Evaluation of the carbon content of aerosols from the burning of biomass in the Brazilian Amazon using thermal, optical and thermal-optical analysis methods

Abstract

Abstract. Aerosol samples were collected at a pasture site in the Amazon Basin as part of the project LBA-SMOCC-2002 (Large-Scale Biosphere-Atmosphere Experiment in Amazonia -Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate). Sampling was conducted during the late dry season, when the aerosol composition was dominated by biomass burning emissions, especially in the submicron fraction. A 13-stage Dekati low-pressure impactor (DLPI) was used to collect particles with nominal aerodynamic diameters (D p ) ranging from 0.03 to 0.10 µm. Gravimetric analyses of the DLPI substrates and filters were performed to obtain aerosol mass concentrations. The concentrations of total, apparent elemental, and organic carbon (TC, EC a , and OC) were determined using thermal and thermal-optical analysis (TOA) methods. A light transmission method (LTM) was used to determine the concentration of equivalent black carbon (BC e ) or the absorbing fraction at 880 nm for the size-resolved samples.During the dry period, due to the pervasive presence of fires in the region upwind of the sampling site, concentrations of fine aerosols (D p < 2.5µm: average 59.8 µg m −3 ) were higher than coarse aerosols (D p > 2.5µm: 4.1 µg m −3 ). Carbonaceous matter, estimated as the sum of the particulate organic matter (i.e., OC × 1.8) plus BC e , comprisedCorrespondence to: O. L. Mayol-Bracero (omayol@ites.upr.edu) more than 90% to the total aerosol mass. Concentrations of EC a (estimated by thermal analysis with a correction for charring) and BC e (estimated by LTM) averaged 5.2 ± 1.3 and 3.1 ± 0.8 µg m −3 , respectively. The determination of EC was improved by extracting water-soluble organic material from the samples, which reduced the average light absorptionÅngström exponent of particles in the size range of 0.1 to 1.0 µm from >2.0 to approximately 1.2. The size-resolved BC e measured by the LTM showed a clear maximum between 0.4 and 0.6 µm in diameter. The concentrations of OC and BC e varied diurnally during the dry period, and this variation is related to diurnal changes in boundary layer thickness and in fire frequency.

Free troposphere as a major source of CCN for the equatorial pacific boundary layer: long-range transport and teleconnections

“…Over half of it is volatile upon heating to 360 • C and largely water soluble (Soto-García et al, 2011). Even greater OC fractions were observed in the wet season (Gunthe et al, 2009) and both periods reveal a larger OC fraction (up to 90 %) in the Aitken size range.…”

“…The relative impact on boundary layer CCN in this distant region will depend upon the precursors that are available to influence growth to CCN sizes and/or what other aerosol and CCN are already present at this location (e.g., combustion aerosol). The mean FT size distribution above the inversion for higher CO has a mode diameter of about a factor of 2 smaller (about an order of magnitude less mass per particle) than observed in combustion outflow near SA using these same instruments (Moore II et al, 2003) and far smaller than sizes reported for Amazon biomass burning at the surface (Rissler et al, 2006;Soto-García et al, 2011). However, deep convection over the Amazon has been found to loft aerosol to 10 km while scavenging about 90 % of the accumulation mode before advection out over the Pacific (Andreae et al, 2001).…”

Optimized method for black carbon analysis in ice and snow using the Single Particle Soot Photometer

“…We run the broadband and narrowband detectors with staggered gains and combine the signals from the high-gain broadband output with the low-gain narrowband output in order to maximize the detectable BC mass (per particle) range. The band ratio, calculated from the ratio of the broadband to narrowband signals, depends on the boiling-point temperature and the spectral emissivity of the incandescent material, thus providing information to distinguish BC particles from, e.g., metal particles (Stephens et al, 2003). The calibration of the SP2 was conducted up to a mass of 70 fg BC.…”

“…Ice cores offer a unique medium to study the variability of BC concentrations over long time periods, but analyses that require large sample volumes result in low time (or depth) resolution. Furthermore, the filter-based methods have the potential to over-or underestimate the BC mass concentration due to analytical artifacts, such as charring of organic carbon (Soto-García et al, 2011), dust interference (Wang et al, 2012) or filter efficiency (Torres et al, 2014).…”

Refractory Black carbon (rBC) variability in a 47-year West Antarctic Snow and Firn core

“…BC has been studied in Antarctic snow since the late 1980s and early 1990s (Chýlek et al, 1987(Chýlek et al, , 1992Warren and Clarke, 1990). These initial studies used filter-based methods, which could under-or overestimate BC concentrations due to some analytical artifacts (Soto-García et al, 2011;Torres et al, 2014;Wang et al, 2012). Studies using the SP2 started appearing more than two decades later, aiming at recent snow rBC concentrations (Casey et al, 2017;Khan et al, 2019), near-surface air (Khan et al, 2018), recent-past ice cores (couple centuries - Bisiaux et al, 2012aBisiaux et al, , 2012b and the past millennia (Arienzo et al, 2017).…”