Coarse Mode Particles Research Articles

Mass and number concentration distribution of marine aerosol in the Western Pacific and the influence of continental transport

We quantify for the first time marine aerosol properties and their differences in the offshore and remote ocean in the mid-latitude South Asian waters, low-latitude South Asian waters, and equatorial waters of the Western Pacific Ocean, based on shipboard cruise observations conducted by the Western Pacific Ocean Scientific Observation Network in winter 2018, and further investigate the effects of long-range transport of continental aerosols on the marine environment. During the overall observation period, the average number concentration of particle matter which aerodynamic diameters<2.5 μm (PM2.5N) was 35.1 ± 87.4 cm−3 and the mass concentration (PM2.5M) was 12.3 ± 9.1 μg/m3. The PM2.5N and PM2.5M during the continental air mass transport period were 7.2 and 1.3 times higher than those during the non-transport period (109.2 ± 169.3 cm−3, 15.9 ± 14.9 μg/m3), respectively. Excluding transport period, the average PM2.5N and PM2.5M are reduced by 120% and 7%. Coarse mode particle number concentration (PM2.5–10N) and mass concentration (PM2.5–10M) are not significantly influenced by continental air masses (only a reduction of 7% and 2%). The variation of marine aerosol concentrations in different latitudes zones is greatly influenced by continental aerosol transport. The offshore PM2.5M/PM10M was 30%, 21%, and 22% in the mid-latitude sea of South Asia, a low-latitude sea of South Asia, and the equatorial sea, respectively. In comparison, in the remote ocean, the distribution ratio of PM2.5M/PM10M tended to be steady (22%–23%), and the background characteristics of marine aerosols were clearly represented. The aerosol concentration decreases with the increase of wind speed during the transport period, and the wind speed reflects the scavenging effect on aerosol. In the non-transport period, the wind speed at the sea surface promotes the generation of marine aerosols, and the impact in wind speed is strongest in the PM2.5–PM5 particle size range.

Off-season lee wave cloud over the Arsia Mons in Mars: A study based on Mars Colour Camera (MCC)

The present analysis reported the lee wave interpretation on Arsia Mons Elongated Cloud (AMEC) that used to appear over the lee side of the Arsia Mons. The present work also reported the wavelength, the cloud's height, and wind speed of the observed lee wave structure. The estimated wind speed is 86 ± 4.9 m/s, with a wavelength of 60 ± 0.3 km at an altitude of 55 ± 7 km. This is the largest lee wave structure that appears during the dust storm season (Ls = 230 to Ls = 300) and strongly contributes to the planet's Albedo level. Calculated TOA reflectance varies from 0.05 to 0.15 for the blue channel and 0.02 to 0.09 for the red channel. Estimated AOD ranges from 1.8 (red channel) to 1.5 (blue channel), indicating the contribution of dust and water ice crystal. The estimated angstrom exponent (α) value signifies coarse mode particle presence in the cloud with an effective radius of 3.2 μm. The presence of water ice crystal contributes to the albedo level's increment to 0.8 and signifies the formation temperature for AMEC to be around 190 K.

A New Instrument for Determining the Coarse-Mode Sea Salt Aerosol Size Distribution

AbstractSea salt aerosol (SSA) plays a significant role in the atmosphere through aerosol direct and indirect effects, and in atmospheric chemistry as a source of tropospheric bromine. In situ measurements of coarse-mode SSA particles are limited because of their low concentration and relatively large sizes (dry radius rd &gt; 0.5 μm). With this in mind, a new, low-cost, easily usable method for sampling coarse-mode SSA particles in the marine boundary layer was developed. An SSA particle sampler that uses an impaction method was designed and built using 3D printing and Arduino microcontrollers and sensors. It exposes polycarbonate slides to ambient airflow remotely on a kite-based platform to capture coarse-mode SSA particles. Because it is a smaller version of the Giant Nucleus Impactor (GNI), designed for use on aircraft, it is named the miniature Giant Nucleus Impactor (miniGNI). After sample collection, the same optical microscope methodology utilized by the GNI was used to analyze the wetted salt particles that impacted onto the slides. In this proof-of-concept study, multiple miniGNIs were attached serially to a kite string, allowing for sampling at multiple altitudes simultaneously. The robustness of the results from this new instrument and methodology for sampling at ambient RH (~75%) the SSA particle size distribution with rd &gt; 3.3 μm are compared with a similar study. We find that the SSA particle number concentration decreases weakly with altitude and shows no correlation to instantaneous U10 wind speed along the windward coastline of Oʻahu in the Hawaiian Islands.

Classification of aerosol types using AERONET version 3 data over Kuwait City

The particle linear depolarization ratio (PLDR) and single scattering albedo (SSA) at 1020 nm are retrieved by the AERONET (Aerosol Robotic Network) Version 3.0 level 1.5 inversion products are used to categorize different types of aerosols and investigate their temporal distribution for the atmospheric particles of Kuwait City. The results show that when PLDR increases in the atmosphere, the amount of SSA at 440, 670, 870, and 1020 nm wavelength channels and the contribution of coarse-mode particles increased. Also, the spectral behavior of SSA changes from a negative to positive slope by increasing PLDR. The highest density of aerosol incidence rate in the two-dimensional histogram diagram occurs in the range with low fine mode fraction and dust ratio. The main objective of this study is to present that the atmosphere of Kuwait City is strongly affected by pure dust (PD) and polluted dust plumes, namely, dust-dominated mixture (DDM), pollution dominated mixture (PDM), all with an occurrence frequency of 85%. The annual average incidence rate of different aerosol types is 32.2% for DDM, 31% for PD, 21.8% for PDM, 10.3% for SA, 2.5% for MA, 1.3% for WA, and 0.9% for NA, from 2006 to 2019. However, the distribution of different types of pollution particles varies with the seasons change. The incidence rate of pure and polluted dust is more than 85% from March to October. In addition, the annual average incidence rate of dust-free pollution aerosols (NA, WA, MA, and SA) is 15%. The highest amount of dust-free pollution particles in different months is related to the SA that constitutes about 40% in the cold months.

Overview and Seasonality of PM10 and PM2.5 in Guayaquil, Ecuador

The focus of this study is the assessment of total suspended particles (TSP) and particulate matter (PM) with various aerodynamic diameters in ambient air in Guayaquil, a city in Ecuador that features a tropical climate. The urban annual mean concentrations of TSP (Total Suspended Particles), and particle matter (PM) with various aerodynamic diameters such as: PM10, PM2.5 and PM1 are 31 ± 14 µg m−3, 21 ± 9 µg m−3, 7 ± 2 µg m−3 and 1 ± 1 µg m−3, respectively. Air mass studies reveal that the city receives a clean Southern Ocean breeze. Backward trajectory analysis show differences between wet and dry seasons. During the dry season, most winds come from the south and southwest, while air masses from the peri urban may contribute as pollutant sources during the wet season. Although mean values of PM10 and PM2.5 were below dangerous levels, our year-round continuous monitoring study reveals that maximum values often surpassed those permissible limits allowed by the Ecuadorian norms. A cluster analysis shows four main paths in which west and southwest clusters account for more than 93% of the pollution. Total vertical column of NO2 shows the pollution footprint is strongest during the dry season, as opposed to the wet season. A microscopic morphological characterization of ambient particles within the city during the wet and the dry season reveals coarse mode particles with irregular and rounded shapes. Particle analysis reveals that samples are composed of urban dust, anthropogenic and organic debris during the dry season while mainly urban dust during the wet season.

Impacts of the Variations of Aerosols Components and Relative Humidity on the Visibility and Particles Size Distribution of the Desert Atmosphere

This paper investigates the Impact of relative humidity, varying the concentrations of water-soluble aerosol particle concentrations (WASO), Mineral Nuclei Mode Aerosols Particle Concentration (MINN), mineral accumulation mode, nonspherical (MIAN) aerosol particles concentrations and Mineral Coarse Mode Aerosols Particle Concentration (MICN) on the visibility and particles size distribution of desert aerosols based on microphysical properties of desert aerosols. The microphysical properties (the extinction coefficients, volume mix ratios, dry mode radii and wet mode radii) were extracted from Optical Properties of Aerosols and Clouds (OPAC 4.0) at eight relative humidities, RHs (00 to 99%) and at the spectral visible range of 0.4-0.8mm, the concentrations were varied to obtain five different models for each above-mentioned component. Regression analysis of some standard equations were used to determine the Angstrom exponent (α), the turbidity coefficient (β), the curvature (α2), humidification factor (), the mean exponent of aerosol growth curve (µ) and the mean exponent of aerosol size distributions (n). The values of angstrom exponent (α) were observed to be less than 1 throughout the five models at all RHs for the four studied components, and this signifies the dominance of coarse mode particles over fine mode particles. But the magnitude of the angstrom exponent (α) fluctuates all through the studied components except for WASO which increased with the increase in RH across the models and this also signifies the dominance of coarse mode particles with some traces of fine mode particles. The investigation also revealed that the curvature (α2) has both monomodal (negative signs) and bimodal (positive signs) types of distributions all through the five models and this also signifies the dominance of coarse mode particles with some traces of fine mode particles across the individual models for all the studied components. it was also found that the visibility decreased with the increase in RH and increased with the increase in wavelength. The investigation further revealed that the turbidity coefficient (β) fluctuates with the increase in RH and the particles concentrations, and this might be due to major coagulation and sedimentation. The analysis further found that there is a direct inverse power relation between the humidification factor and the mean exponent of aerosols size distribution with the mean exponent of aerosols growth curve. It was also found that as the magnitude of µ increased for MIAN, MINN and MICN, the effective hygroscopic growth decreased. For WASO, it was found that as the magnitude of µ decreased, the effective hygroscopic growth increased with the increase in particles concentrations and RH. The decreased in the magnitude of µ for WASO might be due to the fact that as we increase the non-hygroscopic particles, we decrease the deliquescence. The mean exponent of aerosol size distribution (n) being less than 3 shows foggy condition of the desert atmosphere the four investigated components and five studied models.

Evaluation of the offline-coupled GFSv15-FV3-CMAQv5.0.2 in support of the next-generation National Air Quality Forecast Capability over the contiguous United States.

As a candidate for the next-generation National Air Quality Forecast Capability (NAQFC), the meteorological forecast from the Global Forecast System with the new Finite Volume Cube-Sphere dynamical core (GFS–FV3) will be applied to drive the chemical evolution of gases and particles described by the Community Multiscale Air Quality modeling system. CMAQv5.0.2, a historical version of CMAQ, has been coupled with the North American Mesoscale Forecast System (NAM) model in the current operational NAQFC. An experimental version of the NAQFC based on the offline-coupled GFS–FV3 version 15 with CMAQv5.0.2 modeling system (GFSv15–CMAQv5.0.2) has been developed by the National Oceanic and Atmospheric Administration (NOAA) to provide real-time air quality forecasts over the contiguous United States (CONUS) since 2018. In this work, comprehensive region-specific, time-specific, and categorical evaluations are conducted for meteorological and chemical forecasts from the offline-coupled GFSv15–CMAQv5.0.2 for the year 2019. The forecast system shows good overall performance in forecasting meteorological variables with the annual mean biases of −0.2 °C for temperature at 2 m, 0.4% for relative humidity at 2 m, and 0.4 m s−1 for wind speed at 10 m compared to the METeorological Aerodrome Reports (METAR) dataset. Larger biases occur in seasonal and monthly mean forecasts, particularly in spring. Although the monthly accumulated precipitation forecasts show generally consistent spatial distributions with those from the remote-sensing and ensemble datasets, moderate-to-large biases exist in hourly precipitation forecasts compared to the Clean Air Status and Trends Network (CASTNET) and METAR. While the forecast system performs well in forecasting ozone (O3) throughout the year and fine particles with a diameter of 2.5 μm or less (PM2.5) for warm months (May–September), it significantly overpredicts annual mean concentrations of PM2.5. This is due mainly to the high predicted concentrations of fine fugitive and coarse-mode particle components. Underpredictions in the southeastern US and California during summer are attributed to missing sources and mechanisms of secondary organic aerosol formation from biogenic volatile organic compounds (VOCs) and semivolatile or intermediate-volatility organic compounds. This work demonstrates the ability of FV3-based GFS in driving the air quality forecasting. It identifies possible underlying causes for systematic region- and time-specific model biases, which will provide a scientific basis for further development of the next-generation NAQFC.

A case study on the vertical distribution and characteristics of aerosols using ground-based raman lidar, satellite and model over Western India

ABSTRACT Ahmedabad is an urban site in western region of India. Dust loading and its variability are very high over this semi-arid location. A state-of-the-art ground-based Raman lidar has been used for the study of day-to-day variability in vertical distribution of aerosol loading over Ahmedabad (23.02° N, 72.57° E) from 8 to 11 May 2018. We have done a comprehensive study about vertical profiles of aerosols across two wavelengths recorded simultaneously, namely, 355 nm and 532 nm, over this location. An interesting hump feature has been noted on 9 May at around 18 h (Local Time), with an additional peak at 19 h on 10 May. The loading over this region has more fine-mode aerosols than coarse-mode particles. Further, findings from ground-based lidar have been compared with MACC-II model simulations and Cloud-Aerosol Lidar with Orthogonal Polarization on-board Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observational. Back-trajectory analysis showed majority of the influx came from middle-east, carrying mineral dust and traces of marine aerosols from Arabian Sea, except for 11 May, where low-level dust carrying trajectories and also coarser dust particles were not seen. This type of manifestation has also been observed while classifying aerosols over Ahmedabad using Lidar Depolarization Ratio and Lidar Ratio obtained from Raman Lidar. Fine mode aerosols have been characterized as industrial, vehicular and marine, while coarser as mineral dust and biomass burning. This study focuses on local variation and classification of aerosols based on size and type, which will further help in better estimation of radiative budget and other impacts of aerosols.

Temporal and Spatial Distribution Characteristics of Aerosol Optical Properties in Urban Agglomerations on the North Slope of the Tianshan Mountains

In order to explore the temporal and spatial distribution characteristics of atmospheric aerosol optical depth (AOD) in the urban agglomeration on the northern slope of the Tianshan Mountains, the temporal and spatial distribution characteristics and trends of changes in the AOD in the study area from 2000 to 2019 were analyzed by MODIS aerosol products(MCD19-A2). For 2016-2019, when the AOD was relatively stable, the parameters such as the AOD and Ångström wavelength index (α) were analyzed using multi-band sun photometer ground-based remote sensing technology. The results showed that ① the spatial distribution of AOD in the study area was consistent with the topography, and high values were mainly distributed in the low altitude area. The spatial distribution of AOD in the four seasons showed a strong seasonal change from spring (0.15±0.03) > autumn (0.14±0.03) > summer (0.14±0.02). ② In terms of time, the annual average AOD value of the study area was 0.12 from 2000 to 2019 with an annual growth rate of 1.03%, thereby showing an overall increasing trend. The annual variation in the monthly mean value of AOD was bimodal; the first and second peaks were in May and November. The main reason for the increase in AOD was the release and transmission of dust from natural sources and heating. ③ Under the influence of dust weather, the AOD changed sharply in spring, and the size and change range of aerosol particles were larger than those in summer. The high value of AOD in the study area was mainly affected by coarse mode particles. The moisture absorption growth of fine mode particles caused a fluctuation in the AOD, but it was not the cause of the high value of AOD.

Aerosol optical properties over Delhi during a dust event in summer 2014: plausible implications

Delhi experiences frequent dust storms during the pre-monsoon season. We studied one such event that occurred on May 30th, 2014 at New Delhi to understand the changes in the optical properties of aerosols. The present study utilizes the aerosol optical depth (AOD) from the ground and satellite measurements along with reanalysis data. The aerosol characteristics were examined during the pre-week and post-week of the dust storm event. The results show that AOD values reach ~ 1.0 in all the modes of measurements (i.e., sun photometer, MODIS, and MERRA-2) on the dust event day. MODIS-derived Aerosol Angstrom Exponent (AAE), which gradually decreases from 1.7 ± 0.3 to 1.1 ± 0.3, shows the presence of coarse mode particles during the event. The aerosol layer at an elevation from 1 to 2 km was observed using indigenously developed dual-polarization micro-pulse lidar (MPL) system during the dust event. The source of the dust during the storm was identified by the air mass back-trajectories analysis. The dust column mass density averaged 24 hourly at 850 hPa is 780 mg m−2 with a prevailing wind direction of west to east with wind speed of 11–13 ms−1. Shortwave aerosol direct radiative forcing (SWADRF) diurnally averaged at the top of the atmosphere (TOA), the atmosphere (ATM), and surface (SUR) are found to be − 10 W m−2, 27 W m−2, and − 37 W m−2, respectively. The heating rate was enhanced by 56% (from 0.16 to 0.25 K day−1) during the event in the whole atmospheric column. Visibility decreased by 31% during the dust storm day compared with its average value of non-dust storm days.

Characteristics of fine particle formation during combustion of Xinjiang high-chlorine-sodium coal

Shaerhu (SEH) coal in Xinjiang province of China, with a reserve of 90 billion tons, is one of the most representative high-chlorine-alkaline coal. However, the chlorine content in coal exceeding 1% easily leads to severe problems of ash deposition and hot corrosion on tubes, which are closely related to the evolution of fine particles. In this study, the formation of fine particle from the combustion of two types of SEH coal (#1 and #2) are investigated in the temperature range of 900–1300 °C. Their results are compared with Xinjiang Tianchi (TC) coal (high-sodium but low-chlorine). In order to demonstrate the formation mechanism of fine particles, the particle size distribution, elemental composition and morphology of fine particles, as well as chlorine- and sulfur-containing gas products, are characterized. The results show that the particle size distribution of PM10 present a bimodal distribution. Fine-mode particles (PM0.4) from SEH#1 coal combustion mainly consist of NaCl since the molar ratio of Na/Cl is about 1.0, while fine-mode particles from TC coal combustion could be Na2SO4 and CaSO4. Coarse-mode particles (PM0.4-10) mainly consist of silicon, aluminum, calcium and magnesium, whose compositions are not significantly affected by combustion temperature, and calcium accounts for the largest proportion in coarse-mode particles. As the temperature increased to 1150 °C, the chlorine and sulfur in SEH coal were fundamentally associated to solid ashes, while for TC coal extra sulfur existed as the gaseous form of SO2.

Concentrations, particle-size distributions, and dry deposition fluxes of aerosol trace elements over the Antarctic Peninsula in austral summer

Abstract. Size-segregated particulate air samples were collected during the austral summer of 2016–2017 at Palmer Station on Anvers Island, western Antarctic Peninsula, to characterize trace elements in aerosols. Trace elements in aerosol samples – including Al, P, Ca, Ti, V, Mn, Ni, Cu, Zn, Ce, and Pb – were determined by total digestion and a sector field inductively coupled plasma mass spectrometer (SF-ICP-MS). The crustal enrichment factors (EFcrust) and k-means clustering results of particle-size distributions show that these elements are derived primarily from three sources: (1) regional crustal emissions, including possible resuspension of soils containing biogenic P, (2) long-range transport, and (3) sea salt. Elements derived from crustal sources (Al, P, Ti, V, Mn, Ce) with EFcrust&lt;10 were dominated by the coarse-mode particles (&gt;1.8 µm) and peaked around 4.4 µm in diameter, reflecting the regional contributions. Non-crustal elements (Ca, Ni, Cu, Zn, Pb) showed EFcrust&gt;10. Aerosol Pb was primarily dominated by fine-mode particles, peaking at 0.14–0.25 µm, and likely was impacted by air masses from southern South America based on air mass back trajectories. However, Ni, Cu, and Zn were not detectable in most size fractions and did not present clear size patterns. Sea-salt elements (Ca, Na+, K+) showed a single-mode distribution and peaked at 2.5–4.4 µm. The estimated dry deposition fluxes of mineral dust for the austral summer, based on the particle-size distributions of Al measured at Palmer Station, ranged from 0.65 to 28 mg m−2 yr−1 with a mean of 5.5±5.0 mg m−2 yr−1. The estimated dry deposition fluxes of the target trace elements in this study were lower than most fluxes reported previously for coastal Antarctica and suggest that atmospheric input of trace elements through dry deposition processes may play a minor role in determining trace element concentrations in surface seawater over the continental shelf of the western Antarctic Peninsula.

Lidar observation of aerosol transformation in the atmospheric boundary layer above the Baltic Sea

Investigation results of a coarse and accumulation mode of aerosol properties above the Baltic Sea are reported. A most important role in the direct aerosol effect on climate have aerosols from the group of coarse and accumulation mode particles. Overseas in the atmosphere, there is a lot of aerosols from the fine fraction but their impact is not so important as coarse and accumulation mode particles. Sea spray emission from the sea surface takes place over a wide range of aerosol particle size distribution, it is also large in size range which are studying in this work (Lewis and Schwartz, 2004). The discussed range is most important in view of atmospheric optical properties, smaller particles do not have such an influence on scattering as particles from range 0.5–2 µm. The research was performed with a multiwavelength lidar. Due to the application of special software, the aerosol particle size distributions were retrieved from the lidar returns. That provided an opportunity to determine the profiles of the aerosol effective radius. We showed that the aerosol properties depend mainly on the direction of the air mass advection and the wind speed. The impact of the Baltic Sea on the aerosol size distribution is huge in the case of the advection from the open sea. Moreover, the aerosol effective radiuses in the whole boundary layer are much larger in the case of strong than for light wind. Our results suggest that the aerosol flux and the aerosol particle size distribution should be related to the wind speed in the emission function.

Analysis of Aerosol Type and Fine- and Coarse-mode Aerosol Direct Radiative Forcing over Regions in East and Southeast Asia Based on AERONET Version 3 Data

ABSTRACT Based on the particle linear depolarization ratio (PLDR) and single-scattering albedo (SSA) values obtained for 1020 nm from Aerosol Robotic Network (AERONET) Version 3 Level 2.0 data collected in five regions, namely, northern China, Northwest Asia, the Tibetan Plateau, southern China and Southeast Asia, we classified seven types of aerosol (viz., purely dust, dust-dominated, pollution-dominated, non-absorbing [NA], weakly absorbing [WA], moderately absorbing [MA] and strongly absorbing [SA]) in order to assess the spatial and temporal distributions of their constituents and the radiative effects of their fine- and coarse-mode particles. The fine fraction dominated in northern China and also played a crucial role on the Tibetan Plateau and in southern China and Southeast Asia, whereas the coarse fraction prevailed in Northwest Asia. Furthermore, the fine-mode aerosol on the Tibetan Plateau exhibited its maximum radiative forcing efficiency (110.3 W m–2) during high concentrations of SA aerosol. Also, the lowest values for both the radiative forcing and the radiative forcing efficiency in southern China occurred during summer. Finally, the various aerosol constituents displayed distinct spatial and temporal distributions in Southeast Asia, with the SA aerosol contributing approximately 20% of the total aerosol on the Indochinese Peninsula and the NA and WA aerosol forming the largest percentages on the Malay Peninsula.

Vertical and spatial distribution of elevated aerosol layers obtained using long-term ground-based and space-borne lidar observations

In this study, long-term ground-based and space-borne lidar measurements are used to understand the vertical (surface to 30 km) and spatial distribution of aerosols. First, the vertical distribution of aerosol extinction (AE) covering from near surface to 30 km is provided by combining Micro Pulse Lidar and Mie lidar observations co-located over a tropical station Gadanki (13.5oN, 79.2oE), India. The presence of two elevated aerosol layers, one between 2 and 5 km (lower troposphere) and the other between 15 and 18 km (Upper Troposphere and Lower Stratosphere (UTLS)), are simultaneously observed during the Indian summer monsoon season. Second, the spatial extent of these elevated aerosol layers obtained using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) measurements reveals the presence of the lower layer extending from Africa to South Asia during both pre–monsoon and monsoon seasons. However, the UTLS layer is confined from middle-east to the China Sea only during monsoon season, also known as Asian Tropopause Aerosol Layer (ATAL). Third, aerosol sub-types obtained for these elevated aerosol layers using CALIPSO measurements reveals the dominance of polluted dust (44.6%) whereas the occurrence frequency of polluted continental, dust and elevated smoke is ~19.6%, 20.7% and 13.1%, respectively, for the lower layer. However, the frequency of volcanic ash and sulfate aerosols is ~50.3% and 49.7%, respectively, for the UTLS layer. Depolarization ratio (color ratio) values varies between 0.21 and 0.34 (>0.6) in the lower layer while the values >0.15 (<0.6) are present in the UTLS layer during monsoon season revealing the influence of non-spherical and coarse mode particles in the lower layer while spherical and fine mode particles in the UTLS region over the site. This information is very much useful in estimating reliable radiative forcing due to these elevated aerosol layers on the background atmosphere involved in assessing their impact on the regional climate.

On the concentration of SARS-CoV-2 in outdoor air and the interaction with pre-existing atmospheric particles

The spread of SARS-CoV-2 by contact (direct or indirect) is widely accepted, but the relative importance of airborne transmission is still controversial. Probability of outdoor airborne transmission depends on several parameters, still rather uncertain: virus-laden aerosol concentrations, viability and lifetime, minimum dose necessary to transmit the disease. In this work, an estimate of outdoor concentrations in northern Italy (region Lombardia) was performed using a simple box model approach, based on an estimate of respiratory emissions, with a specific focus for the cities of Milan and Bergamo (Italy). In addition, the probability of interaction of virus-laden aerosol with pre-existing particles of different sizes was investigated. Results indicate very low (<1 RNA copy/m3) average outdoor concentrations in public area, excluding crowded zones, even in the worst case scenario and assuming a number of infects up to 25% of population. On average, assuming a number of infects equal to 10% of the population, the time necessary to inspire a quantum (i.e. the dose of airborne droplet nuclei required to cause infection in 63% of susceptible persons) would be 31.5 days in Milan (range 2.7–91 days) and 51.2 days in Bergamo (range 4.4–149 days). Therefore, the probability of airborne transmission due to respiratory aerosol is very low in outdoor conditions, even if it could be more relevant for community indoor environments, in which further studies are necessary to investigate the potential risks. We theoretically examined if atmospheric particles can scavenge virus aerosol, through inertial impact, interception, and Brownian diffusion. The probability was very low. In addition, the probability of coagulation of virus-laden aerosol with pre-existing atmospheric particles resulted negligible for accumulation and coarse mode particles, but virus-laden aerosol could act as sink of ultrafine particles (around 0.01 μm in diameter). However, this will not change significantly the dynamics behaviour of the virus particle or its permanence time in atmosphere.

From a polar to a marine environment: has the changing Arctic led to a shift in aerosol light scattering properties?

Abstract. The study of long-term trends in aerosol optical properties is an important task to understand the underlying aerosol processes influencing the change of climate. The Arctic, as the place where climate change manifests most, is an especially sensitive region of the world. Within this work, we use a unique long-term data record of key aerosol optical properties from the Zeppelin Observatory, Svalbard, to ask the question of whether the environmental changes of the last 2 decades in the Arctic are reflected in the observations. We perform a trend analysis of the measured particle light scattering and backscattering coefficients and the derived scattering Ångström exponent and hemispheric backscattering fraction. In contrast to previous studies, the effect of in-cloud scavenging and of potential sampling losses at the site are taken explicitly into account in the trend analysis. The analysis is combined with a back trajectory analysis and satellite-derived sea ice data to support the interpretation of the observed trends. We find that the optical properties of aerosol particles have undergone clear and significant changes in the past 2 decades. The scattering Ångström exponent exhibits statistically significant decreasing of between −4.9 % yr−1 and −6.5 % yr−1 (using wavelengths of λ=450 and 550 nm), while the particle light scattering coefficient exhibits statistically significant increasing trends of between 2.6 % yr−1 and 2.9 % yr−1 (at a wavelength of λ=550 nm). The magnitudes of the trends vary depending on the season. These trends indicate a shift to an aerosol dominated more by coarse-mode particles, most likely the result of increases in the relative amount of sea spray aerosol. We show that changes in air mass circulation patterns, specifically an increase in air masses from the south-west, are responsible for the shift in aerosol optical properties, while the decrease of Arctic sea ice in the last 2 decades only had a marginal influence on the observed trends.

A study on the characteristics of ice nucleating particles concentration and aerosols and their relationship in spring in Beijing

In this study, Bigg cloud chamber was used to determine the concentrations of ice nucleating particles (INPs) in the temperature range from −15 to −30 °C in Beijing in the spring of 2017. The concentrations were compared with historical results observed by a similar instrument in Beijing, showing that the INP concentration in 2017 was generally lower than those obtained in 1995 and 1996. Based on air mass trajectory clustering analysis, the high INP concentration in 1995 and 1996 might be attributable mainly to the transport of sand-dust from the northwestern region. Furthermore, the aerosol number size distribution and chemical composition in PM2.5 were measured simultaneously. The number of aerosols was dominated by particles in Aitken mode and accumulation mode particles during the observation period, but coarse mode particles obviously exhibited stronger correlation with INPs. NO3−, NH4+, and SO42− were the major ions and existed mainly in the form of NH4NO3 and (NH4)2SO4 in PM2.5. Ratio analysis indicated that air pollution originated mainly from mobile sources in Beijing and had serious secondary pollution process. The high ratio of organic carbon (OC) to elemental carbon (EC) implies existing severe secondary organic carbon pollution. In addition, we investigated the relationship between INPs and aerosols with different sizes and compositions in spring in Beijing, the results indicated that for aerosols with a diameter above 0.5 μm, the correlation between INPs and aerosols increased clearly with increasing particle size, but for aerosols with sizes below 0.5 μm, the correlation coefficient displayed a clear trend of increasing first and then decreasing with increasing aerosol size. An INP parameterization depending on aerosol particles and the activation temperature was also established. A comparison of the correlations between the INPs and compositions in PM2.5 shows that NaCl, NH4NO3 and (NH4)2SO4 were more correlated with INPs than other ionic compounds, but a strong correlation existed only at −30 °C, there was no correlation at −20 °C and above. Additionally, OC was more relevant to INP than EC, but the correlation was observed only at low temperature region.

Vertical distributions of the microscopic morphological characteristics and elemental composition of aerosols over India

Particle morphology and elemental compositions are among the crucial parameters of aerosols required for accurate understanding of the climatic effect of aerosols in the earth-atmosphere system; yet their vertical distributions and region specific properties are poorly characterised due to sparse in-situ measurements. This is the first study to classify and quantify the vertical distributions of the morphological characteristics and elemental composition of aerosols based on single particle as well as bulk chemical analysis over seven geographically diverse regions of northern and central parts of India during spring (April–May, 2013), carried out as a part of Regional Aerosol Warming Experiment (RAWEX). Significant regional distinctiveness in shapes (non-sphericity), sizes and elemental compositions of the airborne particles were conspicuous, having dominance of highly irregular granular aggregates over the north Indian sites. The non-spherical coarse mode particles dominated the lower free tropospheric regions (> 2 km) of the Indo-Gangetic Plains (IGP). These particles could be responsible for enhanced spring time aerosol absorption in the elevated region of the atmosphere. Elemental compositions of the single particle analysis indicate that the free tropospheric layer over the IGP and central India is enriched with Na and Ca compounds mixed with Fe or Al (soil particles), indicating long range transport of crustal aerosols. This finding is very well supported by the bulk particle analysis indicating abundance of Ca2+ in the free troposphere with low contribution of ssNa+. Particles with irregular rough surfaces having dominance of SiO2 were observed over all the study sites. The percentage share of spherical (either smooth or rough) particles to the total morphological characteristics of the particles was found to be highly subdued (< 10%). The present study thus critically assesses the relevant knowledge pertaining to the morphological features of aerosols over the IGP during spring for the accurate estimation of aerosol radiative properties. More such efforts are required in future to study the connections and dependencies between morphological and radiative properties of aerosols in different seasons.

Optical properties of atmospheric aerosol over Cape Town, Western Cape of South Africa: Role of biomass burning

The optical characteristics of atmospheric aerosol are vital in the determination of the regional climate trend. Biomass burning is typically known to influence aerosol optical characteristics. Following the incessant biomass burning and the recent drop in precipitation over Western Cape, the aerosol optical properties with a focus on the impact of biomass burning are studied over Cape Town using data from AERONET (Aerosol Robotic Network) and MODIS (Moderate Resolution Imaging Spectroradiometer). In general terms, measurements from both platforms significantly agree on the estimates of aerosol optical depth (AOD) and water vapor content (WVC). The mean AOD 0.075 (± 0.022) and Ångström exponent (AE) 0.63 (± 0.19) derived from AERONET demonstrate the dominance of coarse mode aerosol typical of maritime aerosol. Similarly, aerosol particle size distributions display the predominance of coarse mode particles. However, the derived refractive index is more representative of urban-industrial aerosol. Also, estimated back-trajectories show that more than 70% of the aerosol particles over the region originate over the ocean. Atmospheric vapor increases from winter to summer and mainly influenced by air temperature, supersaturation level, and absorbing aerosol. Furthermore, two significant sources accounted for biomass burning related to high AOD values: local biomass burning and regionally transported aged smoke majorly from elsewhere in Sothern Africa.