Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

Abstract

<p><strong>Abstract.</strong> Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by one or two orders of magnitude. The measurements were made during the German-Brazilian cooperative aircraft campaign ACRIDICON-CHUVA on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September/October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. <br><br> Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the BL as a source. The air in the immediate outflow of deep convective clouds was depleted in aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5–72 hours. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. <br><br> Our findings suggest a conceptual model, where production of new aerosol particles takes place in the UT from volatile material brought up by deep convection, which is converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic carbon (BVOC) oxidation products. This may be an important source of aerosol particles in the Amazonian PBL, where aerosol nucleation and new particle formation has not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.</p>

Satellite‐Based Analysis of CO Seasonal and Interannual Variability Over the Amazon Basin

“…These climatological streamlines are derived from a reanalysis of the period from 1981 to 2010. As shown in Andreae et al (2017), similar wind patterns were found during the AC campaign in September 2014. LT winds over the Amazon Basin are strongly influenced by the Andes mountain range (Campetella & Vera, 2002).…”

Overview: Precipitation characteristics and sensitivities to environmental conditions during GoAmazon2014/5 and ACRIDICON-CHUVA

“…Therefore, the cloud droplet size distribution is different between the two regions, with forested areas producing larger cloud droplets. Figure 12 shows the cumulative histogram of the CCN concentrations (N CCN ) for the two legs over the forested and non-forested regions at approximately 1500, 1900, and 2500 m. The decrease in N CCN with altitude for boundary layer aerosols agrees with the other flights carried out during the ACRIDICON-CHUVA campaign, as shown in Andreae et al (2017). The magnitude of the N CCN is typical for polluted regions in Brazil and falls between strong biomass burning events and forested regions far away from biomass burning events.…”

“…Water droplets with a diameter ≥ 1 µm were detected by an optical particle counter. Details about the measurement mode can be found in Andreae et al (2017). The error in supersaturation resulted from the calibration uncertainty, as described by Pöhlker et al (2016); it is estimated to be in the range of 10 %.…”

Vertically resolved concentration and liquid water content of atmospheric nanoparticles at the US DOE Southern Great Plains site

“…Laakso et al (2007) also observed NPF in the mixed boundary layer and free troposphere in southern Finland using measurements on board a hot air balloon. The rapid downward mixing of small aerosol particles from the free troposphere represents an important source of aerosol particles in the pristine Amazon boundary layer (Wang et al, 2016;Andreae et al, 2017). Helicopter (Kupiszewski et al, 2013) and aircraft (Burkart et al, 2017) measurements of vertical profiles of aerosol particles in the summertime Arctic observed particle formation in the near-surface layer, with much lower concentrations at higher altitudes.…”