Urban influence on the concentration and composition of submicron particulate matter in central Amazonia
Authors: de Sá Suzane S. , Palm Brett B. , Campuzano-Jost Pedro , Day Douglas A. , Hu Weiwei , Isaacman-VanWertz Gabriel , Yee Lindsay D. , Brito Joel , Carbone Samara , Ribeiro Igor O. , Cirino Glauber G. , Liu Yingjun , Thalman Ryan , Sedlacek Arthur , Funk Aaron , Schumacher Courtney , Shilling John E. , Schneider Johannes , Artaxo Paulo , Goldstein Allen H. , Souza Rodrigo A. F. , Wang Jian , McKinney Karena A. , Barbosa Henrique , Alexander M. Lizabeth , Jimenez Jose L. , Martin Scot T. 
Published: August 2018

Abstract. An understanding of how anthropogenic emissions
affect the concentrations and composition of airborne particulate matter
(PM) is fundamental to quantifying the influence of human activities
on climate and air quality. The central Amazon Basin, especially around the city of Manaus, Brazil,
has experienced rapid changes in the past decades due to ongoing
urbanization. Herein, changes in the concentration and composition of
submicron PM due to pollution downwind of the Manaus metropolitan region are
reported as part of the GoAmazon2014/5 experiment. A high-resolution
time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a suite of other
gas- and particle-phase instruments were deployed at the “T3” research
site, 70 km downwind of Manaus, during the wet season. At this site, organic
components represented 79±7 % of the non-refractory
PM1 mass concentration on average, which was in the same range as several upwind
sites. However, the organic PM1 was considerably more oxidized at T3
compared to upwind measurements. Positive-matrix factorization (PMF) was
applied to the time series of organic mass spectra collected at the T3 site,
yielding three factors representing secondary processes (73±15 % of
total organic mass concentration) and three factors representing primary
anthropogenic emissions (27±15 %). Fuzzy c-means clustering (FCM)
was applied to the afternoon time series of concentrations of NOy,
ozone, total particle number, black carbon, and sulfate. Four clusters were
identified and characterized by distinct air mass origins and particle
compositions. Two clusters, Bkgd-1 and Bkgd-2, were associated with
background conditions. Bkgd-1 appeared to represent near-field atmospheric PM
production and oxidation of a day or less. Bkgd-2 appeared to represent
material transported and oxidized for two or more days, often with
out-of-basin contributions. Two other clusters, Pol-1 and Pol-2, represented
the Manaus influence, one apparently associated with the northern region of
Manaus and the other with the southern region of the city. A composite of the
PMF and FCM analyses provided insights into the anthropogenic effects on PM
concentration and composition. The increase in mass concentration of
submicron PM ranged from 25 % to 200 % under polluted compared with
background conditions, including contributions from both primary and
secondary PM. Furthermore, a comparison of PMF factor loadings for different
clusters suggested a shift in the pathways of PM production under polluted
conditions. Nitrogen oxides may have played a critical role in these shifts.
Increased concentrations of nitrogen oxides can shift pathways of PM
production from HO2-dominant to NO-dominant as well as increase the
concentrations of oxidants in the atmosphere. Consequently, the oxidation of
biogenic and anthropogenic precursor gases as well as the oxidative
processing of preexisting atmospheric PM can be accelerated. This combined
set of results demonstrates the susceptibility of atmospheric chemistry, air
quality, and associated climate forcing to anthropogenic perturbations over
tropical forests.