Optical and microphysical characterization of biomass‐ burning and industrial‐pollution aerosols from‐ multiwavelength lidar and aircraft measurements

Abstract

[1] During the Lindenberg Aerosol Characterization Experiment (LACE 98) simultaneous measurements with ground-based and airborne lidars and with two aircraft equipped with aerosol in situ instrumentation were performed. From the lidar measurements, particle backscatter coefficients at up to eight wavelengths between 320 and 1064 nm and particle extinction coefficients at 2-3 wavelengths between 292 and 532 nm were determined. Thus, for the first time, an extensive set of optical particle properties from several lidar platforms was available for the inversion into particle microphysical quantities. For this purpose, two different inversion algorithms were used, which provide particle effective radius, volume, surface-area, and number concentrations, and complex refractive index. The single-scattering albedo follows from Mie-scattering calculations. The parameters were compared to the ones from airborne measurements of particle size distributions and absorption coefficients. Two measurement cases were selected. During the night of 9 -10 August 1998 measurements were taken in a biomass-burning aerosol layer in the free troposphere, which was characterized by a particle optical depth of about 0.1 at 550 nm. Excellent agreement between remote-sensing and in situ measurements was found. In the center of this plume the effective radius was approximately 0.25 m, and all methods showed rather high complex refractive indices, ranging from 1.56 -1.66 in real part and from 0.05-0.07i in imaginary part. The single-scattering albedo showed low values from 0.78 -0.83 at 532 nm. The second case, taken on 11 August 1998, presents the typical conditions of a polluted boundary layer in central Europe. Optical depth was 0.35 at 550 nm, and particle effective radii were 0.1-0.2 m. In contrast to the first case, imaginary parts of the refractive index were below 0.03i. Accordingly, the single-scattering albedo ranged from 0.87-0.95.

An Adaptive Base Point Algorithm for the Retrieval of Aerosol Microphysical Properties

“…It is worth mentioning here that there is a need for the accurate retrieval of the imaginary part of the aerosols, as it is sometimes very hard to distinguish particles of low refractive index with (m) < 0.01, as stated before. Thus, our retrieved refractive index data by both the mathematical algorithm and the ISORROPIA II model are in good agreement with values reported by several authors for mixing of biomass burning with anthropogenic particles (see [20,22]) where the complex refractive indices ranged from 1.37 up to 1.6 (real part) and the mean imaginary part was always < 0.01i.…”

“…Indeed, in situ measurements of quite fresh biomass burning aerosols during the DABEX experiment in West Africa (see [21]) showed that this type of particles followed a nearly bi-modal size distribution and had preponderant radii of particles of the order of 0.051 0.35 μm, while similar and slightly larger values, including the aging of particles, were found in [20] and [22] over Germany during European and Canadian forest fires. However, it has to be noted that the latter paper [22] tackled the effect of mixing anthropogenic pollution and biomass burning particles, where again bi-modal particle size distributions were found. Therefore, our results on the volume distribution (and thus, the size distribution) and the range of the particle radii are in agreement with previous observations of mixing of biomass burning and anthropogenic particles.…”

Synergetic measurements of aerosols over São Paulo, Brazil using LIDAR, sunphotometer and satellite data during the dry season

“…Similar values of the LR at 532 nm were reported by Mueller et al (2001) and by Wandinger et al (2002) for urban air polluted air masses during the INDOEX experiment. Their discrepancy might be related to the impossibility of having the same time-frame for the data acquisition, besides the figures obtained by the CIMEL oscillate more than 20% in value within few minutes of data acquisition, which might related to the high sensitivity of the CIMEL for the parameters used to obtain the LR, namely the Phase function and Single Scattering Albedo.…”

Airborne high spectral resolution lidar observation of pollution aerosol during EUCAARI-LONGREX

“…Therefore a number of several papers report about measurements within polluted air masses. Lidar ratios of pollution aerosols over Central Europe were reported by Wandinger et al (2002). They found values of 50-65 sr at 532 nm from Raman lidar measurements.…”