Aerosol Microphysical Parameters Research Articles

Multifrequency lidar sounding of air pollution by particulate matter with separation into respirable fractions

A technique is considered for retrieving the spatial distributions of respirable fractions of aerosol in the lower atmosphere on the basis of multifrequency lidar sounding data without the use of additional aerosol optical and microphysical parameters along a sounding path. For this purpose, it is suggested to replace the spectral values of the aerosol extinction coefficient involved in lidar equations with the linearly independent parameters of their approximation, and retrieve the spatial distributions of these parameters from the numerical solution of the set of equations composed of all wavelength-time lidar signal samples. As a result, the number of unknowns in the set of equations to be solved is significantly reduced, and its matrix becomes overdetermined, which can be used for selection of physically reasonable values of the aerosol backscattering phase function at the lidar operating wavelengths. An assumption that there are two segments at the sounding path with similar aerosol extinction coefficient profiles is used to determine the lidar calibration constants. An algorithm is suggested for the search for these segments by the wavelength-time structure of a lidar signal. The inverse problem of aerosol light scattering is solved on the basis of stable regression relations between the concentrations of respirable aerosol fractions and approximation parameters of the aerosol extinction spectrum. The stability of the technique developed to the calibration errors and spatial variations in the aerosol backscattering phase function is shown in numerical experiments on laser sounding of aerosol.

Gradient Correlation Method for the Stabilization of Inversion Results of Aerosol Microphysical Properties Retrieved from Profiles of Optical Data

Correlation relationships between aerosol microphysical parameters and optical data are investigated. The results show that surface-area concentrations and extinction coefficients are linearly correlated with a correlation coefficient above 0.99 for arbitrary particle size distribution . The correlation relationships that we obtained can be used as constraints in our inversion of optical lidar data. Simulation studies demonstrate a significant stabilization of aerosol microphysical data products if we apply the gradient correlation method in our traditional regularization technique.

Technique for determining mass concentrations of aerosol fractions in the surface air from multifrequency lidar sounding data

A technique for determining mass concentrations of aerosol particles smaller than 1.0, 2.5, 10, and 30 µm in the surface air is suggested. The technique involves remote lidar sounding of the atmosphere at the wavelengths λ = 0.355, 0.532, 1.064, 2.13 µm, retrieval of the spectral and spatial distributions of the aerosol extinction coefficient from the lidar signals, and their conversion to the spatial distributions of the concentrations of aerosol fractions on the basis of regression relations between optical and microphysical aerosol parameters. To improve the accuracy and stability of the solution of a system of lidar equations, the calibration constants and lidar ratios at the wavelengths of the sounding radiation are chosen taking into account the multicollinearity of the spectral aerosol extinction coefficients, which is expressed in the form of a multiple regression equation. The regressions were derived within the World Meteorological Organization’s optical model of urban aerosol under wide variations in model parameters which characterize the particle size distribution and the complex refractive index of the aerosol matter. Numerical experiments on remote laser sounding of the mass concentration of aerosol fractions in the atmosphere have shown the robustness of the technique proposed.

High temporal resolution estimates of columnar aerosol microphysical parameters from spectrum of aerosol optical depth by linear estimation: application to long-term AERONET and star-photometry measurements

Abstract. This work deals with the applicability of the linear estimation technique (LE) to invert spectral measurements of aerosol optical depth (AOD) provided by AERONET CIMEL sun photometers. The inversion of particle properties using only direct-sun AODs allows the evaluation of parameters such as effective radius (reff) and columnar volume aerosol content (V) with significantly better temporal resolution than the operational AERONET algorithm which requires both direct sun and sky radiance measurements. Sensitivity studies performed demonstrate that the constraints on the range of the inversion are very important to minimize the uncertainties, and therefore estimates of reff can be obtained with uncertainties less than 30 % and of V with uncertainties below 40 %. The LE technique is applied to data acquired at five AERONET sites influenced by different aerosol types and the retrievals are compared with the results of the operational AERONET code. Good agreement between the two techniques is obtained when the fine mode predominates, while for coarse mode cases the LE results systematically underestimate both reff and V. The highest differences are found for cases where no mode predominates. To minimize these biases, correction functions are developed using the multi-year database of observations at selected sites, where the AERONET retrieval is used as the reference. The derived corrections are tested using data from 18 other AERONET stations offering a range of aerosol types. After correction, the LE retrievals provide better agreement with AERONET for all the sites considered. Finally, the LE approach developed here is applied to AERONET and star-photometry measurements in the city of Granada (Spain) to obtain day-to-night time evolution of columnar aerosol microphysical properties.

Retrieval of aerosol microphysical properties from AERONET photopolarimetric measurements: 1. Information content analysis

AbstractThis paper is the first part of a two‐part study that aims to retrieve aerosol particle size distribution (PSD) and refractive index from the multispectral and multiangular polarimetric measurements taken by the new‐generation Sun photometer as part of the Aerosol Robotic Network (AERONET). It provides theoretical analysis and guidance to the companion study in which we have developed an inversion algorithm for retrieving 22 aerosol microphysical parameters associated with a bimodal PSD function from real AERONET measurements. Our theoretical analysis starts with generating the synthetic measurements at four spectral bands (440, 675, 870, and 1020 nm) with a Unified Linearized Vector Radiative Transfer Model for various types of spherical aerosol particles. Subsequently, the quantitative information content for retrieving aerosol parameters is investigated in four observation scenarios, i.e., I1, I2, P1, and P2. Measurements in the scenario (I1) comprise the solar direct radiances and almucantar radiances that are used in the current AERONET operational inversion algorithm. The other three scenarios include different additional measurements: (I2) the solar principal plane radiances, (P1) the solar principal plane radiances and polarization, and (P2) the solar almucantar polarization. Results indicate that adding polarization measurements can increase the degree of freedom for signal by 2–5 in the scenario P1, while not as much of an increase is found in the scenarios I2 and P2. Correspondingly, smallest retrieval errors are found in the scenario P1: 2.3% (2.9%) for the fine‐mode (coarse‐mode) aerosol volume concentration, 1.3% (3.5%) for the effective radius, 7.2% (12%) for the effective variance, 0.005 (0.035) for the real‐part refractive index, and 0.019 (0.068) for the single‐scattering albedo. These errors represent a reduction from their counterparts in scenario I1 of 79% (57%), 76% (49%), 69% (52%), 66% (46%), and 49% (20%), respectively. We further investigated those retrieval errors over a variety of aerosol loading and fine‐/coarse‐mode prevalence, which indicates that observations in scenario P1 can yield the retrieval of refractive index and single‐scattering albedo for both fine and coarse aerosol modes, when aerosol optical depth at 440 nm is larger than 0.2 and 870/1020 nm Ångström exponent ranges between 0.7 and 1.6.

Global aerosol mixtures and their multiyear and seasonal characteristics

The optical and microphysical characteristics of distinct aerosol types in the atmosphere are not yet specified at the level of detail required for climate forcing studies. What is even less well known are the characteristics of mixtures of aerosol and, in particular, their precise global spatial distribution. Here, cluster analysis is applied to seven years of 3-hourly, gridded 2.5° × 2° aerosol optical depth data from the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model, one of the most-studied global simulations of aerosol type currently available, to construct a spatial partition of the globe into a finite number of aerosol mixtures. The optimal number of aerosol mixtures is obtained with a k-means algorithm with smart seeding in conjunction with a stopping condition based on applying the ‘law of diminishing returns’ to the norm of the Euclidean distance to provide upper and lower bounds on the number of clusters. Each cluster has a distinct composition in terms of the proportion of biomass burning, sulfate, dust and marine (sea salt) aerosol and this leads rather naturally to a taxonomy for labeling aerosol mixtures. In addition, the assignment of primary colors to constituent aerosol types enables true color-mixing and the production of easy-to-interpret maps of their distribution. The mean multiyear global partition as well as partitions deduced on the seasonal timescale are used to extract aerosol robotic network (AERONET) Level 2.0 Version 2 inversion products in each cluster for estimating the values of key optical and microphysical parameters to help characterize aerosol mixtures. On the multiyear timescale, the globe can be spatially partitioned into 10 distinct aerosol mixtures, with only marginally more variability on the seasonal timescale. In the context of the observational constraints and uncertainties associated with AERONET retrievals, bivariate analysis suggests that mixtures dominated by dust and marine aerosol can be detected with reference to their single scattering albedo and Angstrom exponent at visible wavelengths in conjunction with their fine mode fraction and sphericity. Existing multivariate approaches at classification appear to be more ambiguous. The approach presented here provides gridded (1° × 1°) mean compositions of aeorosol mixtures as well as tentative estimates of mean aerosol optical and microphysical parameters in planetary regions where AERONET sites do not yet exist. Spreadsheets of gridded cluster indices for multiyear and seasonal partitions are provided to facililate further study of the global distribution of aerosol mixtures and possibly for the selection of new AERONET site locations.

Sensitivity of PARASOL multi-angle photopolarimetric aerosol retrievals to cloud contamination

Abstract. An important problem in satellite remote sensing of aerosols is related to the need to perform an adequate cloud screening. If a cloud screening is applied that is not strict enough, the ground scene has the probability of residual cloud cover which causes large errors on the retrieved aerosol parameters. On the other hand, if the cloud-screening procedure is too strict, too many clear sky cases, especially near-cloud scenes, will falsely be flagged cloudy. The detrimental effects of cloud contamination as well as the importance of aerosol cloud interactions that can be studied in these near-cloud scenes call for new approaches to cloud screening. Multi-angle multi-wavelength photopolarimetric measurements have a unique capability to distinguish between scattering by (liquid) cloud droplets and aerosol particles. In this paper the sensitivity of aerosol retrievals from multi-angle photopolarimetric measurements to cloud contamination is investigated and the ability to intrinsically filter the cloud-contaminated scenes based on a goodness-of-fit criteria is evaluated. Hereto, an aerosol retrieval algorithm is applied to a partially clouded over-ocean synthetic data set as well as non-cloud-screened over-ocean POLDER-3/PARASOL observations. It is found that a goodness-of-fit filter, together with a filter on the coarse mode refractive index (mrcoarse > 1.335) and a cirrus screening, adequately rejects the cloud-contaminated scenes. No bias or larger SD are found in the retrieved parameters for this intrinsic cloud filter compared to the parameters retrieved in a priori cloud-screened data set (using MODIS/AQUA cloud masks) of PARASOL observations. Moreover, less high-aerosol load scenes are misinterpreted as cloud contaminated. The retrieved aerosol optical thickness, single scattering albedo and Ångström exponent show good agreement with AERONET observations. Furthermore, the synthetic retrievals give confidence in the ability of the algorithm to correctly retrieve the micro-physical aerosol parameters.

Nephelometric method for measuring mass concentrations of urban aerosols and their respirable fractions

A method is suggested for determining the mass concentration of airborne particles with sizes ≤1, ≤2.5, ≤10, and >10 μm by measuring the light scattering coefficients of the investigated air at the wavelengths λ1 ≤ 0.55 and λ2 ≥ 1.0 μm for the scattering angles θ1 ≤ 5° and θ2 = 15–45°. Mass concentrations of airborne particles are calculated on the basis of their stable statistical relationships with measured coefficients. Analytical expressions for approximation of these statistical relationships have been derived on the basis of an optical-microphysical model of urban aerosol, adopted by the World Meteorological Organization, with variable concentrations, size distribution parameters, and complex refractive index of the particles of aerosol components (soot, water-soluble, and dust). Statistical relationships derived in the modeling approach have been compared with independent numerical and experimental data. The errors of the method developed have been assessed under the overall variability of urban aerosol microphysical parameters.

Relationship between black carbon and associated optical, physical and radiative properties of aerosols over two contrasting environments

The first simultaneous aethalometer and solar radiometer measurements of black carbon (BC) mass concentration (surface-level) and aerosol optical, microphysical and radiative parameters (columnar) have been made during 2005–2011 over two contrasting experimental sites, one representing background rural environment (Sinhagad) and the other surrounded by urban environment (Pune) in the south-west India. The long-term diurnal cycle of BC aerosols over both sites exhibited a strong peak during daytime and a weaker plateau around evening–midnight hours, implying the influence of anthropogenic emissions as well as changes in planetary boundary layer (PBL). The multi-year seasonal mean variation in BC concentration shows the highest during winter and lowest during monsoon seasons, which is found to be inversely related to the variations in single scattering albedo (SSA). Moreover, the BC variations were found to be strongly associated with greater values of Angstrom exponent (α), indicating that the observed BC involves abundance of fine-mode aerosol fraction. The higher concentrations of BC during winter and lower concentrations during pre-monsoon over both Pune and Sinhagad are noticed to be closely linked with aerosol optical depth, revealing significant contribution of BC to the composite aerosol over both the regions. The columnar AOD and Angstrom exponent also showed relatively greater optical depth and α values during winter as compared to pre-monsoon season over both sites.

Sensitivity analysis of single-angle polarization reflectance observed by satellite

Two channels of the Cloud Aerosol Polarimetric Imager, onboard the TanSat-Chinese carbon dioxide observation satellite, are designed to detect the polarization state of radiation reflected by the earth-atmosphere system in a single-viewing angle. Aiming to understand how the earth and atmospheric parameters affect the polarization state of radiation, we conduct a sensitivity analysis of the polarized reflectance at the top of atmosphere (TOA) with respect to the aerosol microphysical parameters, atmospheric profiles, and surface polarization properties. It is found that (1) the TOA polarization reflectance at 0.66 μm is most sensitive to the real part of the aerosol complex refractive index, the mean radius of the fine mode aerosol particles, as well as atmospheric pressure and temperature profiles; (2) the TOA polarization reflectance at 1.64 μm is sensitive to the volume ratio between the coarse mode and fine mode particles as well, but it is not sensitive to atmospheric profiles; and (3) surface polarization properties have a relatively weak influence on the TOA polarization reflectance at both 0.66 and 1.64 μm.

Statistical analysis of single-track instrument sampling in spaceborne aerosol remote sensing for climate research

We examine likely effects of pixel-wide along-track sampling on climatological means of aerosol optical thickness (AOT) derived from observations with satellite instruments such as CALIOP and APS by sub-sampling AOT retrievals from a wide-swath imaging instrument (MODIS). The advantage of using daily pixel-level aerosol retrievals from MODIS rather than aerosol transport models to assess the results of along-track sampling is that limitations caused by the presence of clouds are implicit in the satellite dataset, so that their seasonal and regional variations are captured coherently. However, imager data can exhibit latitudinal (cross-track) variability of monthly global mean AOTs caused by a scattering-angle dependence. This makes it difficult to separate natural variability from viewing-geometry artifacts complicating direct comparisons of an along-track sub-sample with the full imager data. To work around this problem, we introduce “latitudinal-track” sampling which, by design, captures the cross-track AOT variability of the original imager data. We show that the latitudinal-track standard error of global monthly mean AOTs is much smaller than the longitudinal-track one. This allows us to attribute the difference between the two errors to MODIS viewing-geometry artifacts and obtain an upper limit on AOT errors caused by along-track sampling. We conclude that single-track instruments provide AOT sampling sufficient for climate applications. Since AOT is believed to be the most variable characteristic of tropospheric aerosols, our results imply that pixel-wide along-track coverage also provides adequate statistical representation of the global distribution of aerosol microphysical parameters.

Method for determining microphysical parameters of atmospheric aerosol from the results of satellite and ground-based multifrequency sounding

A method for reconstructing the parameters of postvolcanic stratospheric aerosol from the results of joint measurements of the aerosol backscattering coefficient with lidar systems based on the Nd:YAG laser and the aerosol extinction coefficient with the SAGE III satellite instrumentation is developed. The most informative set of optical characteristics is determined for each of the microphysical parameters under consideration (concentration, surface area, volume, and effective size of particles of the fine and coarse aerosol fractions). Multiple polynomial regressions between optical and microphysical characteristics of aerosol are obtained. These regressions make it possible to determine the microphysical characteristics of aerosol within a wide range without solving incorrect inverse problems. The results are compared with independent experimental data. The errors of reconstructing microphysical parameters of aerosol are estimated for different situations in the stratosphere. The influence of the shape of particles of the dust fraction on the results of a reconstruction of the microphysical parameters of aerosol is considered.

Comparative study of aircraft- and satellite-derived aerosol and cloud microphysical parameters during CAIPEEX-2009 over the Indian region

This article presents the spatial and vertical distribution of aerosols and cloud microphysical parameters from the combined data sets of aircraft and satellites. The aircraft-based Cloud Aerosol Interactions and Precipitation Enhancement Experiment (CAIPEEX) was conducted in India during May to September 2009. During the experimental period, 3 days were identified on which space-borne lidar (CALIPSO) and radar (CloudSat) were nearby/over passed the observational regions, which covered north, south central, and southern parts of the Indian subcontinent. The results obtained from these three cases are explored. Similar features of aerosol layering and water/ice cloud signatures are observed by both aircraft and CALIPSO. In addition, events where dust aerosols acting as ice nuclei and polluted aerosols increase the depth of warm rain initiation are observed. The CloudSat profiles of liquid water content, droplet number concentration, and effective radii are underestimated when compared with the corresponding aircraft profiles. The aircraft measurements are able to bring out fine variability in vertical distribution, which would be more useful for regional parameterization schemes and model evaluation.

Spatial variation of aerosol optical properties around the high-alpine site Jungfraujoch (3580 m a.s.l.)

Abstract. This paper presents results of the extensive field campaign CLACE 2010 (Cloud and Aerosol Characterization Experiment) performed in summer 2010 at the Jungfraujoch (JFJ) and the Kleine Scheidegg (KLS) in the Swiss Alps. The main goal of this campaign was to investigate the vertical variability of aerosol optical properties around the JFJ and to show the consistency of the different employed measurement techniques considering explicitly the effects of relative humidity (RH) on the aerosol light scattering. Various aerosol optical and microphysical parameters were recorded using in-situ and remote sensing techniques. In-situ measurements of aerosol size distribution, light scattering, light absorption and scattering enhancement due to water uptake were performed at the JFJ at 3580 m a.s.l.. A unique set-up allowed remote sensing measurements of aerosol columnar and vertical properties from the KLS located about 1500 m below and within the line of sight to the JFJ (horizontal distance of approx. 4.5 km). In addition, two satellite retrievals from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the Moderate Resolution Imaging Spectroradiometer (MODIS) as well as back trajectory analyses were added to the comparison to account for a wider geographical context. All in-situ and remote sensing measurements were in clear correspondence. The ambient extinction coefficient measured in situ at the JFJ agreed well with the KLS-based LIDAR (Light Detection and Ranging) retrieval at the altitude-level of the JFJ under plausible assumptions on the LIDAR ratio. However, we can show that the quality of this comparison is affected by orographic effects due to the exposed location of the JFJ on a saddle between two mountains and next to a large glacier. The local RH around the JFJ was often higher than in the optical path of the LIDAR measurement, especially when the wind originated from the south via the glacier, leading to orographic clouds which remained lower than the LIDAR beam. Furthermore, the dominance of long-range transported Saharan dust was observed in all measurements for several days, however only for a shorter time period in the in-situ measurements due to the vertical structure of the dust plume. The optical properties of the aerosol column retrieved from SEVIRI and MODIS showed the same magnitude and a similar temporal evolution as the measurements at the KLS and the JFJ. Remaining differences are attributed to the complex terrain and simplifications in the aerosol retrieval scheme in general.

An Advanced Model for the Estimation of the Surface Solar Irradiance Under All Atmospheric Conditions Using MSG/SEVIRI Data

A new advanced model for estimation of surface solar irradiance from satellite (AMESIS), designed to estimate with better accuracy the incident solar radiation at the surface from the spinning enhanced visible and infrared imager (SEVIRI) satellite measurements, has been developed. The new generations of sensors such as SEVIRI payload on board the geostationary meteosat second generation gives an opportunity to improve the solar irradiance estimation at surface with accuracy as well as the high spatial and time resolution for a large geographical area according to the needs of solar energy applications. The model developed takes into account the effect of aerosol, the overcast and partially cloudy coverage, and provides irradiance solar maps every 15 min both for monitoring purposes and for monthly, annual averages of surface solar irradiance. Cloud and aerosol microphysical parameters are retrieved by using VIS and IR SEVIRI channels, while surface solar irradiance is retrieved through the high-resolution broadband visible channel. Comparisons with the Global Atmosphere Watch station ground-based measurements of incoming solar radiation agree with the values retrieved with AMESIS model. The results show a very good correlation of about 0.99, a root mean square and a bias ranging, respectively, between 1 and 2.7 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and -0.6 and 0.4 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> depending on the station.

Two-stream approximation for rapid modeling the light pollution levels in local atmosphere

The two-stream concept is used for modeling the radiative transfer in Earth’s atmosphere illuminated by ground-based light sources. The light pollution levels (illuminance and irradiance) are computed for various aerosol microphysical parameters, specifically the asymmetry parameter gA, single scattering albedo ωA, and optical thickness τA. Two distinct size distributions of Junge’s and gamma-type are employed. Rather then being a monotonic function of τA, the diffuse illuminance/irradiance shows a local minimum at specific τA,lim independent of size distribution taken into consideration. The existence of local minima has relation to the scattering and attenuation efficiencies both of which have opposite effects. The computational scheme introduced in this paper is advantageous especially if the entire set of calculations needs to be repeated with an aim to simulate diffuse light in various situations and when altering optical states of the atmospheric environment.

Polarimetric retrievals of surface and cirrus clouds properties in the region affected by the Deepwater Horizon oil spill

In 2010, the Goddard Institute for Space Studies (GISS) Research Scanning Polarimeter (RSP) performed several aerial surveys over the region affected by the oil spill caused by the explosion of the Deepwater Horizon offshore platform. The instrument was deployed on the NASA Langley B200 aircraft together with the High Spectral Resolution Lidar (HSRL), which provides information on the distribution of the aerosol layers beneath the aircraft, including an accurate estimate of aerosol optical depth.This work illustrates the merits of polarization measurements in detecting variations of ocean surface properties linked to the presence of an oil slick. In particular, we make use of the degree of linear polarization in the glint region, which is severely affected by variations in the refractive index but insensitive to the waviness of the water surface. Alterations in the surface optical properties are therefore expected to directly affect the polarization response of the RSP channel at 2264nm, where both molecular and aerosol scattering are negligible and virtually all of the observed signal is generated via Fresnel reflection at the surface. The glint profile at this wavelength is fitted with a model which can optimally estimate refractive index, wind speed and direction, together with aircraft attitude variations affecting the viewing geometry. The retrieved refractive index markedly increases over oil-contaminated waters, while the apparent wind speed is significantly lower than in adjacent uncontaminated areas, suggesting that the slick dampens high-frequency components of the ocean wave spectrum.The constraint on surface reflectance provided by the short-wave infrared channels is a cornerstone of established procedures to retrieve atmospheric aerosol microphysical parameters based on the inversion of the RSP multispectral measurements. This retrieval, which benefits from the ancillary information provided by the HSRL, was in this specific case hampered by prohibitive variability in atmospheric conditions (very inhomogeneous aerosol distribution and cloud cover). Although the results presented for the surface are essentially unaffected, we discuss the results obtained by typing algorithms in sorting the complex mix of aerosol types, and show evidence of oriented ice in cirrus clouds present in the area. In this context, polarization measurements at 1880nm were used to infer ice habit and cirrus optical depth, which was found in the subvisual/threshold-visible regime, confirming the utility of the aforementioned RSP channel for the remote sensing of even thin cold clouds.

Retrieval of optical and microphysical characteristics of postvolcanic stratospheric aerosol from the results of three-frequency lidar sensing

A method is developed for retrieving the altitude profiles of optical and microphysical parameters (MPPs) of postvolcanic stratospheric aerosol (SA) from atmospheric remote sensing data at wavelengths of 355, 532 and 1064 nm. The method uses robust multiple regressions between optical SA characteristics derived from the statistical optical-microphysical SA model to retrieve the profiles of the aerosol backscattering coefficient (ABSC) at the mentioned wavelengths. The inverse problem is solved using polynomial multiple regressions between aerosol integral MPPs and spectral ABSC values. Agreement with independent experimental data confirms the reliability of the derived regressions. We present the results of numerical experiments on retrieving ABSC and aerosol MPP profiles corresponding to different states of the postvolcanic stratosphere.

The influence of the microphysical parameters of atmospheric aerosol particles on IR radiation extinction

The influence of the aerosol component on the total transmission of sounding IR radiation is analyzed. The emissions of both industrial and natural origins into the atmosphere were regarded as the medium. It is noted that, in studying the radiative transport through gas-aerosol mixtures, it is necessary to take into account both molecular absorption and scattering from aerosol particles. It is shown that there are certain boundary values of the microphysical parameters of aerosol where it is sufficient to take into account only one of the above-mentioned factors of radiation extinction. The quantitative values of the parameters of an aerosol medium, on the basis of which the solution of the transport equation can be significantly simplified, are given.

Estimation of the test measurement accuracy in problems of optical diagnostics of aerosol microphysical parameters

The a priori information accumulated on atmospheric aerosols is considered in application to the problems of the analysis of the informativity of measurements of different optical aerosol characteristics for microphysical aerosol parameters. The necessity of modeling the microphysical variations describing the actual aerosol variability is noted. Based on these principles, a statistical microphysical model of ground aerosols is proposed. Using the model, the variational coefficients of optical aerosol characteristics as functions of the microphysical parameters are calculated. They are incorporated into a computer database and the corresponding computation code. The above computational means are applicable for different problems regarding the analysis of the informativity of the measurements of optical aerosol characteristics, in particular, the estimation of the necessary accuracy of simultaneous (test) microphysical ones. As an example, estimates of the informativity of particular lidar measurements are considered for which regression relations between the optical and microphysical parameters were obtained in the framework of numerical experiments. A good agreement between the retrieved aerosol parameters by the proposed regression relations and the corresponding AERONET data has been shown.