Evidence for anthropogenic pollution allowing for new particle formation in the Amazon boundary layer
Authors
Henrique de Melo Jorge Barbosa — University of Maryland, Baltimore County
Glauber Cirino — National Institute for Amazonian Research (INPA)
Joel Brito —
Luciana Rizzo — Universidade Federal de Sao Paulo
Samara Carbone — University of Sao Paulo
Suzane Simoes De Sa — Harvard University
Brett Palm — University of Colorado
Jose-Luis Jimenez — University of Colorado
Rodrigo Augusto Souza — Universidade do Estado do Amazonas
James Smith — University of California, Irvine
Scot T. Martin — Harvard University
Paulo Artaxo — University of Sao Paulo
Category
GoAmazon – Clouds and aerosols in Amazonia
Description
Aerosol size distributions measured at T2 and T3 during the events of downwind transport of pollution from Manaus to Manacapuru. Data is grouped by the concentration of SO2 at T2, ranging from 0 to 0.73 ppbv. Events with precipitation were excluded.
The main goal of the GoAmazon 2014/15 experiment is to measure and understand the factors affecting aerosol particles over a tropical rainforest, especially the effects of anthropogenic pollution plumes from large metropolitan areas as perturbations to the natural state of the pristine forest surrounding such areas. For helping to interpret data measured at the ground sites, we have performed HYSPLIT backward simulations, starting every 30-min from January 1 until December 31, 2014, for all the GoAmazon sites. Boundary conditions were taken every 3h at 0.5 x 0.5 deg resolution from the Global Data Assimilation System (GDAS) available from NOAA. An index for “in-plume” and “off-plume” events was built by selecting backward trajectories that started from T3 and passed over T2 / Manaus, and that had a CN/dCO ratio in the range of 41 to 130 # / ppbv (characterized from measurements at T2). We focus our analysis in the wet season to avoid having to disentangle the biomass burning transport. The transport time from T2 to T3 was found to be 4.5 +- 1.5 h on average. CN decreases by 45 # / cm3 per hour, while the mean diameter increases from 50 to 100 nm, OA mass increases by 0.7 μg / m3 per hour and SO4 increases by 30 ng / m3 per hour. By filtering the transport events by SO2 concentration at T2, we clearly identify a peak in the size distribution measured at T3, at about 30 nm, which is not present in the distribution measured at T2. The peak increases with increasing concentration of SO2, a clear indication of new particle formation. During these transport events, optical properties change as following: absorption decreases from 3.73 +- 1.18 to 1.69 +- 0.58 Mm-1, scattering decreases from 14.52 +- 4.08 to 8.53 +- 2.23 Mm-1, while the scattering angstrom exponent increases from 1.43 to 1.82. We discuss the possible physical mechanisms to explain these observations.
