Particle Extinction Coefficient Research Articles

Theoretical Estimation of Extinction Coefficient Due to Time Evolution of Particle Size Distribution

The extinction coefficient of atmospheric aerosol particles influences the earth's radiation balance directly or indirectly and it can be determined by the scattering and absorption characteristics of aerosol particles. The problem of estimating the change of extinction coefficient due to time evolution of particle size distribution is studied and an improved method for calculating the single particle extinction efficiency is proposed. Through this improved method, the single particle extinction efficiency can be expressed simply in powers of particle diameter based on the anomalous diffraction approximate for the particle size range from 0.1 to 10 µm in diameter first, and then the change of the overall extinction coefficient undergoing (individually and simultaneous) Brownian and gravitational coagulation as well as condensation can be estimated comprehensively with the moment method based on the general dynamic equation. The feasibility and reliability of this method are investigated and the effect of time evolution of particle size distribution on the extinction coefficient is also estimated systemically. Simulation experiments indicate that the extinction coefficient obtained with the improved method coincides fairly well with that using the Mie theory, which provides a simple, dependable, and efficient method to estimate the change of extinction coefficient during the particle dynamic processes.

Characterizing the vertical profile of aerosol particle extinction and linear depolarization over Southeast Asia and the Maritime Continent: The 2007–2009 view from CALIOP

Vertical profiles of 0.532μm aerosol particle extinction coefficient and linear volume depolarization ratio are described for Southeast Asia and the Maritime Continent. Quality-screened and cloud-cleared Version 3.01 Level 2 NASA Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) 5-km Aerosol Profile datasets are analyzed from 2007 to 2009. Numerical simulations from the U.S. Naval Aerosol Analysis and Predictive System (NAAPS), featuring two-dimensional variational assimilation of NASA Moderate Resolution Imaging Spectroradiometer and Multi-angle Imaging SpectroRadiometer quality-assured datasets, combined with regional ground-based lidar measurements, are considered for assessing CALIOP retrieval performance, identifying bias, and evaluating regional representativeness. CALIOP retrievals of aerosol particle extinction coefficient and aerosol optical depth (AOD) are high over land and low over open waters relative to NAAPS (0.412/0.312 over land for all data points inclusive, 0.310/0.235 when the per bin average is used and each is treated as single data points; 0.102/0.151 and 0.086/0.124, respectively, over ocean). Regional means, however, are very similar (0.180/0.193 for all data points and 0.155/0.159 when averaged per normalized bin), as the two factors offset one another. The land/ocean offset is investigated, and discrepancies attributed to interpretation of particle composition and a-priori assignment of the extinction-to-backscatter ratio (“lidar ratio”) necessary for retrieving the extinction coefficient from CALIOP signals. Over land, NAAPS indicates more dust present than CALIOP algorithms are identifying, indicating a likely assignment of a higher lidar ratio representative of more absorptive particles. NAAPS resolves more smoke over water than identified with CALIOP, indicating likely usage of a lidar ratio characteristic of less absorptive particles to be applied that biases low AOD there. Over open waters except within the Bay of Bengal, aerosol particle scattering is largely capped below 1.5km MSL, though ground-based lidar measurements at Singapore differ slightly from this finding. Significant aerosol particle presence over land is similarly capped near 3.0km MSL over most regions. Particle presence at low levels regionally, except over India, is dominated by relatively non-depolarizing particles. Industrial haze, sea salt droplets and fresh smoke are thus most likely present.

Seasonal variations of aerosol optical properties, vertical distribution and associated radiative effects in the Yangtze Delta region of China

Four years of columnar aerosol optical properties and a one‐year vertical profiles of aerosol particle extinction coefficient at 527 nm are analyzed at Taihu in the central Yangtze River Delta region in eastern China. Seasonal variations of aerosol optical properties, vertical distribution, and influence on shortwave radiation and heating rates were investigated. Multiyear variations of aerosol optical depths (AOD), Ångstrom exponents, single scattering albedo (SSA) and asymmetry factor (ASY) are analyzed, together with the vertical profile of aerosol extinction. AOD is largest in summer and smallest in winter. SSAs exhibit weak seasonal variation with the smallest values occurring during winter and the largest during summer. The vast majority of aerosol particles are below 2 km, and about 62%, 67%, 67% and 83% are confined to below 1 km in spring, summer, autumn and winter, respectively. Five‐day back trajectory analyses show that the some aerosols aloft are traced back to northern/northwestern China, as far as Mongolia and Siberia, in spring, autumn and winter. The presence of dust aerosols were identified based on the linear depolarization measurements together with other information (i.e., back trajectory, precipitation, aerosol index). Dust strongly impacts the vertical particle distribution in spring and autumn, with much smaller effects in winter. The annual mean aerosol direct shortwave radiative forcing (efficiency) at the bottom, top and within the atmosphere are −34.8 ± 9.1 (−54.4 ± 5.3), −8.2 ± 4.8 (−13.1 ± 1.5) and 26.7 ± 9.4 (41.3 ± 4.6) W/m2 (Wm−2 τ−1), respectively. The mean reduction in direct and diffuse radiation reaching surface amount to 109.2 ± 49.4 and 66.8 ± 33.3 W/m2, respectively. Aerosols significantly alter the vertical profile of solar heating, with great implications for atmospheric stability and dynamics within the lower troposphere.

Preparation and characterization of polysilsesquioxane particles containing UV-absorbing groups

Organotrialkoxysilanes (OTAS) containing bulky UV chromophores were polymerized under basic conditions to prepare insoluble spherical polysilsesquioxane (PSQ) particles potentially useful as UV blocking ingredients in sunscreens. The OTAS used in this study were 3-aminopropyltrimethoxysilyl-p-methoxycinnamamide (APTMSMCA), 3-aminopropyltriethoxysilyl-p-ethoxycinnamamide (APTESMCA), 3-aminopropyltrimethoxysilyl-p-N,N′-dimethylaminobezamide (APTMSDMABA), and 3-aminopropyltriethoxysilyl-p-N,N′-dimethylaminobenzamide (APTESDMABA). Mixtures of insoluble spherical particles, soluble solids, and insoluble monolithic solids were produced in various yields depending on the reaction conditions and the nature of the chromophore. The molar extinction coefficients of PSQ particles were 1/2 to 1/4 of those of corresponding unreacted chromophores and OTAS. The λ max and extinction coefficients of the PSQ particles varied according to their sizes. In vitro sun protection factor (SPF) values of petrolatum containing 10 wt% of the particles were between 10 and 21. The photostability of polyAPTMSMCA and polyAPTMSDMABA particles were significantly poorer than those of APTMSMCA and APTMSDMABA. Copolymerization of APTMSDMABA and methyltrimethoxysilane (MTMS) significantly improved the photostability. The particles dispersed in water and silicon oil showed photomechanical effects under UV light that were most likely caused by heat released during the relaxation process.

Research on bimodal particle extinction coefficient during Brownian coagulation and condensation for the entire particle size regime

The extinction coefficient of atmospheric aerosol particles influences the earth’s radiation balance directly or indirectly, and it can be determined by the scattering and absorption characteristics of aerosol particles. The problem of estimating the change of extinction coefficient due to time evolution of bimodal particle size distribution is studied, and two improved methods for calculating the Brownian coagulation coefficient and the condensation growth rate are proposed, respectively. Through the improved method based on Otto kernel, the Brownian coagulation coefficient can be expressed simply in powers of particle volume for the entire particle size regime based on the fitted polynomials of the mean enhancement function. Meanwhile, the improved method based on Fuchs–Sutugin kernel is developed to obtain the condensation growth rate for the entire particle size regime. And then, the change of the overall extinction coefficient of bimodal distributions undergoing Brownian coagulation and condensation can be estimated comprehensively for the entire particle size regime. Simulation experiments indicate that the extinction coefficients obtained with the improved methods coincide fairly well with the true values, which provide a simple, reliable, and general method to estimate the change of extinction coefficient for the entire particle size regime during the bimodal particle dynamic processes.

Further evidence for significant smoke transport from Africa to Amazonia

[1] Polarization-Raman-lidar observations of vertical aerosol profiles were performed 60 km north of Manaus, Brazil, in the Amazon rain forest during Amazonia's wet season from January to May 2008. Very clean background conditions with a mean AOD (532 nm) of 0.03 ± 0.02 were frequently found. However, in about one third of all lidar measurements advection of smoke and dust aerosol from Africa were observed. The contribution of African smoke and Saharan dust particles to the total backscatter and extinction coefficient was determined by means of the measured particle depolarization ratio. A decreasing contribution of smoke particles to the total particle extinction coefficient from values around 60%–80% in January and February 2008, to values of 0%–50% in May 2008 was observed. Smoke–related extinction coefficients and optical depths up to 80 Mm−1 and 0.15 at 532 nm, respectively, were recorded.

Lidar ratio of Saharan dust over Cape Verde Islands: Assessment and error calculation

[1] Lidar ratios Sp of Saharan dust were determined at the Cape Verde Islands in the framework of the second phase of the Saharan Mineral Dust Experiment to investigate possible changes during the first few days of transport from the source regions. Lidar ratios were retrieved from vertical profiles of particle extinction coefficients and backscatter coefficients measured simultaneously at 355 and 532 nm with the two Raman lidar systems MULIS and POLIS of the Meteorological Institute of the Ludwig-Maximilians-Universitat. As previous studies are lacking, one of the main foci of this paper is the elaboration of an extensive error analysis of the Sp retrieval. Only the determination of systematic errors, resulting from the uncertainties of the input parameters of the retrieval, and statistical errors of Sp due to signal noise allows one to compare measurements at different sites and to gain insight into the changes of the dust lidar ratio with time. Suitable conditions for the assessment of Sp and the error analysis were met during a strong Saharan dust outbreak from 28 to 30 January 2008, where particle extinction coefficients of the dust layer as high as 0.2–0.4 km−1 in the UV and visible spectral region were observed. We found an average lidar ratio of dust over Cape Verde Islands of 63 ± 6 sr at 355 and 532 nm.

An Analysis of Extinction Coefficients of Particles and Water Moisture in the Stack after Flue Gas Desulfurization at a Coal-Fired Power Plant

ABSTRACT Two important factors that affect in-stack opacity—light extinction by emitted particles and that by water moisture after a flue gas desulfurization (FGD) unit—are investigated. The mass light extinction coefficients for particles and water moisture, k p and k w, respectively, were determined using the Lambert-Beer law of opacity with a nonlinear least-squares regression method. The estimated k p and k w values vary from 0.199 to 0.316 m2/g and 0.000345 to 0.000426 m2/g, respectively, and the overall mean estimated values are 0.229 and 0.000397 m2/g, respectively. Although k w is 3 orders of magnitude smaller than k p, experimental results show that the effect on light extinction by water moisture was comparable to that by particles because of the existence of a considerable mass of water moisture after a FGD unit. The mass light extinction coefficient was also estimated using Mie theory with measured particle size distributions and a complex refractive index of 1.5-ni for fly ash particles. The k p obtained using Mie theory ranges from 0.282 to 0.286 m2/g and is slightly greater than the averaged estimated k p of 0.229 m2/g from measured opacity. The discrepancy may be partly due to a difference in the microstructure of the fly ash from the assumption of solid spheres because the fly ash may have been formed as spheres attached with smaller particles or as hollow spheres that contained solid spheres. Previously reported values of measured k p obtained without considering the effects of water moisture are greater than that obtained in this study, which is reasonable because it reflects the effect of extinction by water moisture in the flue gas. Additionally, the moisture absorbed by particulate matter, corresponding to the effect of water moisture on the particulates, was clarified and found to be negligible. IMPLICATIONS In-stack opacity is used as a surrogate for particle concentration and can be measured using light transmission meters as part of a continuous emission monitoring system. Because emission standards have become increasingly strict, FGD with wet scrubbing is generally used for coal-fired power plants. However, after a FGD unit with wet scrubbing is set up, the concentration of water moisture increases, affecting the measured opacity. This study evaluates the contributions of particles and water moisture to opacity. The results should provide useful information and can be utilized for modifying measurements for monitoring particulate emissions using opacity.

First long-term study of particle number size distributions and new particle formation events of regional aerosol in the North China Plain

Abstract. Atmospheric particle number size distributions (size range 0.003–10 μm) were measured between March 2008 and August 2009 at Shangdianzi (SDZ), a rural research station in the North China Plain. These measurements were made in an attempt to better characterize the tropospheric background aerosol in Northern China. The mean particle number concentrations of the total particle, as well as the nucleation, Aitken, accumulation and coarse mode were determined to be 1.2 ± 0.9 × 104, 3.6 ± 7.9 × 103, 4.4 ± 3.4 × 103, 3.5 ± 2.8 × 103 and 2 ± 3 cm−3, respectively. A general finding was that the particle number concentration was higher during spring compared to the other seasons. The air mass origin had an important effect on the particle number concentration and new particle formation events. Air masses from northwest (i.e. inner Asia) favored the new particle formation events, while air masses from southeast showed the highest particle mass concentration. Significant diurnal variations in particle number were observed, which could be linked to new particle formation events, i.e. gas-to-particle conversion. During particle formation events, the number concentration of the nucleation mode rose up to maximum value of 104 cm−3. New particle formation events were observed on 36% of the effective measurement days. The formation rate ranged from 0.7 to 72.7 cm−3 s−1, with a mean value of 8.0 cm−3 s−1. The value of the nucleation mode growth rate was in the range of 0.3–14.5 nm h−1, with a mean value of 4.3 nm h−1. It was an essential observation that on many occasions the nucleation mode was able to grow into the size of cloud condensation nuclei (CCN) within a matter of several hours. Furthermore, the new particle formation was regularly followed by a measurable increase in particle mass concentration and extinction coefficient, indicative of a high abundance of condensable vapors in the atmosphere under study.

Airborne spectral radiation measurements to derive solar radiative forcing of Saharan dust mixed with biomass burning smoke particles

Airborne measurements of upward solar spectral irradiances were performed during the second Saharan Mineral dUst experiMent (SAMUM-2) campaign based on the Cape Verde Islands. Additionally, airborne high resolution lidar measurements of vertical profiles of particle extinction coefficients were collected in parallel to the radiation data. Aerosol layers of Saharan dust, partly mixed with biomass-burning smoke, were probed. With corresponding radiative transfer simulations the single scattering albedo and the asymmetry parameter of the aerosol particles were derived although with high uncertainty. The broad-band aerosol solar radiative forcing at the top of atmosphere was calculated and examined as a function of the aerosol types. However, due to uncertainties in both the measurements and the calculations the chemical composition cannot be identified. In addition, a mostly measurement-based method to derive the broad-band aerosol solar radiative forcing was used. This approach revealed clear differences of broad-band net irradiances as a function of the aerosol optical depth. The data were used to identify different aerosol types from different origins. Higher portions of biomass-burning smoke lead to larger broad-band net irradiances.

Size matters: Influence of multiple scattering on CALIPSO light‐extinction profiling in desert dust

We investigate the discrepancies in measurements of light extinction and extinction‐to‐backsatter ratio (lidar ratio) of desert dust with CALIPSO and ground‐based lidar systems. Multiwavelength polarization Raman lidar measurements in the Saharan dust plume performed at Praia, Cape Verde, 15.0°N, 23.5°W, during SAMUM–2 in June 2008 were analyzed and compared to results of nearby CALIPSO overflights. The particle extinction coefficients and thus the optical depth are underestimated in the CALIPSO products by about 30% compared to Raman lidar measurements. A pre‐defined lidar ratio of 40 sr at 532 nm is used for mineral dust in the CALIPSO algorithms in agreement with values of 41 ± 6 sr found from constrained retrievals. However, the ground‐based lidar observations show much larger values of the order of 55 ± 10 sr. The discrepancies can be explained by the influence of multiple scattering which is ignored in the CALIPSO retrievals. Based on recent observations of the size distribution of dust particles from airborne in‐situ observations during SAMUM–1, our model calculations show that the multiple‐scattering‐related underestimation of the extinction coefficient in the CALIPSO lidar signals ranges from 10%–40%. We propose a method to overcome this underestimation.

Lidar beams in opposite directions for quality assessment of Cloud-Aerosol Lidar with Orthogonal Polarization spaceborne measurements

We present the "lidar beams in opposite directions" (LIBOD) technique and applications for quality assessment of spaceborne observations made by Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite. LIBOD is applicable to standard total backscatter lidar because it does not require a priori knowledge of the particle extinction-to-backscatter ratio. In this paper, we present (i) an objective assessment of the lidar signal quality and representativity of correlative ground-based lidar and CALIOP measurements only using normalized range-corrected lidar signals and (ii) a numerical filtering and optimization technique for reducing the spurious oscillations induced by noisy signal differentiation as needed for retrieval of particle extinction coefficients and extinction-to-backscatter ratio profiles. Numerical simulations and Monte Carlo tests are conducted for assessing the performance of the LIBOD technique. The applications are illustrated with examples of actual correlative 532 nm lidar profiles from CALIOP and a ground-based lidar deployed in Tamanrasset in the heart of Sahara in 2006 and near Strasbourg, France, in 2007.

On retrieval of lidar extinction profiles using Two-Stream and Raman techniques

Abstract. The Two-Stream technique employs simultaneous measurements performed by two elastic backscatter lidars pointing at each other to sample into the same atmosphere. It allows for a direct retrieval of the extinction coefficient profile from the ratio of the two involved lidar signals. During a number of Alfred-Wegener-Institute (AWI) campaigns dedicated to Arctic research, the AWI's Polar 2 aircraft with the integrated onboard nadir-pointing Airborne Mobile Aerosol Lidar (AMALi) was utilised. The aircraft flew over a vicinity of Ny Ålesund on Svalbard, where the zenith-pointing Koldewey Aerosol Raman Lidar (KARL) has been located. This experimental approach gave the unique opportunity to retrieve the extinction profiles with a rarely used Two-Stream technique against a well established Raman technique. Both methods were applied to data obtained for clean Arctic conditions during the Arctic Study of Tropospheric clouds and Radiation (ASTAR 2004) campaign, and slightly polluted Arctic conditions during the Svalbard Experiment (SvalEx 2005) campaign. Successful comparison of both evaluation tools in different measurement conditions demonstrates sensitivity and feasibility of the Two-Stream method to obtain particle extinction and backscatter coefficients profiles without assumption of their relationship (lidar ratio). The method has the potential to serve as an extinction retrieval tool for KARL or AMALi simultaneous observations with the space borne CALIPSO lidar overpasses during the ASTAR 2007.

Vertical distribution of water-soluble, sea salt, and dust aerosols in the planetary boundary layer estimated from two-wavelength backscatter and one-wavelength polarization lidar measurements in Guangzhou and Beijing, China

Vertical and temporal distributions of water-soluble, sea salt, and dust aerosols in the planetary boundary layer (PBL) were analyzed from two-wavelength (532 and 1064 nm) backscatter and one-wavelength (532 nm) polarization lidar measurements taken at Guangzhou in July 2006 and Beijing in August 2006. We used an algorithm that estimates the extinction coefficients for each aerosol component from the three-channel lidar data. The results revealed water-soluble aerosols, most of which were anthropogenic aerosols, were dominant in both cities. Air pollution events occurred on 12 and 22–24 July in Guangzhou and on 3–11, 16–19, and 23–25 August in Beijing. Differences in temporal variation of extinction coefficient of water-soluble particles ( σ WS) in the lower layers during the air pollution periods were distinct: σ WS was higher in the nighttime at Beijing, whereas σ WS was higher in the daytime in Guangzhou. Meanwhile similar vertical structures of σ WS in the planetary boundary layer were found for both cities: σ WS increased as the altitude increased. We suggest that different mechanisms contributed to the temporal and vertical variations of σ WS in each city: hygroscopic growth mainly enhanced σ WS in the nighttime and at high altitude for Beijing, while the transport of aerosols in the local area mainly enhanced σ WS in the daytime and at high altitude in Guangzhou. Distinct differences were also observed in the sea-salt components in Guangzhou and in the dust components in Beijing. The correlation of the dust concentration and aerosol depolarization ratio implies that internal mixing of water-soluble and dust particles occurred in Beijing during the air pollution periods.

UV Raman lidar measurements of relative humidity for the characterization of cirrus cloud microphysical properties

Abstract. Raman lidar measurements performed in Potenza by the Raman lidar system BASIL in the presence of cirrus clouds are discussed. Measurements were performed on 6 September 2004 in the frame of the Italian phase of the EAQUATE Experiment. The major feature of BASIL is represented by its capability to perform high-resolution and accurate measurements of atmospheric temperature and water vapour, and consequently relative humidity, both in daytime and night-time, based on the application of the rotational and vibrational Raman lidar techniques in the UV. BASIL is also capable to provide measurements of the particle backscatter and extinction coefficient, and consequently lidar ratio (at the time of these measurements, only at one wavelength), which are fundamental to infer geometrical and microphysical properties of clouds. A case study is discussed in order to assess the capability of Raman lidars to measure humidity in presence of cirrus clouds, both below and inside the cloud. While air inside the cloud layers is observed to be always under-saturated with respect to water, both ice super-saturation and under-saturation conditions are found inside these clouds. Upper tropospheric moistening is observed below the lower cloud layer. The synergic use of the data derived from the ground based Raman Lidar and of spectral radiances measured by the NAST-I Airborne Spectrometer allows the determination of the temporal evolution of the atmospheric cooling/heating rates due to the presence of the cirrus cloud. Lidar measurements beneath the cirrus cloud layer have been interpreted using a 1-D cirrus cloud model with explicit microphysics. The 1-D simulations indicate that sedimentation-moistening has contributed significantly to the moist anomaly, but other mechanisms are also contributing. This result supports the hypothesis that the observed mid-tropospheric humidification is a real feature which is strongly influenced by the sublimation of precipitating ice crystals. Results illustrated in this study demonstrate that Raman lidars, like the one used in this study, can resolve the spatial and temporal scales required for the study of cirrus cloud microphysical processes and appear sensitive enough to reveal and quantify upper tropospheric humidification associated with cirrus cloud sublimation.

Portable Raman Lidar PollyXT for Automated Profiling of Aerosol Backscatter, Extinction, and Depolarization

Abstract Two versions of the portable aerosol Raman lidar system (Polly) are presented. First, the two-channel prototype is depicted. It has been developed for the independent and simultaneous determination of particle backscatter and extinction coefficient profiles at 532 nm. Second, the 3 + 2 Raman lidar PollyXT (3 + 2: three backscatter and two extinction coefficients), the second generation of Polly, is described. The extended capabilities of PollyXT are due to the simultaneous emission of light with three wavelengths, more laser power, a larger main receiver mirror, and seven receiver channels. These systems are completely remotely controlled and all measurements are performed automatically. The collected data are transferred to a home server via the Internet and are displayed on a Web page. This paper describes the details of the optical setup, the housekeeping of the systems, and the used data retrieval routines. A measurement example taken close to Manaus, Brazil, on 15 August 2008 shows the capabilities of PollyXT.

Theoretical study on the change of the particle extinction coefficient during the aerosol dynamic processes

In this study, the effects of aerosol dynamics on the aerosol optical properties were analytically investigated using an approximated expression for the overall extinction coefficient ( b ext ) , which was valid for a wide range of particle size. The processes of both coagulation and condensation in the continuum region were considered using the moment method, with an overall extinction coefficient obtained from the harmonic mean between the overall particle extinction coefficient of the Rayleigh scattering and geometric scattering regions. The derived analytical expressions were compared with the asymptotic expressions of the extinction coefficient, which showed that the obtained expressions ultimately approached the asymptotic expressions. Subsequently, this study showed a simple and straightforward method for estimating the changes in the extinction coefficient and visibility of polydispersed aerosols during aerosol dynamic processes. The accuracy of the approximated overall coefficient was dependent on a given aerosol refractive index and size parameter. Usually, the error was less than 8% for an average size parameter range of 0–80.

Hygroscopic properties and extinction of aerosol particles at ambient relative humidity in South-Eastern China

During the “Program of Regional Integrated Experiments of Air Quality over Pearl River Delta 2004 (PRIDE-PRD2004)” hygroscopic properties of particles in the diameter range 22 nm to 10 μ m were determined. For that purpose, a Humidifying Differential Mobility Particle Sizer (H-DMPS) and a Micro-Orifice Uniform Deposition Impactor (MOUDI) were operated. The derived size-dependent particle hygroscopic growth factors were interpolated to ambient relative humidity (RH) and used to calculate the particle number size distributions (PNSDs) at ambient conditions. A comparison between the modeled particle extinction coefficients ( σ ext , Mie ) and those observed with a Raman lidar was made. It is shown that the particle extinction coefficient ( σ ext ) at ambient RH can be properly estimated with Mie-model calculations based on the in situ physico-chemical measurements of dry and humidified PNSD and chemical composition.

Retrieval of microphysical properties of aerosol particles from one-wavelength Raman lidar and multiwavelength Sun photometer observations

Aerosol Raman lidar observations of particle extinction and backscatter coefficients at 532 nm are combined with Sun photometer observations of the particle optical depth at six wavelengths from 381–1044 nm to derive column-integrated microphysical properties of boundary-layer aerosol such as volume and surface concentrations, effective radius, refractive index, and single scattering albedo. The method is based on our well-tested lidar inversion algorithm and is applied to observations carried out in the heavily polluted Pearl River Delta (PRD), in South China. Different data sets consisting of six extinction coefficients and two backscatter coefficients (measured at 532 nm, estimated at 381 nm), and alternatively, of five extinction coefficients only are used in the inversion retrieval. The results are discussed and compared with ground-based in situ observations of aerosol microphysical properties. Volume concentration, effective radius, real and imaginary part of the refractive index of the particles are determined with a relative uncertainty of 30%, 40%, 10%, and 70%, respectively.

Measurement of the Mass Specific Extinction Coefficient of Acetylene, Toluene and Polymethyl Methacrylate Soot Particles in Visible and Near-Infrared Wavelengths

An experimental set-up has been developed to determine the mass specific σs and the dimensionless extinction Kt coefficients of soot particles at visible (632 nm) and near-infrared (1064 nm) wavelengths. Near-infrared measurements have been carried out with a multiple-path extinction cell to increase the measurement accuracy. The extinction coefficient Kext has been analysed as a function of the mass concentration, measured by a Tapered Element Oscillating Microbalance (TEOM 1105 R&P) in order to retrieve the soot mass specific extinction coefficient, σe, in the smoke plume of acetylene, toluene and PolyMethyl MethAcrylate (PMMA) burning under turbulent, well-ventilated and small-scale conditions. Results for mass specific extinction coefficient σ e are consistent with previous measurements (Mulholland & Croarkin [1] and Newman & Steciak [2]) obtained for a variety of fuels for small-scale fires. The mobility diameter distribution of the soot particles is measured using a Scanning Mobility Particle Sizer (SMPS 3936 TSI). The soot aggregate morphology is determined from Transmission Electronic Microscopy picture analysis. From these measurements, the soot volume fraction is determined and so the dimensionless extinction coefficient. Values at 632 and 1064 nm are given and discussed in comparison to other published data. It is found the scattering contribution to the extinction process is important for the present experimental conditions. For this reason, the use of the dimensionless coefficient is expected to provide a more accurate soot volume fraction value than the calculation which assumes the scattering is negligible.