenario was simulated using the Community Earth System Model version 1.2.2 to determine the transient climate response to a two‐year reduction of anthropogenic emissions. Global and regional (Asian, North American and European) mean surface temperatures (MSTs) were significantly warmer than baseline for 5 years. This was followed by cooler‐than‐baseline MSTs lasting for about two decades until the end of the simulation. Emission reduction of only carbon dioxide (CO2) resulted in multi‐decadal cooler‐than‐baseline MSTs. Emission reduction of aerosols and aerosol precursors resulted in strong short‐term warmer‐than‐baseline MSTs for the first five years after the start of the crisis. This was followed by weaker multi‐decadal warmer‐than‐baseline MSTs. The greatest warming occurred over Europe. This could be explained by the inter‐scenario differences in the state of the North Atlantic Oscillation. However, global, Asian and North American MSTs were all warmer than baseline.

Large Differences in Diffuse Solar Radiation Among Current-Generation Reanalysis and Satellite-Derived Products

AbstractThough the partitioning of shortwave radiation (K↓) at the surface into its diffuse (K↓,d) and direct beam (K↓,b) components is relevant for, among other things, the terrestrial energy and carbon budgets, there is a dearth of large-scale comparisons of this partitioning across reanalysis and satellite-derived products. Here we evaluate K↓, K↓,d, and K↓,b, as well as the diffuse fraction (kd) of solar radiation in four current-generation reanalysis (NOAA-CIRES-DOE, NCEP/NCAR, MERRA-2, ERA5) datasets and one satellite-derived product (CERES) using ≈1400 site years of observations. Although the systematic positive biases in K↓ is consistent with previous studies, the biases in gridded K↓,d and K↓,b vary in direction and magnitude, both annually and across seasons. The inter-model variability in cloud cover strongly explains the biases in both K↓,d and K↓,b. Over Europe and China, the long-term (10-year plus) trends in K↓,d in the gridded products are noticeably differ from corresponding observations and the grid-averaged 35-year trends show an order of magnitude variability. In the MERRA-2 reanalysis, which includes both clouds and assimilated aerosols, the reduction in both clouds and aerosols reinforce each other to establish brightening trends over Europe, while the effect of increasing aerosols overwhelm the effect of decreasing cloud cover over China. The inter-model variability in kd seen here (0.27 to 0.50 from CERES to MERRA-2) suggests substantial differences in shortwave parameterization schemes and their inputs in climate models and can contribute to inter-model variability in coupled simulations. Based on these results, we call for systematic evaluations of K↓,d and K↓,b in CMIP6 models.

Future changes in Beijing haze events under different anthropogenic aerosol emission scenarios

Abstract. Air pollution is a major issue in China and one of the largest threats to public health. We investigated future changes in atmospheric circulation patterns associated with haze events in the Beijing region and the severity of haze events during these circulation conditions from 2015 to 2049 under two different aerosol scenarios: a maximum technically feasible aerosol reduction (MTFR) and a current legislation aerosol scenario (CLE). In both cases greenhouse gas emissions follow the Representative Concentration Pathway 4.5 (RCP4.5). Under RCP4.5 with CLE aerosol the frequency of circulation patterns associated with haze events increases due to a weakening of the East Asian winter monsoon via increased sea level pressure over the North Pacific. The rapid reduction in anthropogenic aerosol and precursor emissions in MTFR further increases the frequency of circulation patterns associated with haze events, due to further increases in the sea level pressure over the North Pacific and a reduction in the intensity of the Siberian high. Even with the aggressive aerosol reductions in MTFR periods of poor visibility, represented by above-normal aerosol optical depth (AOD), still occur in conjunction with haze-favorable atmospheric circulation. However, the winter mean intensity of poor visibility decreases in MTFR, so that haze events are less dangerous in this scenario by 2050 compared to CLE and relative to the current baseline. This study reveals the competing effects of aerosol emission reductions on future haze events through their direct contribution to pollutant source and their influence on the atmospheric circulation. A compound consideration of these two impacts should be taken in future policy making.