Carbon monoxide and related trace gases and aerosols over the Amazon Basin during the wet and dry seasons

Abstract

Abstract. We present the results of airborne measurements of carbon monoxide (CO) and aerosol particle number concentration (CN) made during the Balanço Atmosférico Regional de Carbono na Amazônia (BARCA) program. The primary goal of BARCA is to address the question of basinscale sources and sinks of CO 2 and other atmospheric carbon species, a central issue of the Large-scale BiosphereAtmosphere (LBA) program. The experiment consisted of two aircraft campaigns during November-December 2008 (BARCA-A) and May-June 2009 (BARCA-B), which covered the altitude range from the surface up to about 4500 m, and spanned most of the Amazon Basin.Based on meteorological analysis and measurements of the tracer, SF 6 , we found that airmasses over the Amazon Basin during the late dry season (BARCA-A, November 2008) originated predominantly from the Southern Hemisphere, while during the late wet season (BARCA-B, May 2009) low-level airmasses were dominated by northernhemispheric inflow and mid-tropospheric airmasses were of mixed origin. In BARCA-A we found strong influence of biomass burning emissions on the composition of the atmosphere over much of the Amazon Basin, with CO enhancements up to 300 ppb and CN concentrations approaching 10 000 cm −3 ; the highest values were in the southern part of the Basin at altitudes of 1-3 km. The CN/ CO ratios were diagnostic for biomass burning emissions, and were lower in aged than in fresh smoke. Fresh emissions indicated CO/CO 2 and CN/CO emission ratios in good agreement with previous work, but our results also highlight the need to consider the residual smoldering combustion that takes place after the active flaming phase of deforestation fires.During the late wet season, in contrast, there was little evidence for a significant presence of biomass smoke. Low CN concentrations (300-500 cm −3 ) prevailed basinwide, and CO mixing ratios were enhanced by only ∼10 ppb above the mixing line between Northern and Southern Hemisphere air. There was no detectable trend in CO with distance from the coast, but there was a small enhancement of CO in the boundary layer suggesting diffuse biogenic sources from photochemical degradation of biogenic volatile organic compounds or direct biological emission.Simulations of CO distributions during BARCA-A using a range of models yielded general agreement in spatial distribution and confirm the important contribution from biomass burning emissions, but the models evidence some systematic quantitative differences compared to observed CO concentrations. These mismatches appear to be related to problems with the accuracy of the global background fields, the role Published by Copernicus Publications on behalf of the European Geosciences Union. M. O. Andreae et al.: Carbon monoxide and related trace gases and aerosolsof vertical transport and biomass smoke injection height, the choice of model resolution, and reliability and temporal resolution of the emissions data base.

Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 2: Variability and characteristic differences under near-pristine, biomass burning, and long-range transport conditions

“…The pollution markers cCO and MBCe in Fig. 1a show a pronounced seasonal cycle with a prevalence of clean conditions in the wet season vs. the biomass burning-related pollution maximum in the dry season (Andreae et al, 2015 (Martin et al, 2010b;Andreae et al, 2012;2015). Similar to the MBCe trends, the total aerosol particle concentration NCN, 10 …”

“…), in contrast to much higher ΔNCN,10/ΔcCO levels for urban (100 -300 cm -3 ppb -1 ) and power plant emissions (up to 900 cm -3 ppb -1 ) (Janhaell et al, 2010;Kuhn et al, 2010; 15 Andreae et al, 2012). Furthermore, the ratios of excess NCCN(S) to excess cCO, ΔNCCN(S)/ΔcCO, for the individual S levels range between 6.7 ± 0.5 cm -3 ppb -1 for the lowest S = 0.11 % and values around 18.0 ± 1.3 cm -3 ppb -1 for higher S (see Table S1 and ), 'swamping' the Aitken mode DAit = 70 ± 1 nm, NAit = ~140 cm -3 ) almost completely, giving the entire distribution a monomodal appearance.…”

Modeling the radiative effects of biomass burning aerosols on carbon fluxes in the Amazon region

“…This pattern is probably related to the 20 km model resolution not picking up individual biomass burning plumes and fire emission underestimation (Pereira et al, 2016). Previous studies indicated that biomass burning emissions contribute more than 95 % to the variability of CO over the Amazon and that the emissions used in this study (3BEM; Longo et al, 2010) are about 20 % underestimated (Andreae et al, 2012).…”

“…There was an enhancement of CO from July to October for both years in all four locations. In 2010, the CO mixing ratio values in the PBL during the dry season increased from 100 to 150 ppb, which are typical wet season values (Andreae et al, 2012), to up to 500 ppb in both the simulations and observations. The dry season of 2010 had CO mixing ratios about twice as high as the same period in 2011; this is consistent with the total number of fires, which approximately doubled, detected by remote sensing during the dry season of these two years (http://www.inpe.br/queimadas/estatisticas.php).…”

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

“…4a, show a decreasing dominance of ESE winds from August to November, whereas from October to November there is an increasing influence of ENE winds, indicating the south-to-north air mass trajectory shift that occurs during the transition from the dry to the wet season. It is important to note that southerly and easterly winds are most likely to bring BB aerosol to the ATTO site during the dry season, given that very active open fire areas during this period are located in the southern Amazon and the Cerrado region (Andreae et al, 2012;Guyon et al, 2005) and, more remotely, in southern Africa (Andreae et al, 1994;Barbosa et al, 1999;Das et al, 2017). Aerosol optical depth at 550 nm is used in this study as a parameter to study the seasonal pattern of BB emission transport from both areas.…”