Aerosol Number Density Research Articles

Stratospheric aerosol characteristics from SCIAMACHY limb observations: two-parameter retrieval

Abstract. Stratospheric aerosols play a key role in atmospheric chemistry and climate. Their particle size is a crucial factor controlling the microphysical, radiative, and chemical aerosol processes in the stratosphere. Despite its importance, available observations on aerosol particle size are rather sparse. This limits our understanding and knowledge about the mechanisms and importance of chemical and climate aerosol feedbacks. The retrieval described by Malinina et al. (2018) provides the stratospheric particle size distribution (PSD) from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) limb observations in the tropics. This algorithm has now been improved and extended to work on the entire globe. Two PSD parameters of a unimodal lognormal PSD, the median radius and the geometric standard deviation, are retrieved between 18 and 35 km altitude from SCIAMACHY limb observations by a multiwavelength nonlinear regularized inversion. The approach assumes an aerosol particle number density profile that does not change during the retrieval. The effective Lambertian surface albedo pre-retrieved from coinciding SCIAMACHY nadir observations is integrated into the retrieval algorithm to mitigate the influence of the surface albedo on the retrieval results. The extinction coefficient and the effective radius are calculated from the PSD parameters. The aerosol characteristics from SCIAMACHY are compared with in situ balloon-borne measurements from Laramie, Wyoming, and retrievals from the satellite instruments of the Stratospheric Aerosol and Gas Experiment series (SAGE II and SAGE III) and Optical Spectrograph and InfraRed Imager System (OSIRIS). In the Northern Hemisphere, the median radius differs by less than 27 % and the geometric standard deviation by less than 11 % from both balloon-borne and SAGE III data. Differences are mainly attributed to errors in the assumed a priori number density profile. Globally, the SCIAMACHY extinction coefficient at 750 nm deviates by less than 35 % from SAGE II, SAGE III, and OSIRIS data. The effective radii from SCIAMACHY, balloon-borne measurements, and SAGE III agree within about 18 %, while the effective radius based on SAGE II measurements is systematically larger. The novel data set containing the PSD parameters, the effective radius, and the aerosol extinction coefficients at 525, 750, and 1020 nm from SCIAMACHY observations is publicly available.

Impact of Planetary Parameters on Water Clouds Microphysics

Potentially habitable exoplanets are targets of great interest for the James Webb Space Telescope and upcoming mission concepts such as the Habitable Worlds Observatory. Clouds strongly affect climate and habitability, but predicting their properties is difficult. In Global Climate Models (GCMs), especially those aiming at simulating Earth, cloud microphysics is often crudely approximated by assuming that all cloud particles have a single, constant size or a prescribed size distribution and that all clouds in a grid cell are identical. For exoplanets that range over a large phase space of planetary properties, this method could result in large errors. In this work, our goal is to determine how cloud microphysics on terrestrial exoplanets, whose condensable is mainly water vapor, depend on aerosol properties and planetary parameters such as surface pressure, surface gravity, and incident stellar radiation. We use the Community Aerosol and Radiation Model for Atmospheres as a 1D microphysical model to simulate the formation and evolution of clouds including the processes of nucleation, condensation, evaporation, coagulation, and vertical transfer. In these 1D idealized experiments, we find that the parameters that determine the macrophysical thermal structure of the atmospheres, including surface pressure and stellar flux, impact cloud radiative effect (CRE) most significantly. Parameters such as gravity and number density of aerosols working as cloud condensation nuclei affect the microphysical processes of cloud formation, including activation and vertical transfer. They also have a significant, though weaker effect on CRE. This work motivates the development of more accurate GCM cloud schemes and should aid in the interpretation of future observations.

Dew, frost, fog and lifted temperature minima: Observations in southern England and implications for modelling

AbstractGiven difficulties with modelling radiation fog and the similarity of meteorological conditions linked to dewfall and frost we investigated the formation of dew, frost and fog. For a site in the UK seven years of data were analysed representing high‐resolution atmospheric profiles and dew meter measurements for radiation nights with stable conditions. Classical dewfall occurs by condensation when the surface is below the dew point and cooler than the air above. However, the profiles show that, in the absence of fog, typically dew and frost form with the surface warmer than the immediately overlying air due to lifted temperature minima (LTMs) at about 0.15 m. Observations of aerosol number density and average hydrated radii show that aerosol optical extinction (and hence their radiative effect) is weakly but significantly correlated with the intensity of LTMs. Low wind speed on stable nights allows settling of aerosols which radiatively cool the air near the ground more quickly than the surface cools – thus creating LTMs. In the presence of LTMs typically dew and frost form not by condensation, but by occult deposition of water droplets onto the canopy and ground. Among radiation fog observations, 91% are associated with light near‐surface winds and LTMs. When the rate of removal of suspended water droplets by occult deposition generating dew or frost is too slow, then build‐up of droplets in the air just above the surface leads to the formation of radiation fog. Future modelling should allow for the accumulation of near‐surface aerosols and their radiative effects during stable nights to represent the formation of LTMs. Modelling of typical dew and frost will require representation of occult deposition. Assessing rates of occult deposition compared to rates of generation of suspended water droplets is needed to forecast the onset of radiation fog formed near the ground.

Distribution of atmospheric aerosols during the 2007 Mars dust storm (MY 28): Solar infrared occultation observations by SPICAM

Solar occultation measurements by the SPICAM IR on Mars-Express have been used to study aerosol vertical distribution during the 2007 global dust storm (GDS) of Mars Year 28. Measurements in the near-IR spectral range from 1 to 1.7 μm provide information about aerosol optical properties, extinction coefficient, particle size and number density. The observations were performed at Ls = 254–302° of MY28 and latitudes from 65°S to 65°N. Within the SPICAM spectral range we could not distinguish between absorption due to dust or water ice. The particle size distribution and its parameters, the effective radius reff and variance νeff, are retrieved assuming either mineral dust or water ice refraction indices. Before the MY 28 GDS at Ls < 265° the aerosol was detected from 20 to 60 km with dust particle size ∼0.75 μm below 50 km and decreasing with altitude above. The detached layers, presumably consisting of water ice, were observed at ∼60 km in the Southern hemisphere and 45 km in the Northern and Southern hemispheres with opacity <0.02 and 0.01–0.15, respectively. The effective radius varied from 0.2 to 1.6 μm with number density from 0.4 to 50 cm−3. With the development of the GDS dust reached to 80 km and higher, while reff tended to increase with altitude up to 0.9–1 μm at 70–75 km. The dust number density decreased from 2 to 4 cm−3 at 40 km to 0.1 cm−3 at 70–80 km. The dependence of the effective variance on altitude and season has been studied. Before the beginning GDS νeff varied below 50–60 km from 0.2 to 0.4 in the Southern hemisphere to 0.4–0.6 in the Northern hemisphere. During the GDS, the wider distribution propagated higher, with νeff ∼ 0.5 up to 70 km in the southern hemisphere. In high latitudes of both hemispheres at Ls = 268–275° optically thin water ice high altitude clouds were detected at 80–90 km with reff < 0.5 μm and number density 10–100 cm−3.

In situ measurements of perturbations to stratospheric aerosol and modeled ozone and radiative impacts following the 2021 La Soufrière eruption

Abstract. Stratospheric aerosols play important roles in Earth's radiative budget and in heterogeneous chemistry. Volcanic eruptions modulate the stratospheric aerosol layer by injecting particles and particle precursors like sulfur dioxide (SO2) into the stratosphere. Beginning on 9 April 2021, La Soufrière erupted, injecting SO2 into the tropical upper troposphere and lower stratosphere, yielding a peak SO2 loading of 0.3–0.4 Tg. The resulting volcanic aerosol plumes dispersed predominately over the Northern Hemisphere (NH), as indicated by the CALIOP/CALIPSO satellite observations and model simulations. From June to August 2021 and May to July 2022, the NASA ER-2 high-altitude aircraft extensively sampled the stratospheric aerosol layer over the continental United States during the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) mission. These in situ aerosol measurements provide detailed insights into the number concentration, size distribution, and spatiotemporal variations of particles within volcanic plumes. Notably, aerosol surface area density and number density in 2021 were enhanced by a factor of 2–4 between 380–500 K potential temperature compared to the 2022 DCOTSS observations, which were minimally influenced by volcanic activity. Within the volcanic plume, the observed aerosol number density exhibited significant meridional and zonal variations, while the mode and shape of aerosol size distributions did not vary. The La Soufrière eruption led to an increase in the number concentration of small particles (&lt;400 nm), resulting in a smaller aerosol effective diameter during the summer of 2021 compared to the baseline conditions in the summer of 2022, as observed in regular ER-2 profiles over Salina, Kansas. A similar reduction in aerosol effective diameter was not observed in ER-2 profiles over Palmdale, California, possibly due to the values that were already smaller in that region during the limited sampling period in 2022. Additionally, we modeled the eruption with the SOCOL-AERv2 aerosol–chemistry–climate model. The modeled aerosol enhancement aligned well with DCOTSS observations, although the direct comparison was complicated by issues related to the model's background aerosol burden. This study indicates that the La Soufrière eruption contributed approximately 0.6 % to Arctic and Antarctic ozone column depletion in both 2021 and 2022, which is well within the range of natural variability. The modeled top-of-atmosphere 1-year global average radiative forcing was −0.08 W m−2 clear-sky and −0.04 W m−2 all-sky. The radiative effects were concentrated in the tropics and NH midlatitudes and diminished to near-baseline levels after 1 year.

Baseline Balloon Stratospheric Aerosol Profiles (B2SAP)—Systematic Measurements of Aerosol Number Density and Size

AbstractStratospheric aerosol plays an important role in Earth's radiative balance. Systematic measurements of stratospheric aerosol number concentration and size are needed to characterize their baseline values and variability, improve understanding of aerosol microphysics, and assess the representation of stratospheric aerosol processes in global models. In situ measurements of particle size distribution provide insight into the responses of stratospheric aerosol processes to perturbations from volcanoes and wildfires, anthropogenic emissions from rockets and aircraft, or intentional injections related to climate intervention. The Baseline Balloon Stratospheric Aerosol Profiles (B2SAP) project uses compact, lightweight payloads carried by meteorological balloons to measure aerosol number density and size distributions, water vapor, ozone, and meteorological data from the surface to the middle stratosphere. The long‐term goal for the B2SAP project is to produce climatologies of aerosol number and size distributions into the middle stratosphere at latitudinally distributed measurement sites. Since March 2019, B2SAP payloads have been launched from Boulder, CO, USA once to twice per month and four to six times per year from Lauder, NZ. These measurements provide a new record of in situ stratospheric aerosol observations and are being used to help validate satellite‐based estimates of stratospheric aerosol size distributions. Here we present 50 vertical profiles from Boulder, CO, from March 2019 to March 2022, to build a NH mid‐latitude climatology of stratospheric aerosol and its variability and investigate the impact of natural perturbations on stratospheric aerosol microphysics.

The Low‐Altitude Ionosphere of the Ice Giant Planets

AbstractThe study of atmospheric electricity of the lower stratosphere and upper troposphere of the ice giant planets can help to understand several physical phenomena such as cloud formation, lightning generation, aerosols growth, or chemical composition. At these depths, galactic radiation is the main energy source able to ionize the atmospheric constituents and to produce a low altitude ionospheric layer that can be similar in magnitude to the upper ionosphere produced by solar radiation and auroral electrons. The presence of aerosols affects the ion‐neutral chemistry by capturing electrons and ions depending on the aerosol size and number density. Here, we present a new one dimensional ionospheric model of Uranus and Neptune able to calculate the number densities of electrons and ions as well as the charging of aerosols between 100 Pa and 4 × 105 Pa. Since the results depends upon the amount and size of the atmospheric aerosols, as well as on the flux of the incoming cosmic radiation, several aerosol models, solar‐cycle conditions, and the effect of the intrinsic magnetic field are considered.

Three-dimensional modeling of Venus photochemistry and clouds

We present here three-dimensional simulations of the Venus photochemistry and clouds from the ground to the bottom of the thermosphere. For that purpose, we have implemented a state-of-the-art photochemical and equilibrium cloud model in the Venus Planetary Climate Model (Venus PCM). The interactive coupling between dynamics, radiation, chemistry and clouds allows a comprehensive description of the CO2, CO, sulfur, chlorine, oxygen, and hydrogen species, with tracking of the condensed phase. Regarding the clouds, the Venus PCM calculates the composition, number density, and sedimentation rates of the binary H2SO4-H2O liquid aerosols, based on observed altitude-dependent size distributions. The article describes in detail the new components implemented in the Venus PCM. It then presents an overview of the results concerning clouds and atmospheric chemistry, which are compared with a wide range of observations. The modeled cloud characteristics and vertical profiles of minor species are found to be in broad agreement with most of the measurements available between 30 and 100 km. In particular, the Venus PCM reproduces the steep decrease of H2O and SO2 mixing ratio inside the cloud layer, as well as the observed vertical distribution of species well identified above the clouds, such as CO and O3. The model also agrees with the ground-based measurements of HCl, but not with the conflicting HCl vertical profiles derived from Venus Express. On the quasi-horizontal plane, latitudinal contrasts in the modeled trace species mostly result from the Hadley-type mean meridional circulation. Large-scale longitudinal variations are essentially created by the diurnal thermal tide above the clouds, and by photolysis above 80 km.

Aerosol impacts on fog microphysics over the western side of Taiwan Strait in April from 2015 to 2017

Fog has drawn much attention from scholars and the public; it can reduce visibility to less than 1 km and affect air, sea, and land transportation and economy. In late winter and spring, fog events frequently affect intensive human activity in the coastal areas of Eastern China. In this study, numerical simulations from the Weather Research and Forecasting model were combined with observations to investigate the effects of aerosol on the microphysical properties of fog over the Taiwan Strait in April from 2015 to 2017. The mean values of observed liquid water content, number concentration of fog droplets, and mean diameter fog droplets were 0.11 g/m3, 2.2 × 108 #/m3, and 13.9 μm. The observed relationships between fog microphysical properties were close to the simulation results in the urban aerosol experiment, suggesting that the fog events at Kinmen were significantly affected by urban aerosols. The simulation results indicated that the wind blew from the south, and the air temperature was about 1°C higher than the sea surface temperature on foggy days. A stable condition accompanied by a shallow planetary boundary layer was favorable to fog formation. In the urban aerosol experiment, higher number density of aerosols resulted in more but smaller droplets and increased the LWC. An increase in aerosols reflected shortwave radiation, resulting in a colder and wetter atmosphere during fog events in the daytime. This led to a thicker fog layer and an increased number of fog droplets in the urban aerosol experiment. Foggy days and microphysical properties at Kinmen significantly differed between the studied years. As suggested by the correlations between fog-day anomalies and the corresponding Niño 3.4 index and Oceanic Niño Index, this interannual difference might be attributable to the 2015 to 2016 El Niño–Southern Oscillation (ENSO). Further observations are required to ascertain the relationship between fog events, fog microphysics, and ENSO events.

Study of aerosol vertical distribution during meteor showers of January 2009

Atmospheric aerosols are minute particles (1 nm–100 μm) suspended in various layers of the Earth's atmosphere. During meteor showers, huge amount of cosmic debris called meteoroids enters into the Earth's atmosphere. These particles contribute to aerosols in the mesosphere and lower thermosphere. The aerosols emerged from meteor dust particles are having different size. The displacement of the particles through the atmosphere is directly proportional to their size. Therefore, we observed several maxima on the post-shower aerosol vertical profiles. One attempt is made to study correlation between the mesospheric and lower thermospheric Aerosol Number Density per cm3 (AND) and different types of Meteor Showers i.e. strong, medium-level and weak. Another attempt is made to trace the journey of meteor matter through lower atmospheric layers. The changes in AND are studied under this topic by using the data collected during January 2009 at Kolhapur (16°39′42.2″N, 74°14′20.8″E) by using Semiautomatic Twilight Photometer. This instrument provides the qualitative picture of vertical distribution of atmospheric aerosols from about 6 km to 360 km with the height resolution of 30 m at tropospheric levels.

Radiative characteristics of near-surface aerosols at a tropical site: An estimation based on concurrent measurements of their physico-chemical characteristics

This study is an attempt to estimate the radiative characteristics of aerosols, namely, the scattering coefficient (βsc), absorption coefficient (βab), extinction coefficient (βex), single scattering albedo (ω) and the phase function P(θ), on a seasonal basis, incorporating the concurrent measurements of aerosol mass loading, size distribution and chemical composition at the tropical coastal site, Thiruvananthapuram. The software package Optical Properties of Aerosols and Clouds (OPAC) has been made use for the estimation of the radiative parameters. This paper presents the seasonal features of aerosol chemical composition and their source characteristics also. Along with this, the association between size-resolved number density of aerosols and their chemical characteristics were also investigated through correlation analysis. The location is significantly influenced by human activities as seen from the dominance of the anthropogenic component which is highest in winter (22%) with comparable values in pre-monsoon and post-monsoon and minimum in monsoon (13%). The sea-salt contribution is found to peak in monsoon (~40%) and attain a minimum in winter. The source characterization using principal component analysis along with back-trajectory analysis showed the seasonally changing mixed aerosol sources over the region. Accordingly, the radiative properties of aerosols also exhibit significant seasonal variations. βsc varied from 0.04 to 0.14 km−1 and βab between 0.01 and 0.05 km−1 over a year. The single-scattering albedo exhibited significant seasonal differences being ~0.71 for winter and ~0.89 (0.55 μm) for monsoon season, indicating the presence of more absorbing aerosols in winter.

Aerosol variations in the upper troposphere and lower stratosphere over the Tibetan Plateau

Satellite measurements and model simulations indicate the existence of the Asian tropopause aerosol layer (ATAL)—an enhanced aerosol layer in the upper troposphere and lower stratosphere (UTLS) associated with the Asian summer monsoon (ASM)—although it has rarely been evidenced by snapshots of balloon-borne in situ measurements. To better understand how the ATAL evolves, a portable optical particle counter (POPS) onboard a stratospheric balloon was released over the Tibetan Plateau (TP) during the ASM period of 2019. The POPS detected the ATAL in the UTLS during the ascending, descending periods, as well as during its quasi-horizontal floating periods. The aerosol number density in the ATAL showed obvious vertical variability. The peak aerosol number density in the ATAL was 180 cm−3 around the tropopause during the ascending and descending period and the maximum aerosol number density was 290 cm−3 around the tropopause during the floating period. And the aerosol concentration observed over the TP in the 2019 summer was approximately five times larger than that in the 2018 summer. Lagrangian simulations reveal that the minority of the observed aerosol particles were directly elevated in a region of uplift south of the Himalayas, and the majority of the particles were transported from the UTLS region situated approximately between the isentropic surfaces of 370 and 460 K. Up to 14% of the observed aerosol particles were directly influenced by the volcanic plumes from the eruption of the volcano Raikoke in June 2019.

Homogeneous nucleation of carbon dioxide in supersonic nozzles I: experiments and classical theories.

We studied the homogeneous nucleation of carbon dioxide in the carrier gas argon for concentrations of CO2 ranging from 2 to 39 mole percent using three experimental methods. Position-resolved pressure trace measurements (PTM) determined that the onset of nucleation occurred at temperatures between 75 and 92 K with corresponding CO2 partial pressures of 39 to 793 Pa. Small angle X-ray scattering (SAXS) measurements provided particle size distributions and aerosol number densities. Number densities of approximately 1012 cm-3, and characteristic times ranging from 6 to 13 μs, resulted in measured nucleation rates on the order of 5 × 1017 cm-3 s-1, values that are consistent with other nucleation rate measurements in supersonic nozzles. Finally, we used Fourier transform infrared (FTIR) spectroscopy to identify that the condensed CO2 particles were crystalline cubic solids with either sharp or rounded corners. Molecular dynamics simulations, however, suggest that CO2 forms liquid-like critical clusters before transitioning to the solid phase. Furthermore, the critical clusters are not in thermal equilibrium with the carrier gas. Comparisons with nucleation theories were therefore made assuming liquid-like critical clusters and incorporating non-isothermal correction factors.

In situ measurements and backward-trajectory analysis of high-concentration, fine-mode aerosols in the UTLS over the Tibetan Plateau

An aerosol layer in the upper troposphere and lower stratosphere over the Asian summer monsoon (ASM) regions, namely, the Asian tropopause aerosol layer (ATAL), has been observed based on satellite remote sensing and in situ measurements; however, its source is still under debate. In August 2018, an experimental campaign over the Tibetan Plateau at Golmud (GLM, 36.48 °N, 94.93 °E) was performed, during which a balloon-borne Portable Optical Particle Counter was used to measure the aerosol particle profile. Backward-trajectory simulations were conducted with the Massive-Parallel Trajectory Calculations model to investigate the possible sources and transport pathways of the observed particles. The in situ measurements showed a robust ATAL around the tropopause, 16 km above sea level, with a maximum aerosol number density of 35 cm−3 and a maximum aerosol mass concentration of 0.15 μg m−3 for particles with diameters between 0.14 and 3 μm. The aerosol particles in the ATAL are mostly smaller than 0.25 μm in diameter, accounting for 98% of all aerosol particles detected. The backward-trajectory analysis revealed that the air parcels arrived at the altitude of the ATAL through two separate pathways: (1) the uplift below the 360 K isentropic surface, where air parcels were first elevated to the upper troposphere and then joined the ASM anticyclonic circulation; and (2) the quasi-horizontal transport along the anticyclonic circulation, located approximately between the 360 and 420 K isentropic surfaces. The complex transport pathways may aggravate the challenge of analyzing the composition of the ATAL, and further observation campaigns are required to extend our knowledge.

Sea salt aerosol production via sublimating wind-blown saline snow particles over sea ice: parameterizations and relevant microphysical mechanisms

Abstract. Blowing snow over sea ice has been proposed as a significant source of sea salt aerosol (SSA) (Yang et al., 2008). In this study, using snow salinity data and blowing snow and aerosol particle measurements collected in the Weddell Sea sea ice zone (SIZ) during a winter cruise, we perform a comprehensive model–data comparison with the aim of validating proposed parameterizations. Additionally, we investigate possible physical mechanisms involved in SSA production from blowing snow. A global chemical transport model, p-TOMCAT, is used to examine the model sensitivity to key parameters involved, namely blowing-snow size distribution, snow salinity, sublimation function, surface wind speed, relative humidity, air temperature and ratio of SSA formed per snow particle. As proposed in the parameterizations of Yang et al. (2008), the SSA mass flux is proportional to the bulk sublimation flux of blowing snow and snow salinity. To convert the bulk sublimation flux to SSA size distribution requires (1) sublimation function for snow particles, (2) blowing-snow size distribution, (3) snow salinity and (4) ratio of SSA formed per snow particle. The optimum model–cruise aerosol data agreement (in diameter range of 0.4–12 µm) indicates two possible microphysical processes that could be associated with SSA production from blowing snow. The first one assumes that one SSA is formed per snow particle after sublimation, and snow particle sublimation is controlled by the curvature effect or the so-called “air ventilation” effect. The second mechanism allows multiple SSAs to form per snow particle and assumes snow particle sublimation is controlled by the moisture gradient between the surface of the particle and the ambient air (moisture diffusion effect). With this latter mechanism the model reproduces the observations assuming that one snow particle produces ∼10 SSA during the sublimation process. Although both mechanisms generate very consistent results with respect to observed aerosol number densities, they correspond to completely different microphysical processes and show quite different SSA size spectra, mainly in ultra-fine and coarse size modes. However, due to the lack of relevant data, we could not, so far, conclude confidently which one is more realistic, highlighting the necessity of further investigation.

Construction and Characterization of an Indoor Smog Chamber for Measuring the Optical and Physicochemical Properties of Aging Biomass Burning Aerosols

ABSTRACT We describe here the construction and characterization of a new combustion-chamber system (the NCAT chamber) for studying the optical and physicochemical properties of biomass burning (BB) aerosols. This system is composed of a ~9 m3 fluorinated ethylene propylene (FEP) film reactor placed in a temperature-controlled room that uses a tube furnace to combust biomass fuel samples under controlled conditions. The optical properties are measured using a cavity ring-down spectrometer and nephelometer. Aerosol number density and size classification used condensation particle counter, and differential mobility analyzer. Other analytical instruments, used include NOx, O3, CO, and CO2 analyzers, a gas chromatograph, and particle filter samples for determining the physicochemical and morphological properties. The construction details and characterization experiments are described, including measurements of the BB particulate size distribution and deposition rate, gas wall loss rates, dilution rate, light intensity, mixing speed, temperature and humidity variations, and air purification method. The wall loss rates for NO, NO2, and O3 were found to be (7.40 ± 0.01) × 10–4, (3.47 ± 0.01) × 10–4, and (5.90 ± 0.08) × 10–4 min–1, respectively. The NO2 photolysis rate constant was 0.165 ± 0.005 min–1, which corresponds to a flux of (7.72 ± 0.25) × 1017 photons nm cm–2 s–1 for 296.0–516.8 nm, and the particle deposition rate was (9.46 ± 0.18) × 10–3 min–1 for 100 nm mobility diameter BB particles from pine. Preliminary results of the single scattering albedo of fresh and aged BB aerosols are also reported.

Physicochemical studies of aerosols at Montreal Trudeau Airport: The importance of airborne nanoparticles containing metal contaminants

Airborne particles, specifically nanoparticles, are identified health hazards and a key research domain in air pollution and climate change. We performed a systematic airport study to characterize real-time size and number density distribution, chemical composition and morphology of the aerosols (∼10 nm–10 μm) using complementary cutting-edge and novel techniques, namely optical aerosol analyzers, triple quad ICP-MS/MS and high-resolution STEM imaging. The total number density of aerosols, predominantly composed of nanoparticles, reached a maximum of 2 × 106 cm−3 and is higher than reported values from any other international airport. We also provide evidence for a wide range of metal in aerosols, and emerging metals in nanoparticles (e.g., Zn and Ni). The geometric mean, median and 99th and 1st percentile values of observed nanoparticle number densities at the apron were 1.0 × 105, 9.0 × 104, 1.2 × 106 and 9.3 × 103 cm−3, respectively. These observations were statistically higher than corresponding measurements in downtown Montreal and at major highways during rush hour. This airport is thus a hotspot for nanoparticles containing emerging contaminants. The diurnal trends in concentrations exhibit peaks during flight and rush hours, showing correlations with pollutants such as CO. The HR-TEM-EDS provided evidence for nano-sized particles produced in combustion engines. Implications of our results for air pollution and health are discussed.

Aerosol particle size distribution in the stratosphere retrieved from SCIAMACHY limb measurements

Abstract. Information about aerosols in the Earth's atmosphere is of a great importance in the scientific community. While tropospheric aerosol influences the radiative balance of the troposphere and affects human health, stratospheric aerosol plays an important role in atmospheric chemistry and climate change. In particular, information about the amount and distribution of stratospheric aerosols is required to initialize climate models, as well as validate aerosol microphysics models and investigate geoengineering. In addition, good knowledge of stratospheric aerosol loading is needed to increase the retrieval accuracy of key trace gases (e.g. ozone or water vapour) when interpreting remote sensing measurements of the scattered solar light. The most commonly used characteristics to describe stratospheric aerosols are the aerosol extinction coefficient and Ångström coefficient. However, the use of particle size distribution parameters along with the aerosol number density is a more optimal approach. In this paper we present a new retrieval algorithm to obtain the particle size distribution of stratospheric aerosol from space-borne observations of the scattered solar light in the limb-viewing geometry. While the mode radius and width of the aerosol particle size distribution are retrieved, the aerosol particle number density profile remains unchanged. The latter is justified by a lower sensitivity of the limb-scattering measurements to changes in this parameter. To our knowledge this is the first data set providing two parameters of the particle size distribution of stratospheric aerosol from space-borne measurements of scattered solar light. Typically, the mode radius and w can be retrieved with an uncertainty of less than 20 %. The algorithm was successfully applied to the tropical region (20° N–20° S) for 10 years (2002–2012) of SCIAMACHY observations in limb-viewing geometry, establishing a unique data set. Analysis of this new climatology for the particle size distribution parameters showed clear increases in the mode radius after the tropical volcanic eruptions, whereas no distinct behaviour of the absolute distribution width could be identified. A tape recorder, which describes the time lag as the perturbation propagates to higher altitudes, was identified for both parameters after the volcanic eruptions. A quasi-biannual oscillation (QBO) pattern at upper altitudes (28–32 km) is prominent in the anomalies of the analysed parameters. A comparison of the aerosol effective radii derived from SCIAMACHY and SAGE II data was performed. The average difference is found to be around 30 % at the lower altitudes, decreasing with increasing height to almost zero around 30 km. The data sample available for the comparison is, however, relatively small.

Season-dependent size distribution of aerosols over the tropical coastal environment of south-west India

This paper presents the results of a detailed study on the size characteristics of aerosols at the tropical coastal site Thiruvananthapuram based on the in-situ measurements of size resolved aerosol number density using an aerosol spectrometer, covering a period of 28 months from September 2011 to December 2013. The diurnal pattern of aerosol number density is characterized by day time low and a two-fold increase during nighttime and these changes are closely associated with the strong mesoscale features namely the sea breeze and land breeze prevailing at the site. Aerosol Number Size Distribution (NSD) depicts a multi-modal nature with two prominent modes, one ≤0.1 μm and other ∼1 μm. Two other less pronounced modes are also observed in the NSD, one ∼0.3–0.5 μm and other ∼5–8 μm. The NSDs also exhibited strong seasonal changes linked with the synoptic meteorological feature of this region namely the South Asian monsoon. The seasonal NSDs were parameterized and analyzed. In addition to this, the effects of meteorological parameters temperature, relative humidity, and wind speed and airflow patterns on aerosol number density as revealed by partial correlation analysis were found to be aerosol size dependent.

Estimation of acoustic forces on submicron aerosol particles in a standing wave field

ABSTRACTThe net acoustic force acting on submicron particles suspended in a gas and exposed to a standing wave field is investigated as a function of particle size, by measuring both the aerosol number density and size distribution in a flow-through resonator. By taking into account all contributions relevant to the net force, this experimental study provides a first estimate for the acoustic radiation force in a size range where molecular effects are expected to be significant. The experiment consists of an electrostatic transducer generating a standing wave in the 50–80 kHz frequency range, with the submicron aerosol particles concentrated at pressure antinodes located across the height of a rectangular channel. A section of the flow is sampled isokinetically and analyzed using a Scanning Mobility Particle Sizer (SMPS), while the nodal patterns are visualized simultaneously using light scattering. The net acoustic force is calculated from their measured displacement along the axis of the 1D standing wav...