Smoke aerosol properties and ageing effects for northern temperate and boreal regions derived from AERONET source and age attribution

• Published in: Atmospheric chemistry and physics 2015-07, Vol.15 (14), p.7929-7943
• Main Authors: Nikonovas, T, North, P R J, Doerr, S H
• Format: Article
• Language: English
• Subjects: Active satellites; Aerosol models; Aerosol observations; Aerosol properties; Aerosols; Age; Ageing; Aging; Aging (natural); Agricultural land; Air pollution; Albedo; Algorithms; Along track scanning radiometer; Biomass; Boreal forests; Climate effects; Climate models; Coniferous forests; Emissions; Emissions (Pollution); Endangered & extinct species; Extinction; Fires; Forest & brush fires; Forests; Grasslands; Land cover; Methods; Mixed forests; Modelling; Natural vegetation; Optical properties; Optical thickness; Particle size; Particulate emissions; Plumes; Prescribed fire; Radiometers; Remote sensing; Retrieval; Satellites; Savannahs; Scattering; Smoke; Spectroradiometers; Studies; Wildfires
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-15-7929-2015

Particulate emissions from wildfires impact human health and have a large but uncertain effect on climate. Modelling schemes depend on information about emission factors, emitted particle microphysical and optical properties and ageing effects, while satellite retrieval algorithms make use of characteristic aerosol models to improve retrieval. Ground-based remote sensing provides detailed aerosol characterisation, but does not contain information on source. Here, a method is presented to estimate plume origin land cover type and age for AERONET aerosol observations, employing trajectory modelling using the HYSPLIT model, and satellite active fire and aerosol optical thickness (AOT) observations from Moderate Resolution Imaging Spectroradiometer (MODIS) and Along Track Scanning Radiometer (AATSR). It is applied to AERONET stations located in or near northern temperate and boreal forests for the period 2002-2013. The results from 629 fire attributions indicate significant differences in size distributions and particle optical properties between different land cover types and plume age. Smallest fine mode median radius (Rfv) are attributed to plumes from cropland and/or natural vegetation mosaic (0.143 mu m) and grassland (0.157 mu m) fires. North American evergreen needleleaf forest emissions show a significantly smaller Rfv (0.164 mu m) than plumes from Eurasian mixed forests (0.193 mu m) and plumes attributed to the land cover types with sparse tree cover - open shrubland (0.185 mu m) and woody savannas (0.184 mu m). The differences in size distributions are related to inferred variability in plume concentrations between the land cover types. Significant differences are observed between day and night emissions, with daytime emissions showing larger particle sizes. Smoke is predominantly scattering for all of the classes with median single scattering albedo at 440 nm (SSA(440)) values close to 0.95 except the cropland emissions which have an SSA(440) value of 0.9. Plumes aged for 4 days or older have median Rfv larger by ~0.02 mu m compared to young smoke. Differences in size were consistent with a decrease in the Aangstrom Exponent and increase in the asymmetry parameter. Only an insignificant increase in SSA( lambda ) with ageing was found.