Characterization of fresh and aged biomass burning events using multiwavelength Raman lidar and mass spectrometry

Abstract

[1] This paper focuses on optical and microphysical properties of long-range transported biomass burning (BB) aerosols and their variation with atmospheric evolution (ageing), as observed by a multiwavelength Raman lidar, part of EARLINET (European Aerosol LIdar NETwork). Chemical analysis of the atmospheric aerosol was done using a colocated aerosol mass spectrometer (AMS). One relevant optical parameter for the ageing process is the Ångström exponent. In our study, we find that it decreases from 2 for fresh to 1.4-0.5 for aged smoke particles. The ratio of lidar (extinction-to-backscatter) ratios (LR 532 /LR 355 ) changes rapidly from values <1 for fresh to >1 for aged particles. The imaginary part of the refractive index is the most sensitive microphysical parameter. It decreases sharply from 0.05 to less than 0.01 for fresh and aged smoke particles, respectively. Singlescattering albedo (SSA) varies from 0.74 to 0.98 depending on aerosol age and source. The AMS was used to measure the marker ions of wood-burning particles during 2 days of measurements when the meteorological conditions favored the downward mixing of aerosols from lofted layers. Particle size distribution and particle effective radius from both AMS and lidar are similar, i.e., particle effective radii were approximately 0.27 mm for fresh BB aerosol particles. Microphysical aerosol properties from inversion of the lidar data agree with similar studies carried out in different regions on the globe. Our study shows that the Ångström exponent LR 532 /LR 355 and the imaginary part of the refractive index can be used to clearly distinguish between fresh and aged smoke particles.

Optical and microphysical characterization of aerosol layers over South Africa by means of multi-wavelength depolarization and Raman lidar measurements

“…The lidar ratios of biomass burning aerosols are among the highest compared to the literature, with a mean value of 92 ± 10 sr (e.g. Müller et al, 2007;Nicolae et al, 2013;Amiridis et al, 2009). Urban/industrial aerosol layers were found to have lower lidar ratio values in the range between 41 and 59 sr at 355 nm.…”

“…found larger biomass burning aerosols with an effective radius of approximately 0.25 µm. Effective radii in the range between 0.19 and 0.44 µm were found for biomass burning aerosol layers resulting from long-range transport across Romania (Nicolae et al, 2013). Müller et al (2007) presented values ranging between 0.13 and 0.15 nm for plumes ageing between 1 and 3 days.…”

“…Lower single-scattering albedos are reported in the literature for fresh biomass burning particles in Europe. Nicolae et al (2013) reported a value of 0.78 ± 0.02, while Reid and Hobbs (1998) found that single-scattering albedo ranges between 0.74 and 0.77 for fresh smoke. Previous studies show that aged biomass burning layers are characterized by larger single-scattering albedos.…”

Are EARLINET and AERONET climatologies consistent? The case of Thessaloniki, Greece

“…In all other cases, the lidar ratio is similar, ranging from 59 to 61 sr. Differences with the summer levels could be attributed to different aerosol transportation paths and thus either more mixing with continental particles or different aging of smoke (e.g., Amiridis et al, 2009;Nicolae et al, 2013;Papayannis et al, 2014). The BAE values are available only for summer and autumn, ranging from 1.3 to 1.4.…”

Lidar Calibration Centre

“…In particular, EARLINET data have been recently used for aerosol characterization in terms of optical and microphysical properties in conjunction with in situ measurements and transport models (e.g. [9], [10], [11], [12]). …”