Ground- and Satellite-Based Lidar Observation of Aerosol Optical Properties Downwind of a Large Anthropogenic Pollution Source within a Tropical Rain Forest

The main goal of the GoAmazon 2014/15 experiment was to understand how aerosol and cloud life cycles are influenced by pollutant outflow from a large industrial city in a tropical rain forest, particularly the susceptibility to cloud-aerosol-precipitation interactions (Martin et al., ACP 2016). As part of the Green Ocean Amazon experiment (GoAmazon2014/5), the portable raman lidar from IPEN/SP was operated 5 km downwind of Manaus-AM/Brazil (T2 site, 3.21ºS 60.60ºW) on bank of the Amazon river. Simultaneously, the raman lidar from IF/USP measured the vertical profiles of aerosol optical properties 10 km upwind of the metropolitan area (T0e site, 2.89 ºS 59.97 ºW), thus serving as the background reference as the upwind air masses are not influenced by the urban emissions (Barbosa et al., AMT 2014).

In this study we focus on the aerosol optical properties. AERONET measurements up- and downwind of Manaus show that while the aerosol optical depth (AOD) does not change (regression coefficient of 0.98+-0.02), the absorption AOD is 2.2+-0.2 larger under the influence of the Manaus plume (Holanda, Phd thesis 2015). The backscatter and extinction coefficients obtained from the ground lidar measurements were only available during the biomass-burning season, from August 15 to October 15 2014. Periods of intense long-rang regional-scale smoke transport were excluded, and four night-time case studies were selected when the night-time river breeze allowed a boundary layer flow from T0e to T2. Backscattering and extinction coefficients were typically 10% and 50% larger, respectively, under the Manaus plume. Extinction-to-backscatter ratio was found to be about 100 sr inside the plume (similar or other urban aerosols) and 70 sr aloft (typical of biomass burning conditions). Calipso data were also used in this study. The closest downwind overpass is only 10km away, while that upwind is 15km. By averaging about 150 profiles of each type, from 2006 to 2015, we could unambiguously identify the anthropogenic plume. A comparison of Calipso and ground based instruments will be discussed as well.