Aerosols from anthropogenic and biogenic sources and their interactions – modeling aerosol formation, optical properties, and impacts over the central Amazon basin

Abstract

Abstract. The Green Ocean Amazon experiment – GoAmazon 2014–2015 – explored the interactions between natural biogenic forest emissions from central Amazonia and urban air pollution from Manaus. Previous GoAmazon 2014–2015 studies showed that nitrogen oxide (NOx = NO + NO2) and sulfur oxide (SOx) emissions from Manaus strongly interact with biogenic volatile organic compounds (BVOCs), affecting secondary organic aerosol (SOA) formation. In previous studies, ground-based and aircraft measurements provided evidence of SOA formation and strong changes in aerosol composition and properties. Aerosol optical properties also evolve, and their impacts on the Amazonian ecosystem can be significant. As particles age, some processes, such as SOA production, black carbon (BC) deposition, particle growth and the BC lensing effect change the aerosol optical properties, affecting the solar radiation flux at the surface. This study analyzes data and models SOA formation using the Weather Research and Forecasting with Chemistry (WRF-Chem) model to assess the spatial variability in aerosol optical properties as the Manaus plumes interact with the natural atmosphere. The following aerosol optical properties are investigated: single scattering albedo (SSA), asymmetry parameter (gaer), absorption Ångström exponent (AAE) and scattering Ångström exponent (SAE). These simulations were validated using ground-based measurements at three experimental sites, namely the Amazon Tall Tower Observatory – ATTO (T0a), downtown Manaus (T1), Tiwa Hotel (T2) and Manacapuru (T3), as well as the U.S. Department of Energy (DOE) Gulfstream 1 (G-1) aircraft flights. WRF-Chem simulations were performed over 7 d during March 2014. Results show a mean biogenic SOA (BSOA) mass enrichment of 512 % at the T1 site, 450 % in regions downwind of Manaus, such as the T3 site, and 850 % in areas north of the T3 site in simulations with anthropogenic emissions. The SOA formation is rather fast, with about 80 % of the SOA mass produced in 3–4 h. Comparing the plume from simulations with and without anthropogenic emissions, SSA shows a downwind reduction of approximately 10 %, 11 % and 6 % at the T1, T2 and T3 sites, respectively. Other regions, such as those further downwind of the T3 site, are also affected. The gaer values increased from 0.62 to 0.74 at the T1 site and from 0.67 to 0.72 at the T3 site when anthropogenic emissions are active. During the Manaus plume-aging process, a plume tracking analysis shows an increase in SSA from 0.91 close to Manaus to 0.98 160 km downwind of Manaus as a result of SOA production and BC deposition.

Major Regional-Scale Production of O3 and Secondary Organic Aerosol in Remote Amazon Regions from the Dynamics and Photochemistry of Urban and Forest Emissions

“…The study area and the distribution of surrounding anthropogenic emission source and surface sites are described in detail in the study of Nascimento et al The geographical positions of the sampling stations used for the validation of the modeling in this investigation are presented in SI Appendix, Table 3. The study area with the sampling stations can be seen in the abstract graphic.…”

“…Values reach 1.0 to 1.8 μgm –3 , well above background levels. These high concentrations reach a larger area (SI Appendix, Figure S4) than previously estimated. ,− However, Palm et al estimated that some amount (0–12 μgm –3 ) of SOA could form beyond T3 using an oxidation flow reactor at the site.…”

“…The region close to Manaus (<25 km from the city center) is always VOC-limited because of high NO x emissions that sustain high NO y concentrations even during the daytime (Figure A–D). There are not enough VOCs in such areas to generate the radicals needed to convert NO to NO 2 , thus suppressing O 3 production. ,, In regions downwind of Manaus (50–200 km), the O 3 production regime varies through the day, following the dispersion of precursors and the emission of BVOCs, which depend on solar radiation and temperature …”

“…Its urban emissions make it the largest contributor of anthropogenic pollution in the Amazon basin during the wet season. , Previous studies , showed that the main contributors are light vehicles, buses, and stationary sources, such as thermal power plants and an oil refinery. This setting represents an ideal natural laboratory for investigating how anthropogenic emissions interact with biogenic compounds, modifying atmospheric chemistry and the production of ozone (O 3 ) and secondary organic aerosols (SOA). − Several studies have investigated how the transport of NO x and other anthropogenic compounds to the forest impacts the photochemical reactions that produce O 3 ,, and secondary organic aerosol (SOA). ,, The Green Ocean Amazon experiment (GoAmazon2014/5), with ground and aircraft-based measurements, has shown significant changes in aerosol composition and properties in an area up to 70 km downwind from Manaus, when compared with pristine Amazonian conditions. ,,, Experiments using an oxidation flow reactor showed that additional SOA could be produced further downwind than 70 km by the interaction between biogenic precursors, such as isoprene and formaldehyde (HCHO), and available oxidants such as O 3 and hydroxyl radicals (OH). Changes in the concentration of atmospheric oxidants can affect vegetation growth rates producing leaf injury and damage to plants. , At the same time, additional SOA could impact on Earth’s energy balance .…”

Partitioning of Organonitrates in the Production of Secondary Organic Aerosols from α-Pinene Photo-Oxidation

“…The production of organonitrates is one of the direct links for the observed effects of atmospheric NO x concentrations on SOA particle mass concentrations and yields from gaseous precursors. Even so, the link is still not well quantified or understood. , In field studies, anthropogenic NO x emissions enhanced the yield of SOA particle mass concentration from biogenic precursors in several different environments, such as in the rural environments of the Amazon forest when located downwind of pollution, , in biogenic–anthropogenic mixed air masses in western USA, and during nighttime chemistry due to monoterpene oxidation by nitrate radicals in southeastern USA . At other times, increases in NO x concentration suppressed SOA mass concentration as well as particle formation from monoterpene species oxidation − and methylglyoxal in laboratory experiments.…”