@Article{MorganABDFLLJHLAC:2020:TrAgBi,
author = "Morgan, William T. and Allan, James D. and Bauguitte,
St{\'e}phane and Darbyshire, Eoghan and Flynn, Michael J. and
Lee, James and Liu, Dantong and Johnson, Ben and Haywood, Jim and
Longo, Karla Maria and Artaxo, Paulo E. and Coe, Hugh",
affiliation = "{University of Manchester} and {University of Manchester} and
{Cranfield University} and {University of Manchester} and
{University of Manchester} and {University of York} and
{University of Manchester} and {Met Office} and {Met Office} and
{Instituto Nacional de Pesquisas Espaciais (INPE)} and
{Universidade de S{\~a}o Paulo (USP)} and {University of
Manchester}",
title = "Transformation and ageing of biomass burning carbonaceous aerosol
over tropical South America from aircraft in situ measurements
during SAMBBA",
journal = "Atmospheric Chemistry and Physics",
year = "2020",
volume = "20",
number = "9",
pages = "5309--5326",
month = "May",
abstract = "We present a range of airborne in situ observations of biomass
burning carbonaceous aerosol over tropical South America,
including a case study of a large tropical forest wildfire and a
series of regional survey flights across the Brazilian Amazon and
Cerrado. The study forms part of the South American Biomass
Burning Analysis (SAMBBA) project, which was conducted during
September and October 2012. We find limited evidence for net
increases in aerosol mass through atmospheric ageing combined with
substantial changes in the chemical properties of organic aerosol
(OA). Oxidation of the OA increases significantly and rapidly on
the scale of 2.5-3 h based on our case study analysis and is
consistent with secondary organic aerosol production. The
observations of limited net enhancement in OA coupled with such
changes in chemical composition imply that evaporation of OA is
also occurring to balance these changes. We observe significant
coatings on black carbon particles at source, but with limited
changes with ageing in both particle core size and coating
thickness. We quantify variability in the ratio of OA to carbon
monoxide across our study as a key parameter representing both
initial fire conditions and an indicator of net aerosol production
with atmospheric ageing. We observe ratios of 0.075-0.13 mu g
sm(-3) ppbv(-1) in the west of our study region over the Amazon
tropical forest in air masses less influenced by precipitation and
a value of 0.095 mu g sm(-3) ppbv(-1) over the Cerrado environment
in the east (where sm(-3) refers to standard metre cubed). Such
values are consistent with emission factors used by numerical
models to represent biomass burning OA emissions. Black carbon
particle core sizes typically range from mean mass diameters of
250 to 290 nm, while coating thicknesses range from 40 to 110 nm
in air masses less influenced by precipitation. The primary driver
of the variability we observe appears to be related to changes at
the initial fire source. A key lesson from our study is that
simply aggregating our observations as a function of atmospheric
ageing would have been misleading due to the complex nature of the
regional aerosol and its drivers, due to the many conflating and
competing factors that are present. Our study explores and
quantifies key uncertainties in the evolution of biomass burning
aerosol at both near-field and regional scales. Our results
suggest that the initial conditions of the fire are the primary
driver of carbonaceous aerosol physical and chemical properties
over tropical South America, aside from significant oxidation of
OA during atmospheric ageing. Such findings imply that
uncertainties in the magnitude of the aerosol burden and its
impact on weather, climate, health and natural ecosystems most
likely lie in quantifying emission sources, alongside atmospheric
dispersion, transport and removal rather than chemical
enhancements in mass.",
doi = "10.5194/acp-20-5309-2020",
url = "http://dx.doi.org/10.5194/acp-20-5309-2020",
issn = "1680-7316 and 1680-7324",
language = "en",
targetfile = "morgan_transformation.pdf",
urlaccessdate = "27 abr. 2024"
}