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Sulfuric acid is a key contributor to new particle formation, though measurements of its gaseous concentrations are difficult to make. Several parameterizations to estimate sulfuric acid exist, all of which were constructed using measurements from the Northern Hemisphere. In this work, we report the first measurements of sulfuric acid from the Amazon Basin. These measurements are consistent with concentrations measured in Hyytiälä, Finland, though unlike Hyytiälä there is no clear correlation of sulfuric acid with global radiation. There was a minimal difference in sulfuric acid observed between the wet and dry seasons in the Amazon Basin. We also test the efficacy of existing proxies to estimate sulfuric acid in this region. Our results suggest that nighttime sulfuric acid production is due to both a stabilized Criegee intermediate pathway, and oxidation of SO2 by OH, the latter of which is not currently accounted for in existing proxies. They also illustrate the drawbacks of the common substitution of radiation for OH concentrations. None of the tested proxies effectively estimate sulfuric acid measurements at night. For estimates at all times of day, a recently published proxy based on data from the boreal forest should be used. If only daytime estimates are needed, several recent proxies that do not include the Criegee pathway are sufficient. More investigation of nighttime sulfuric acid production pathways is necessary to close the gap between measurements and estimates with existing proxies. [ABSTRACT FROM AUTHOR]

The Green Ocean Amazon experiment - GoAmazon2014/5 explored the interactions between natural biogenic forest emissions from Central Amazonia and urban air pollution from Manaus. Previous GoAmazon2014/5 studies showed that nitrogen oxides (NOx = NO + NO2) and sulfur oxides (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 of 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: Amazon Tall Tower Observatory - ATTO (T0a), downtown Manaus (T1), Tiwa Hotel (T2) and Manacapuru (T3), as well as the G1 aircraft flights. WRF-Chem simulations were performed over seven days 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 hours. 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. 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. [ABSTRACT FROM AUTHOR]

In the period between July 9th and 11th, 2014 a Friagem event reached the central Amazon region causing significant changes in microclimate and atmospheric chemistry. On July 11th, the southwest flow related to the Friagem converged with the easterly winds in the central Amazon region. The interaction between these two distinct air masses formed a convection band, which intensified over the Manaus region and the Amazon Tall Tower Observatory (ATTO) site. The satellite images show the evolution of convective activity on July 11th, which lead to 21 mm of precipitation in the ATTO site. Moreover, the arrival of the Friagem caused a sudden drop in temperature and a predominance of southerly winds, which could be seen in Porto Velho between July 7th and 8th and in Manaus and ATTO site from July 9th to 11th. The results of ERA-Interim reanalysis and Brazilian developments on the Regional Atmospheric Modeling System (BRAMS) simulations show that this Friagem event coming from the southwest, carries a mass of air with higher O3 and NO2 mixing ratios and lower CO mixing ratio compared to the airmasses present at the central Amazon. At lake Balbina the Friagem intensifies the local circulations, such as the breeze phenomena. At the Manaus region and ATTO site, the main effects of the Friagem event are: a decrease in the incoming solar radiation (due to intense cloud formation), a large temperature drop and a distinct change in surface O3 and CO2 mixing ratios. As the cold air of the Friagem was just in the lower 500 m the most probable cause of this change is that a cold pool above the forest prevented vertical mixing causing accumulation of CO2 from respiration and very low O3 mixing ratio due to photochemistry reduction and limited mixing within the boundary layer. [ABSTRACT FROM AUTHOR]

In this study, aerosol samples collected at a remote site in the Amazonian rainforest and an urban site in Manaus, Brazil, were investigated on a single particle basis using a quantitative energy-dispersive electron probe X-ray microanalysis (ED-EPMA). Twenty-three aerosol samples were collected in four size ranges (0.25-0.5, 0.5-1.0, 1.0-2.0, and 2.0-4.0 µm) during the wet season in 2012 at two Amazon basin sites: 10 samples in Manaus, an urban area; and 13 samples at an 80-m high tower, located at the Amazon Tall Tower Observatory (ATTO) site in the middle of the rainforest, 150 km northeast of Manaus. The aerosol particles were classified into nine particle types based on the morphology on the secondary electron images (SEIs) together with the elemental concentrations of 3,162 individual particles: (i) secondary organic aerosols (SOA), (ii) ammonium sulfate (AS), (iii) SOA and AS mixtures, (iv) aged mineral dust, (v) reacted sea-salts, (vi) primary biological aerosol (PBA), (vii) carbon-rich or elemental carbon (EC) particles, such as soot, tar ball, and char, (viii) fly ash, and (ix) heavy metal (HM, such as Fe, Zn, Ni, and Ti)-containing particles. In submicron aerosols collected at the ATTO site, SOA and AS mixture particles were predominant (50-94 % in relative abundance) with SOA and ammonium sulfate comprising 73-100 %. In supermicron aerosols at the ATTO site, aged mineral dust and sea-salts (37-70 %) as well as SOA and ammonium sulfate (28-58 %) were abundant. PBAs were observed abundantly in the PM2-4 fraction (46 %), and EC and fly ash particles were absent in all size fractions. The analysis of a bulk PM0.25-0.5 aerosol sample from the ATTO site using Raman microspectrometry and attenuated total reflection Fourier transform infrared spectroscopy showed that ammonium sulfate, organics, and minerals are the major chemical species, which is consistent with the ED-EPMA results. In the submicron aerosols collected in Manaus, either SOA and ammonium sulfate (17-80 %) or EC particles (6-78 %) were dominant depending on the samples. In contrast, aged mineral dust, reacted sea-salt, PBA, SOA, ammonium sulfate, and EC particles comprised most of the supermicron aerosols collected in Manaus. The SOA, ammonium sulfate, and PBAs were mostly of a biogenic origin from the rainforest, whereas the EC and HM-containing particles were of an anthropogenic origin. Aged mineral dust and reacted sea-salt particles, including mineral dust mixed with sea-salts probably during long-range transatlantic transport, were abundant in the supermicron fractions at both sites. Among the aged mineral dust and reacted sea-salt particles, sulfate-containing ones outnumbered those containing nitrates and sulfate+nitrate in the ATTO samples. In contrast, particles containing sulfate+nitrate were comparable in number to particles containing sulfate only in the Manaus samples, indicating the different sources and formation mechanisms of secondary aerosols, i.e., the predominant presence of sulfate at the ATTO site from mostly biogenic emissions and the elevated influences of nitrates from anthropogenic activities at the Manaus site. [ABSTRACT FROM AUTHOR]

The effect of river breezes on pollutant plume dispersion or canalization in the central Amazon was evaluated. A pollution plume changes atmospheric composition downwind of Manaus, a city of 2 million people positioned at the confluence between two wide rivers. Herein, to evaluate the effects of river breezes, two cases were modeled at the mesoscale for March 2014. The first case, "with rivers" (wR), simulated the transport and chemistry of the Manaus pollution plume as the rivers were in reality. The second case, "without rivers" (woR), carried out simulations for which all rivers and floodable areas were replaced by forest. The three main conclusions are as follows: (1) Between the two cases, alterations in wind speeds were maximum at local noon, and river breezes influenced horizontal wind fields from surface up to 150 m in altitude, suggesting a capping height of 150 m on most days for the influence of river breezes on pollutant concentrations. In agreement with this modeling result, data sets collected at 500 m by aircraft flights showed no apparent influence of the underlying rivers on plume dispersion. The flights traversed the plume downwind of Manaus during the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) Experiment. (2) Between the wR and wOR cases, changes to downwind concentrations of O3, NOx, and CO pollutants were < 6 % as a monthly average at the supersite "T3" of GoAmazon2014/5, which was 70 km downwind of Manaus and located between the two main rivers. As single events at T3, maximum one-hour concentration differences were 39 ppb for O3, 5 ppb for NOx, and 26 ppb for CO. (3) For a focus on the surface layer of the rivers (0 to 150 m in height), river breezes increased the monthly average O3, NOx, and CO surface concentrations by 25 %, 25 %, and < 5 %, respectively. In addition, strong canalization occurred 5 % of the time based on a difference of 10 ppb in the surface concentrations of at least two of O3, NOx, and CO between the wR and wOR cases. In conclusion, although pollutants dispersed by river breezes could at times be a strong effect on observed pollutant concentrations in the surface river boundary layer, overall most pollution was transported at heights well above the effects of the river breezes and moved downwind along the trajectories of the dominant trade winds. [ABSTRACT FROM AUTHOR]

This paper evaluates the impact of the emissions from mobile and stationary sources in the Amazon rainforest by using the Weather Research and Forecasting with Chemistry (WRF-Chem) model. The analyzed air pollutants were CO, NOx, SO2, O3, PM2.5, PM10 and VOCs. Five scenarios were defined in order to evaluate the emissions by biogenic, mobile and stationary sources, as well as future scenarios. Results show that the stationary sources explain the highest concentrations for all air pollutants evaluated, except for CO, for which the mobile sources are predominant ones. The futuristic scenario, which is twice the current emissions from mobile and stationary sources, has shown an increase in the range of 3 to 62 % in average concentrations and 45 to 109 % in peak concentrations depending on the pollutant. In addition, the spatial distributions of the scenarios has shown that the air pollutions plume from the city of Manaus is predominantly west and southwest, and it can reach hundreds of kilometers in length. [ABSTRACT FROM AUTHOR]

How a changing energy matrix for power production affects air quality is considered for an urban region in a tropical, forested environment. Manaus, the largest city in the central Amazon basin of Brazil, is in the process of changing its fossil fuel power energy matrix from entirely fuel oil and diesel to nearly entirely natural gas across an approximately ten-year period. Three scenarios of urban air quality, specifically afternoon ozone concentrations, were simulated using the Weather Research and Forecasting (WRF-Chem) model. The first scenario used fuel oil and diesel for power production, which was the reality in 2008. The second scenario was based on the fuel mix from 2014, the most current year for which data were available. The third scenario considered nearly complete use of natural gas for power production, which is the anticipated future, possibly for 2018. For each case, inventories of anthropogenic emissions were based on power generation, refining operations, and transportation. Transportation and refinery operations were held constant across the three scenarios to focus on effects of power plant fuel switching in a tropical context. The results of the simulations indicate that a change to natural gas significantly decreases maximum afternoon ozone concentrations over the population center, reaching reductions of 73 % (110 to 30 ppb) on the most polluted days. NOx and CO emissions decreased by approximately 89 % and 55 %, respectively, after the complete change in the energy matrix. The sensitivity of ozone concentrations to the fuel switchover is consistent with a NOx-limited regime, as expected for a tropical forest having high emissions of biogenic volatile organic compounds, high water vapor concentrations, and abundant solar radiation. Thus, policies favoring the burning of natural gas in place of fuel oil and diesel have great potential for ozone reduction and improve air quality for growing urban regions located in tropical, forested environments around the world. [ABSTRACT FROM AUTHOR]

The intercontinental transport of aerosols from the Sahara is likely to play a significant role in nutrient cycles in the Amazon rainforest, since it carries many types of minerals to these otherwise low-fertility lands. Iron is one of the micronutrients essential for plant growth, and the Amazon rainforest is iron-limited. The main aim of this study was to assess the input and potential impact of iron bioavailability from Saharan dust, namely, the soluble fraction Fe(II)/Fe(III). Seven other soluble elements that are also essential for plants were measured. Dust particles entrained in the air were collected and analyzed, but not dust deposited in rainfall as atmospheric washout. The sampling campaign was carried out at the ATTO site (Amazon Tall Tower Observatory), from March to April 2015, and samplers were placed both above and below the canopy. Mineral dust aerosol at ATTO showed peak concentrations for Fe(III) (47.6 ng m−3), Fe(II) (16.2 ng m−3), Na (470 ng m−3), Ca (194 ng m−3), K (64.7 ng m−3), and Mg (88.8 ng m−3) during the presence of dust transported from the Sahara, as determined by remote ground-based and satellite sensing data and backward trajectories. Atmospheric transport of weathered Saharan dust, followed by surface deposition, results in substantial iron bioavailability across the rainforest canopy. The seasonal deposition of dust rich in soluble iron and other minerals is likely to affect both bacteria and fungi within the topsoil and on canopy surfaces, and especially benefit highly bioabsorbent epiphytes, such as lichens. In this scenario, Saharan dust can provide essential macronutrients and micronutrients to plant roots, and also directly to plant leaves. The influence on the ecology of the forest canopy and topsoil would likely be different from that of nutrients from the weathered Amazon bedrock, which provides the main source of soluble mineral nutrients. [ABSTRACT FROM AUTHOR]