Biomass burning aerosol emissions from vegetation fires: particle number and mass emission factors and size distributions

Abstract

Abstract. Aerosol emissions from vegetation fires have a large impact on air quality and climate. In this study, we use published experimental data and different fitting procedures to derive dynamic particle number and mass emission factors (EFPN, EFPM) related to the fuel type, burning conditions and the mass of dry fuel burned, as well as characteristic CO-referenced emission ratios (PN/CO, PM/CO). Moreover, we explore and characterize the variability of the particle size distribution of fresh smoke, which is typically dominated by a lognormal accumulation mode with count median diameter around 120 nm (depending on age, fuel and combustion efficiency), and its effect on the relationship between particle number and mass emission factors. For the particle number emission factor of vegetation fires, we found no dependence on fuel type and obtained the following parameterization as a function of modified combustion efficiency (MCE): EFPN=34×1015×(1−MCE) kg−1±1015 kg−1 with regard to dry fuel mass (d.m.). For the fine particle mass emission factors (EFPM) we obtained (86–85×MCE) g kg−1±3 g kg−1 as an average for all investigated fires; (93–90×MCE) g kg−1±4 g kg−1 for forest; (67–65×MCE) g kg−1±2 g kg−1 for savanna; (63–62×MCE) g kg−1±1 g kg−1 for grass. For the PN/CO emission ratio we obtained an average of (34±16) cm−3 ppb−1 exhibiting no systematic dependence on fuel type or combustion efficiency. The average PM/CO emission ratios were (0.09±0.04) g g−1 for all investigated fires; (0.13±0.05) g g−1 for forest; (0.08±0.03) g g−1 for savanna; and (0.07±0.03) g g−1 for grass. The results are consistent with each other, given that particles from forest fires are on average larger than those from savanna and grass fires. This assumption and the above parameterizations represent the current state of knowledge, but they are based on a rather limited amount of experimental data which should be complemented by further measurements. Nevertheless, the presented parameterizations appear sufficiently robust for exploring the influence of vegetation fires on aerosol particle number and mass concentrations in regional and global model studies.

Aged boreal biomass-burning aerosol size distributions from BORTAS 2011

“…This unimodal result is consistent with aged biomass-burning observations found globally in the previous field studies (Capes et al, 2008;Janhäll et al, 2010;Kondo et al, 2011).…”

“…As the exact aging time and dilution profiles are unknown in addition to uncertainties in the plume age, we cannot say with certainty which of these estimates is best; however, these results compare to the field observations presented in Janhäll et al (2010) for fresh plume smoke (range: D pm = 100-150 nm) and to small-scale lab experiments measuring fresh smoke (range: D pm = 30-90 nm) (Hosseini et al, 2010). Capes et al (2008) conducted a similar fresh-plume size-distribution estimate from their observed DABEX aged African smoke data using a coagulation box model without dilution.…”

“…The aged composite size distribution and associated lognormal parameters are similar to those found in other field studies of aged biomass-burning emissions. Aged biomassburning size distributions compiled by Janhäll et al (2010) for all different fuel types show a similar D pm to modal width ratio (D pm = 175-300 nm, σ = 1.7-1.3). Capes et al (2008) show a similar aged BB size-distribution median diameter over western Africa during the DABEX campaign (D pm = 240 nm).…”

“…Previous studies of field and lab experiments show biomass-burning size distributions vary according to plume age, combustion phase, and fuel type (Adler et al, 2011;Capes et al, 2008;Hobbs et al, 2003;Hosseini et al, 2010;Janhäll et al, 2010;Okoshi et al, 2014). A review of observed size-distribution data by Janhäll et al (2010) shows the differences in modal width and median diameter as a function of fuel type (forest, savannah, grass), modified combustion efficiency, and plume age (fresh versus aged). Combustion chamber experiments in the FLAME lab have demonstrated similar fuel-type differences in fresh BB size distributions .…”

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

“…The ratio between aerosol mass or number concentrations and CO has been used to trace air masses origin and age (Guyon et al, 2005;Janhäll et al, 2010). Enhancement ratios (ER BC ) for open biomass burning measured for boreal forest smoldering fires have an average ER BC of 1.7 ng m -3 ppb -1 (Kondo et al, 2011).…”