Aerosol Measurements Research Articles

Submicron aerosol and nitrogen dioxide in the atmospheric near-surface layer at the Zvenigorod Scientific Station of the A. M. Obukhov Institute of Atmospheric Physics RAS: Thirty years of measurements

The paper presents results of measurements and trend analysis of the mass concentration of submicron aerosol and the NO2 content in the atmospheric surface layer at the Zvenigorod Scientific Station of the A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences. The station is located in a rural area of the western Moscow region. Aerosol concentration is determined by directional light scattering in a flow nephelometer. The NO2 content is measured spectrometrically by zenith-scattered solar radiation. Three decades of aerosol and NO2 measurements give a possibility to analyze long-term trends in near-surface aerosol and NO2. Seasonally dependent estimates of the aerosol trends are presented for three periods differing in character of aerosol variability: 1991–2002, 2003–2012, and 2013–2020. The common feature of the trends is a general decrease in the aerosol concentration. There are however significant interdecadal differences in the strength of the trends and in their seasonal dependence. The NO2 content in the near-surface layer undergoes a significant positive trend. The NO2 increase is likely associated with an increase in the population and human activity resulting, in particular, in the increase in motor traffic in the region. Effects of wind direction on aerosol and NO2 anomalies are also studied.

Mass concentration measurements of autumn bioaerosol using low-cost sensors in a mature temperate woodland free-air carbon dioxide enrichment (FACE) experiment: investigating the role of meteorology and carbon dioxide levels

Abstract. Forest environments contain a wide variety of airborne biological particles (bioaerosols), including pollen, fungal spores, bacteria, viruses, plant detritus, and soil particles. Forest bioaerosol plays a number of important roles related to plant and livestock health, human disease and allergenicity, and forest and wider ecology and are thought to influence biosphere–atmosphere interactions via warm and cold cloud formation. Despite the importance of bioaerosols, there are few measurements of forest aerosol, and there is a lack of understanding of how climate change will affect forest bioaerosol in the future. We installed low-cost optical particle counters (OPCs) to measure particles in the size range between 1 and 10 µm (PM10–PM1) for a period of 2 months in autumn 2018 at the Birmingham Institute of Forest Research (BIFoR) free-air carbon dioxide enrichment (FACE) facility. In the paper, we propose that the PM10–PM1 (particulate matter) metric is a good proxy for bioaerosols because of the bioaerosol representative size range, the location of the study site (a woodland in a rural location), the field measurement taking place during the season of peak fungal activity, and the low hygroscopicity of the particles measured. The BIFoR FACE facility fumigates three 700 m2 areas of the forest with an additional 150 ppm CO2 above ambient levels with minimal impacts on other potential environmental drivers such as temperature, humidity, and wind. This experimental set-up enabled us to investigate the effect of environmental variables, including elevated CO2 (eCO2), on bioaerosol proxy concentrations and to evaluate the performance of the low-cost OPCs in a forested environment. Operating the low-cost OPCs during autumn 2018, we aimed to capture predominantly the fungal bioaerosol season. Across the experimental duration, the OPCs captured both temporal and spatial variation in bioaerosol concentrations. Aerosol concentrations were affected by changing temperatures and wind speeds but, contrary to our initial hypothesis, not by relative humidity. We detected no effect of the eCO2 treatment on total bioaerosol concentrations, but a potential suppression of high-concentration bioaerosol events was detected under eCO2. In-canopy atmospheric dispersion modelling indicates that the median spore dispersion distance is sufficiently small that there is little mixing between treatment and control experiments. Our data demonstrate the suitability of low-cost OPCs, interpreted with due caution, for use in forests and so opens the possibility of forest bioaerosol monitoring in a wider range of habitats to a wider range of researchers at a modest cost.

Joint increase of aerosol scattering efficiency and aerosol hygroscopicity aggravate visibility impairment in the North China Plain

China's “Blue Sky Action Plan” aimed at tremendous improvements in atmospheric visibility. While stringent emission control policies have substantially brought down PM2.5 mass concentrations, visibility improved much less than expected due to non-linear responses of visibility changes to PM2.5 reductions. In this study, we used long-term continuous humidified nephelometer system measurements of multi-wavelength aerosol scattering coefficients in both dry state and controlled relative humidity conditions in the North China Plain during spring and summer to attempt disentanlge the non-linear relationsips between visibility and PM2.5 mass.Aerosol scattering efficiency, optical hygroscopicity and air relative humidity are key factors for relating PM2.5 mass to visibility. It was found that aerosol volume scattering efficiencies (VSEs) were highly correlated (r > 0.8) with aerosol scattering coefficients. The continuous decrease of aerosol scattering Ångström exponent during pollution episodes revealed dominant contributions of secondary aerosol formation to aerosol size growth and mass accumulation, explaining aerosol VSE increases. Moreover, the optical hygroscopicity parameter κsca that describes the aerosol light scattering enhancement abilities through water uptake increased jointly with VSE and aggravated the visibility degradation during middle to final stages of pollution episodes. Thus, low visibility events (<3 km) only occurred when VSE and κsca were at their highest levels. The contribution of aerosol water to visibility degradation increased as visibility decreased, and contributed dominantly to visibility degradation under extremely low visibility conditions (<1 km). However, under hazy visibility conditions (3–10 km), which occurred most frequently, both aerosol water and scattering efficiency enhancement played significant roles. For setting up more efficient emission control strategies targeting on visibility improvement, our results highly encourage more future research on the linkages between secondary aerosol formation mechanisms and co-variations of aerosol scattering efficiency and aerosol hygroscopicity on the NCP.

Development, verification and application of a versatile aerosol calibration system for online aerosol instruments

Traditional calibration methods mostly focus on the calibration of detection systems while the calibration from the sampling and pre-condition systems to the detection system is usually ignored. In this regard, a Primary Standard Aerosol Mass Concentration Calibration System (PAMAS) is developed for the whole-process calibration of time-resolved aerosol measurement instruments. PAMAS is composed of a particle generation chamber, an ultrasonic atomizer, a dilution system, and a syringe pump. It is designed to steadily generate standard aerosol particles of known concentrations (≤250 μg/m3), chemical compositions, and stable particle size distributions. Monodispersed aerosol can be generated in the size range of hundreds of nanometers to several micrometers with a narrow size distribution. The generated particles with different compositions generated by PAMAS have been well verified by the filter-based gravimetric method, yielding accuracy and R2 of more than 95% and 0.999 in a wide concentration range. The response time by changing the target concentration of reference particles is 1–2 min. PAMAS has been applied to various types of time-resolved aerosol measurement instruments, including particle mass concentration monitors (Beta Attenuation and Tapered Element Oscillating Microbalance), online Ion Chromatograph, and semi-continuous OCEC carbon aerosol analyzer. Very consistent results between PAMAS and calibrated instruments can be obtained if the instruments are functioning well. As for instruments with certain technical issues, PAMAS can serve as a good tool for performance evaluation and quality assurance of the instruments and the accuracy of the measurement data can be adjusted based on the calibration results.

PM2.5 in Carlsbad Caverns National Park: Composition, sources, and visibility impacts

ABSTRACT Carlsbad Caverns National Park in southeastern New Mexico is adjacent to the Permian Basin, one of the most productive oil and gas regions in the country. The 2019 Carlsbad Caverns Air Quality Study (CarCavAQS) was designed to examine the influence of regional sources, including urban emissions, oil and gas development, wildfires, and soil dust on air quality in the park. Field measurements of aerosols, trace gases, and deposition were conducted from 25 July through 5 September 2019. Here, we focus on observations of fine particles and key trace gas precursors to understand the important contributing species and their sources and associated impacts on haze. Key gases measured included aerosol precursors, nitric acid and ammonia, and oil and gas tracer, methane. High-time resolution (6-min) PM2.5 mass ranged up to 31.8 µg m−3, with an average of 7.67 µg m−3. The main inorganic ion contributors were sulfate (avg 1.3 µg m−3), ammonium (0.30 µg m−3), calcium (Ca2+) (0.22 µg m−3), nitrate (0.16 µg m−3), and sodium (0.057 µg m−3). The WSOC concentration averaged 1.2 µg C m−3. Sharp spikes were observed in Ca2+, consistent with local dust generation and transport. Ion balance analysis and abundant nitric acid suggest PM2.5 nitrate often reflected reaction between nitric acid and sea salt, forming sodium nitrate, and between nitric acid and soil dust containing calcium carbonate, forming calcium nitrate. Sulfate and soil dust are the major contributors to modeled light extinction in the 24-hr average daily IMPROVE observations. Higher time resolution data revealed a maximum 1-hr extinction value of 90 Mm−1 (excluding coarse aerosol) and included periods of significant light extinction from BC as well as sulfate and soil dust. Residence time analysis indicated enrichment of sulfate, BC, and methane during periods of transport from the southeast, the direction of greatest abundance of oil and gas development. Implications: Rapid development of U.S. oil and gas resources raises concerns about potential impacts on air quality in National Parks. Measurements in Carlsbad Caverns National Park provide new insight into impacts of unconventional oil and gas development and other sources on visual air quality in the park. Major contributors to visibility impairment include sulfate, soil dust (often reacted with nitric acid), and black carbon. The worst periods of visibility and highest concentrations of many aerosol components were observed during transport from the southeast, a region of dense Permian Basin oil and gas development.

Volcanic Eruption of Cumbre Vieja, La Palma, Spain: A First Insight to the Particulate Matter Injected in the Troposphere

The volcanic eruption of Cumbre Vieja (La Palma Island, Spain), started on 19 September 2021 and was declared terminated on 25 December 2021. A complete set of aerosol measurements were deployed around the volcano within the first month of the eruptive activity. This paper describes the results of the observations made at Tazacorte on the west bank of the island where a polarized micro-pulse lidar was deployed. The analyzed two-and-a-half months (16 October–31 December) reveal that the peak height of the lowermost and strongest volcanic plume did not exceed 3 km (the mean of the hourly values is 1.43 ± 0.45 km over the whole period) and was highly variable. The peak height of the lowermost volcanic plume steadily increased until week 11 after the eruption started (and 3 weeks before its end) and started decreasing afterward. The ash mass concentration was assessed with a method based on the polarization capability of the instrument. Two days with a high ash load were selected: The ash backscatter coefficient, aerosol optical depth, and the volume and particle depolarization ratios were, respectively, 3.6 (2.4) Mm−1sr−1, 0.52 (0.19), 0.13 (0.07) and 0.23 (0.13) on 18 October (15 November). Considering the limitation of current remote sensing techniques to detect large-to-giant particles, the ash mass concentration on the day with the highest ash load (18 October) was estimated to have peaked in the range of 800–3200 μg m−3 in the lowermost layer below 2.5 km.

Real-time detection of vehicle-originated condensable particulate matter through thermodenuder integrated aerosol measurement method at tailpipes

Condensable particulate matter (CPM) corresponds to primary particulate matter ≤2.5 μm (PM2.5) obtained through the condensation of gaseous air pollutants caused by temperature drops in the atmosphere. The internal combustion of vehicle engines can produce CPM because of the condensable compounds in the exhaust gas. Conventional CPM measurement methods have been developed for coal-fired power plants with stable emissions through sampling and off-site analyses. They are therefore unsuitable for detecting the rapidly changing vehicle-originated CPM. In addition, the current system for evaluating PM2.5 from vehicles, based on the particle measurement program (PMP) protocol, provides only the emission factors of total PM2.5 (and not CPM separately) at a fixed temperature (∼25 °C) and dilution ratio (∼ × 35). This study reports, for the first time, the development of a real-time detection method for vehicle-originated CPM through a thermodenuder (TD) integrated with real-time aerosol instruments. This method was designed to reduce the loss of CPM due to condensation and diffusion while sampling the exhaust gas. It permits the investigation of the effects of dilution gas temperature (5–45 °C) and dilution ratio (up to × 30) on the formation of CPM. During the feasibility test of this method using a diesel vehicle (Euro-4), the real-time total particle number concentrations (PNs) matched well with those obtained by a PMP protocol-based evaluation system. Moreover, this method detected PNs concentrations ten times higher than the detection limit (4 × 106 particles/cm3) of the PMP-based system. The emission factors of the total PM2.5 with a bulk density (1 g/cm3) measured by this method also showed consistency with the results of the PMP protocol. The mass emission factor of CPM determined by deploying the TD was ∼14.57 mg/km (∼63% contribution to the total PM2.5).

New particle formation in coastal New Zealand with a focus on open-ocean air masses

Abstract. Even though oceans cover the majority of the Earth, most aerosol measurements are from continental sites. We measured aerosol particle number size distribution at Baring Head, in coastal New Zealand, over a total period of 10 months to study aerosol properties and new particle formation, with a special focus on aerosol formation in open-ocean air masses. Particle concentrations were higher in land-influenced air compared to clean marine air in all size classes, from sub-10 nm to cloud condensation nuclei sizes. When classifying the particle number size distributions with traditional methods designed for continental sites, new particle formation was observed at the station throughout the year with an average event frequency of 23 %. While most of these traditional event days had some land influence, we also observed particle growth starting from nucleation mode in 16 % of the data in clean marine air, and at least part of this growth was connected to nucleation in the marine boundary layer. Sub-10 nm particles accounted for 29 % of the total aerosol number concentration of particles larger than 1 nm in marine air during the spring. This shows that nucleation in marine air is frequent enough to influence the total particle concentration. Particle formation in land-influenced air was more intense and had on average higher growth rates than what was found for marine air. Particle formation and primary emissions increased particle number concentrations as a function of time spent over land during the first 1–2 d. After this, nucleation seems to start getting suppressed by the pre-existing particle population, but accumulation mode particle concentration keeps increasing, likely due to primary particle emissions. Further work showed that traditional NPF events were favoured by sunny conditions with low relative humidity and wind speeds. In marine air, formation of sub-10 nm particles was favoured by low temperatures, relative humidity, and wind speeds and could happen even during the night. Our future work will study the mechanisms responsible for particle formation at Baring Head with a focus on different chemical precursor species. This study sheds light on both new particle formation in open-ocean air masses coming from the Southern Ocean and local aerosol properties in New Zealand.

Characterization of Wildfire Smoke over Complex Terrain Using Satellite Observations, Ground-Based Observations, and Meteorological Models

The severity of wildfires is increasing globally. In this study, we used data from the Global Change Observation Mission-Climate/Second-generation Global Imager (GCOM-C/SGLI) to characterize the biomass burning aerosols that are generated by large-scale wildfires. We used data from the September 2020 wildfires in western North America. The target area had a complex topography, comprising a basin among high mountains along a coastal region. The SGLI was essential for dealing with the complex topographical changes in terrain that we encountered, as it contains 19 polarization channels ranging from near ultraviolet (380 nm and 412 nm) to thermal infrared (red at 674 nm and near-infrared at 869 nm) and has a fine spatial resolution (1 km). The SGLI also proved to be efficient in the radiative transfer simulations of severe wildfires through the mutual use of polarization and radiance. We used a regional numerical model SCALE (Scalable Computing for Advanced Library and Environment) to account for variations in meteorological conditions and/or topography. Ground-based aerosol measurements in the target area were sourced from the National Aeronautics and Space Administration-Aerosol Robotic Network; currently, official satellite products typically do not provide the aerosol properties for very optically thick cases of wildfires. This paper used satellite observations, ground-based observations, and a meteorological model to define an algorithm for retrieving the aerosol properties caused by severe wildfire events.

Assessing the Impact of Atmospheric CO2 and NO2 Measurements From Space on Estimating City-Scale Fossil Fuel CO2 Emissions in a Data Assimilation System

The European Copernicus programme plans to install a constellation of multiple polar orbiting satellites (Copernicus Anthropogenic CO2 Monitoring Mission, CO2M mission) for observing atmospheric CO2 content with the aim to estimate fossil fuel CO2 emissions. We explore the impact of potential CO2M observations of column-averaged CO2 (XCO2), nitrogen dioxide (NO2), and aerosols in a 200 × 200 km2 domain around Berlin. For the quantification of anticipated XCO2 random and systematic errors we developed and applied new error parameterisation formulae based on artificial neural networks. For the interpretation of these data, we further established a CCFFDAS modelling chain from parameters of emission models to XCO2 and NO2 observations to simulate the 24 h periods preceeding simulated CO2M overpasses over the study area. For one overpass in winter and one in summer, we present a number of assessments of observation impact in terms of the posterior uncertainty in fossil fuel emissions on scales ranging from 2 to 200 km. This means the assessments include temporal and spatial scales typically not covered by inventories. The assessments differentiate the fossil fuel CO2 emissions into two sectors, an energy generation sector (power plants) and the complement, which we call “other sector.” We find that combined measurements of XCO2 and aerosols provide a powerful constraint on emissions from larger power plants; the uncertainty in fossil fuel emissions from the largest three power plants in the domain was reduced by 60%–90% after assimilating the observations. Likewise, these measurements achieve an uncertainty reduction for the other sector that increases when aggregated to larger spatial scales. When aggregated over Berlin the uncertainty reduction for the other sector varies between 28% and 48%. Our assessments show a considerable contribution of aerosol observations onboard CO2M to the constraint of the XCO2 measurements on emissions from all power plants and for the other sector on all spatial scales. NO2 measurements onboard CO2M provide a powerful additional constraint on the emissions from power plants and from the other sector. We further apply a Jacobian representation of the CCFFDAS modelling chain to decompose a simulated CO2 column in terms of spatial emission impact. This analysis reveals the complex structure of the footprint of an observed CO2 column, which indicates the limits of simple mass balances approaches for interpretation of such observations.

Wildfire Smoke Observations in the Western United States from the Airborne Wyoming Cloud Lidar during the BB-FLUX Project. Part I: Data Description and Methodology

Abstract During the summer of 2018, the upward-pointing Wyoming Cloud Lidar (WCL) was deployed on board the University of Wyoming King Air (UWKA) research aircraft for the Biomass Burning Flux Measurements of Trace Gases and Aerosols (BB-FLUX) field campaign. This paper describes the generation of calibrated attenuated backscatter coefficients and aerosol extinction coefficients from the WCL measurements. The retrieved aerosol extinction coefficients at the flight level strongly correlate (correlation coefficient, rr &gt; 0.8) with in situ aerosol concentration and carbon monoxide (CO) concentration, providing a first-order estimate for converting WCL extinction coefficients into vertically resolved CO and aerosol concentration within wildfire smoke plumes. The integrated CO column concentrations from the WCL data in nonextinguished profiles also correlate (rr = 0.7) with column measurements by the University of Colorado Airborne Solar Occultation Flux instrument, indicating the validity of WCL-derived extinction coefficients. During BB-FLUX, the UWKA sampled smoke plumes from more than 20 wildfires during 35 flights over the western United States. Seventy percent of flight time was spent below 3 km above ground level (AGL) altitude, although the UWKA ascended up to 6 km AGL to sample the top of some deep smoke plumes. The upward-pointing WCL observed a nearly equal amount of thin and dense smoke below 2 km and above 5 km due to the flight purpose of targeted fresh fire smoke. Between 2 and 5 km, where most of the wildfire smoke resided, the WCL observed slightly more thin smoke than dense smoke due to smoke spreading. Extinction coefficients in dense smoke were 2–10 times stronger, and dense smoke tended to have larger depolarization ratio, associated with irregular aerosol particles.

Effects of nanosized water droplet generation on number concentration measurement of virus aerosols when using an airblast atomizer

Development of efficient virus aerosol monitoring and removal devices requires aerosolization of the test virus using atomizers. The number concentration and size measurements of aerosolized virus particles are required to evaluate the performance of the devices. Although diffusion dryers can remove water droplets generated using atomizers, they often fail to remove them entirely from the air stream. Consequently, particle measurement devices, such as scanning mobility particle sizer (SMPS), can falsely identify the remaining nanosized water droplets as virus aerosol particles. This in turn affects the accuracy of the evaluation of devices for sampling or removing virus aerosol particles. In this study, a plaque-forming assay combined with SMPS measurement was used to evaluate sufficient drying conditions. We proposed an empirical equation to determine the total number concentration of aerosolized particles measured using the SMPS as a function of the carrier air flow rate and residence time of the particles in the diffusion dryers. The difference in the total number concentration of particles under sufficient and insufficient diffusion drying conditions was presented as a percentage of error.

Comparison of aerosol mitigation strategies and aerosol persistence in dental environments.

To determine the impact of various aerosol mitigation interventions and to establish duration of aerosol persistence in a variety of dental clinic configurations. We performed aerosol measurement studies in endodontic, orthodontic, periodontic, pediatric, and general dentistry clinics. We used an optical aerosol spectrometer and wearable particulate matter sensors to measure real-time aerosol concentration from the vantage point of the dentist during routine care in a variety of clinic configurations (eg, open bay, single room, partitioned operatories). We compared the impact of aerosol mitigation strategies (eg, ventilation and high-volume evacuation (HVE), and prevalence of particulate matter) in the dental clinic environment before, during, and after high-speed drilling, slow-speed drilling, and ultrasonic scaling procedures. Conical and ISOVAC HVE were superior to standard-tip evacuation for aerosol-generating procedures. When aerosols were detected in the environment, they were rapidly dispersed within minutes of completing the aerosol-generating procedure. Few aerosols were detected in dental clinics, regardless of configuration, when conical and ISOVAC HVE were used. Dentists should consider using conical or ISOVAC HVE rather than standard-tip evacuators to reduce aerosols generated during routine clinical practice. Furthermore, when such effective aerosol mitigation strategies are employed, dentists need not leave dental chairs fallow between patients because aerosols are rapidly dispersed.

The Aerosol Research Observation Station (AEROS)

Abstract. Information on atmospheric particles' concentration and sizes is important for environmental and human health reasons. Air quality monitoring stations (AQMSs) for measuring particulate matter (PM) concentrations are found across the United States, but only three AQMSs measure PM2.5 concentrations (mass of particles with an aerodynamic diameter of &lt; 2.5 µm) in the Southern High Plains of West Texas (area ≥ 1.8 × 105 km2). This area is prone to many dust events (∼ 21 yr−1), yet no information is available on other PM sizes, total particle number concentration, or size distribution during these events. The Aerosol Research Observation Station (AEROS) was designed to continuously measure these particles' mass concentrations (PM1, PM2.5, PM4, and PM10) and number concentrations (0.25–35.15 µm) using three optical particle sensors (Grimm 11-D, OPS, and DustTrak) to better understand the impact of dust events on local air quality. The AEROS aerosol measurement unit features a temperature-controlled shed with a dedicated inlet and custom-built dryer for each of the three aerosol instruments used. This article provides a description of AEROS as well as an intercomparison of the different instruments using laboratory and atmospheric particles. Instruments used in AEROS measured a similar number concentration with an average difference of 2 ± 3 cm−1 (OPS and Grimm 11-D using similar particle size ranges) and a similar mass concentration, with an average difference of 8 ± 3.6 µg m−3 for different PM sizes between the three instruments. Grimm 11-D and OPS had a similar number concentration and size distribution, using a similar particle size range and similar PM10 concentrations (mass of particles with an aerodynamic diameter of &lt; 10 µm). Overall, Grimm 11-D and DustTrak had good agreement in mass concentration, and comparison using laboratory particles was better than that with atmospheric particles. Overall, DustTrak measured lower mass concentrations compared to Grimm 11-D for larger particle sizes and higher mass concentrations for lower PM sizes. Measurement with AEROS can distinguish between various pollution events (natural vs. anthropogenic) based on their mass concentration and size distribution, which will help to improve knowledge of the air quality in this region.

Aerosol pool scrubbing phenomena during the containment depressurization venting. Part Ⅱ: Test facility and test result

To verify the feasibility of aerosol scrubbing with Spent Fuel Pool (SFP) during the containment depressurization venting process, the China Aerosol Spent fuel pool Scrubbing Integrated (CASSI) test facility has been designed and built. The CASSI consists of the gas supply system, heating and insulation system, data measurement and acquisition system, aerosol generation system, and aerosol sampling and measurement system. In this study, the current status of the CASSI is introduced along with a description of the aerosol generation system and aerosol sampling and measurement system. A verification test has been carried out, and the test results are described in detail, which shows that the CASSI has good thermo-hydraulic stability and the scrubbing efficiency of solid particles is more than 99.8%. The scrubbing efficiency of particles with diameter greater than 1.08 μm is more than 99.9% during pool scrubbing. The test results proved the feasibility of aerosol scrubbing with SFP.

Primary Emissions and Secondary Aerosol Processing During Wintertime in Rural Area of North China Plain

AbstractThe vast rural areas often experience more severe haze pollution than megacities during wintertime in North China Plain (NCP), yet the sources and evolution processes of aerosol particles, particularly organic aerosol (OA) remain poorly understood. Here we conducted real‐time measurements of submicron aerosol (PM1) species using a high‐resolution aerosol mass spectrometer at a representative rural site in NCP in winter 2019. Our results showed the dominance of organics (36%) and nitrate in PM1 (22%) in 2019. Positive matrix factorization analysis illustrated similarly important primary sources from traffic emissions, coal combustion, and biomass burning, yet secondary OA (SOA) from photochemical and aqueous‐phase related processing exceeded primary OA (53% vs. 47%). Substantial decreases in primary species and considerable increases in nitrate and sulphate were observed since winter 2018, demonstrating enhanced secondary formation in winter 2019. OA composition changed significantly from clean period to fog events with the contribution of aqueous phase‐related oxygenated OA increasing from 6% to 44%, while the photochemical SOA decreased correspondingly from 51% to 19%. The size distributions of aerosol species also changed by shifting toward large sizes during fog events. Elemental analysis of OA and the Van Krevelen diagram (H/C vs. O/C) illustrated the different roles of photochemical and aqueous‐phase processing during daytime and nighttime, respectively, and aqueous‐phase processing is subject to the formation of organic compounds with high H/C and O/C ratios. The large differences in fog processing of submicron aerosol species between 2018 and 2019 due to different temperatures were also elucidated.

Experimental and analytical investigations on aerosol washout in a large vessel with high spray coverage ratio simulating PWR containment spray

ABSTRACT In severe accident scenarios of a PWR, containment spray can be employed to washout the aerosol of radioactive materials, retaining them in the containment. Therefore, it is crucial to correctly predict the aerosol washout efficiency for safety assessment. For a PWR containment, a high spray coverage ratio (>84%–95%) is required. However, experimental studies focusing on the washout efficiency with such a high coverage ratio in a large vessel are quite limited. To understand such a washout phenomenon toward model development, specifically for PWR, aerosol washout experiments are performed in a large vessel with not only aerosol measurements but also spray droplet characterizations. Significant droplet impaction on the vessel sidewall is observed, and the spray coverage ratios are experimentally confirmed to be compatible with a real PWR. The washout features are investigated in terms of individual particle diameters and the entire one. The model in the safety analysis code, MELCOR, is examined using the experimentally obtained aerosol removal rate, showing the removal rate tendency against particle diameters being reproduced. Although a significant underestimation occurs for large particles, a satisfactory agreement is obtained for smaller ones (<0.52 μm in diameter) corresponding to the minimum removal rate and around.

Ground-Based MAX-DOAS Measurements of Tropospheric Aerosols, NO2, and HCHO Distributions in the Urban Environment of Shanghai, China

Aerosol extinction profiles at 550 nm were retrieved by applying multi-axis differential optical absorption spectroscopy (MAX-DOAS) and lookup table. Then the tropospheric NO2 and HCHO vertical column densities were retrieved using a two-step method from 28 July to 5 August of 2015 in Shanghai. The retrieved results were compared with the satellite products, and then their diurnal variation was observed. A consistency check was performed before the inversion to obtain a correction factor. Based on the sensitivity of geometric angles to oxygen dimer air mass factor (O4 AMF, AMF is the ratio of the slanted column density to the vertical column density), the parameterization scheme of geometric angles in the lookup table is optimized. The results show that the aerosol increased significantly in the afternoon. The diurnal variation of tropospheric NO2 and HCHO vertical column densities (VCDs) are bimodal and unimodal patterns respectively, and their values are higher than those of GOME-2 and OMI satellite products. A process of aerosol reduction and recovery are related to ground particulates and meteorological elements. The chemical sensitivity of local ozone production also has a clear diurnal variation.

Flow visualization and aerosols in performance

The COVID-19 pandemic has created a great deal of fear and uncertainty around whether aerosols from singers and musical instruments can transmit the virus. The World Health Organization has recognized that SARS-COV-2 is transmissible through aerosols. Outbreaks from choir performances, such as the Skagit Valley Choir, showed that singing brings potential risk of COVID-19 infection. Additionally, outbreaks from singing have resulted in superspreader events leading to many infections and deaths. There is less known about the risks of airborne infection from other musical performance, such as playing wind instruments or performing theater. Hence, aerosol generation in performance (playing brass and woodwind instruments, singing, and theater speech delivery) should be quantified, monitored, and mitigated. To tackle this issue our research questions were as follows: (i) What is the aerosol generation rate? (ii) How does air flow from the performer’s mouth/instrument and how does it disseminate into the environment? and (iii) What control methods can be employed to mitigate risk? In this study, we used a variety of methods, including flow visualization, aerosol and CO2 measurements, and computational fluid dynamics (CFD) modeling to understand the different components that can lead to transmission risk from musical performance and risk mitigation.

EXTREME METHOD FOR SOLAR PHOTOMETERS CALIBRATION

Solar photometers are currently one of the main meteorological instruments with which the optical thickness of atmospheric aerosol and the total amount of water vapor in the atmosphere can be measured. These devices are also functionally suitable for estimating the total amount of ozone in the atmosphere, which confirms the importance of solar photometers for meteorological science. At present, aerosol measurement networks based on such devices are being built everywhere. The most important condition for the normal functioning of a solar photometer is the accurate calibration of this device. The article is devoted to the development of a new method of calibration of solar photometers, in which the influence of atmospheric aerosol instability is almost completely eliminated. It is shown that the total calibration error of solar photometers consists of two components: (a) the error caused by the instability of atmospheric aerosol; (b) the error of the geometric construction of the Langley diagram. The first of these components is practically considered unrecoverable by existing methods, and the second can be eliminated using previously proposed computational methods. The developed extreme method of calibration of solar photometers eliminates the need to construct a Langley diagram for several hours, during which the atmospheric aerosol, due to its variability, introduces a significant error in the calibration result. Thus, the main drawback of the classical Langley method is eliminated. The effect of increasing the accuracy of calibration is achieved by forming an additional informative indicator and further investigation of the extremum of this newly introduced indicator. Quantitative indicators of the achieved effect of increasing accuracy are given. As an example, it is shown that despite some high duration of implementation of the proposed method, it becomes possible to eliminate the aerosol error of 2.74 % that occurs when the optical thickness of the atmosphere is less than 0.1, and when this indicator is unstable by 10 percent during the implementation of the Langley method. The functional optical scheme of the device and the algorithm for implementing the proposed calibration method are given.