Changes on aerosol properties along the transport of the Manaus city urban plume in Amazonia – results from the GoAmazon2014/5 ground-based observations

 

Authors

Luciana Rizzo — Universidade Federal de Sao Paulo
Glauber Cirino — National Institute for Amazonian Research (INPA)
Henrique de Melo Jorge Barbosa — University of Maryland, Baltimore County
Joel Brito —
Samara Carbone — University of Sao Paulo
Rodrigo Augusto Souza — Universidade do Estado do Amazonas
Scot T. Martin — Harvard University
Paulo Artaxo — University of Sao Paulo

Category

ARM field campaigns – Results from recent ARM field campaigns

Description

Amazonia is a unique place to study the impact of anthropogenic emissions on atmospheric photochemistry, and is going through localized urban development, in particular, the Manaus city in Brazil, with 2 million inhabitants. The GoAmazon2014/5 experiment (Observations and Modeling of the Green Ocean Amazon) seeks to understand the interactions between urban and biogenic emissions in Amazonia and its influence on aerosol and cloud life cycles. The experiment took place from January 2014 to December 2015. Biogenic aerosol properties were studied in 3 sampling stations upwind of Manaus (T0a, T0z and T0e). Urban impacted aerosols were analysed in two downwind sampling stations (T2 and T3). Variables monitored at ground based sites were aerosol size distribution, scattering and absorption coefficients, aerosol composition, trace gases concentrations, cloud condensation nuclei, vertical pointed X-band radars and micrometeological variables, among others. HYSPLIT backward simulations were performed, starting every 30-min during the experiment, using boundary conditions at 1o resolution from GDAS-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. The transport time from T2 to T3 was found to be 7.5 +- 1.5 h on average, considering selected trajectories inside the boundary layer. The influence of the Manaus plume on aerosol properties was more intense during the wet season, because in the dry season a significant amount of regional scale biomass burning aerosol was observed for all GoAmazon 2014/5 sites. Aerosol composition showed a dominance of organic aerosols for all sites, accounting for 65-75% of PM1 non refractory aerosol. Along the transport between the T2 and T3 sites, a significant production of secondary aerosol was observed in the urban plume, with a 40% mass increase in organics and 30% increase in sulfate aerosol mass concentration. Estimated values for the net ozone production rate within the urban plume, typically ranged between 0.8 and 3.6 ppb/h. Particle number concentration decrease by 30% on the transect between T2 and T3, while the particle mean geometric diameter increases from 45 to 55 nm, with a more pronounced accumulation mode observed at T3. At the same time, particle absorption and scattering coefficients decrease, respectively, by 50% and 30%. We will discuss the possible physical mechanisms to explain these changes.