The Sao Paulo Metropolitan Area is a unique case worldwide due to the extensive use of biofuel, particularly ethanol, by its large fleet of nearly 8 million cars. Based on source apportionment ...analysis of Organic Aerosols in downtown Sao Paulo, and using ethanol as tracer of passenger vehicles, we have identified primary emissions from light-duty-vehicles (LDV) and heavy-duty-vehicles (HDV), as well as secondary process component. Each of those factors mirror a relevant primary source or secondary process in this densely occupied area. Using those factors as predictors in a multiple linear regression analysis of a wide range of pollutants, we have quantified the role of primary LDV or HDV emissions, as well as atmospheric secondary processes, on air quality degradation. Results show a significant contribution of HDV emissions, despite contributing only about 5% of vehicles number in the region. The latter is responsible, for example, of 40% and 47% of benzene and black carbon atmospheric concentration, respectively. This work describes an innovative use of biofuel as a tracer of passenger vehicle emissions, allowing to better understand the role of vehicular sources on air quality degradation in one of most populated megacities worldwide.
Soils are a major source of nitrogen oxides, which in the atmosphere help govern its oxidative capacity. Thus the response of soil nitric oxide (NO) emissions to forcings such as warming or forest ...loss has a meaningful impact on global atmospheric chemistry. We find that the soil emission rate of NO in Amazonia from a common inventory is biased low by at least an order of magnitude in comparison to tower‐based observations. Accounting for this regional bias decreases the modeled global methane lifetime by 1.4%–2.6%. In comparison, a fully deforested Amazonia, representing a 37% decrease in global emissions of isoprene, decreases methane lifetime by at most 4.6%, highlighting the sensitive response of oxidation rates to changes in emissions of NO compared to those of terpenes. Our results demonstrate that improving our understanding of soil NO emissions will yield a more accurate representation of atmospheric oxidative capacity.
Plain Language Summary
Soils emit a gas called nitric oxide (NO). The amount of NO emitted from soils in tropical forests is not well known, but has been assumed to be small. We simulated how different amounts of NO emissions from soils in the Amazon impacted atmospheric chemistry. By comparing our modeled results to observations we found that NO emissions from soils in the Amazon may be between 10 and 20 times larger than the current default assumption. This matters because NO has a strong influence on the rate at which methane and other gasses are removed from the atmosphere. Therefore soil NO emissions end up impacting how long methane can last in the atmosphere, and that would have additional climate impacts. Even though soil NO emissions are smaller than other sources of NO emissions globally, we find that the amount of NO emitted in the Amazon matters a lot for how long methane can last in the atmosphere. Our results demonstrate that improving estimates of soil NO emissions is going to be necessary for making accurate estimates of how long methane and other reactive species will stay in the atmosphere.
Key Points
Soil emission rates of NO in common inventories may be between 10× and 20× too low over the Amazon basin
Higher soil NO over the Amazon basin alters the oxidative capacity of the atmosphere and decreases global methane lifetime by 1.4%–2.6%
Global methane lifetime is more sensitive to Amazon soil NO fluxes than to the loss of terpene fluxes from total deforestation of the Amazon
In the Amazon basin, particles containing mixed sodium salts are routinely observed and are attributed to marine aerosols transported from the Atlantic Ocean. Using chemical imaging analysis, we show ...that, during the wet season, fungal spores emitted by the forest biosphere contribute at least 30% (by number) to sodium salt particles in the central Amazon basin. Hydration experiments indicate that sodium content in fungal spores governs their growth factors. Modeling results suggest that fungal spores account for ~69% (31-95%) of the total sodium mass during the wet season and that their fractional contribution increases during nighttime. Contrary to common assumptions that sodium-containing aerosols originate primarily from marine sources, our results suggest that locally-emitted fungal spores contribute substantially to the number and mass of coarse particles containing sodium. Hence, their role in cloud formation and contribution to salt cycles and the terrestrial ecosystem in the Amazon basin warrant further consideration.
The Amazon rainforest is a sensitive ecosystem experiencing the combined pressures of progressing deforestation and climate change. Its atmospheric conditions oscillate between biogenic and biomass ...burning (BB) dominated states. The Amazon further represents one of the few remaining continental places where the atmosphere approaches pristine conditions during occasional wet season episodes. The Amazon Tall Tower Observatory (ATTO) has been established in central Amazonia to investigate the complex interactions between the rainforest ecosystem and the atmosphere. Physical and chemical aerosol properties have been analyzed continuously since 2012. This paper provides an in-depth analysis of the aerosol's optical properties at ATTO based on data from 2012 to 2017. The following key results have been obtained. The aerosol scattering and absorption coefficients at 637 nm, σsp,637 and σap,637, show a pronounced seasonality with lowest values in the clean wet season (mean ± SD: σsp,637=7.5±9.3 M m−1; σap,637=0.68±0.91 M m−1) and highest values in the BB-polluted dry season (σsp,637=33±25 M m−1; σap,637=4.0±2.2 M m−1). The single scattering albedo at 637 nm, ω0, is lowest during the dry season (ω0=0.87±0.03) and highest during the wet season (ω0=0.93±0.04). The retrieved BC mass absorption cross sections, αabs, are substantially higher than values widely used in the literature (i.e., 6.6 m2 g−1 at 637 nm wavelength), likely related to thick organic or inorganic coatings on the BC cores. Wet season values of αabs=11.4±1.2 m2 g−1 (637 nm) and dry season values of αabs=12.3±1.3 m2 g−1 (637 nm) were obtained. The BB aerosol during the dry season is a mixture of rather fresh smoke from local fires, somewhat aged smoke from regional fires, and strongly aged smoke from African fires. The African influence appears to be substantial, with its maximum from August to October. The interplay of African vs. South American BB emissions determines the aerosol optical properties (e.g., the fractions of black vs. brown carbon, BC vs. BrC). By analyzing the diel cycles, it was found that particles from elevated aerosol-rich layers are mixed down to the canopy level in the early morning and particle number concentrations decrease towards the end of the day. Brown carbon absorption at 370 nm, σap,BrC,370, was found to decrease earlier in the day, likely due to photo-oxidative processes. BC-to-CO enhancement ratios, ERBC, reflect the variability of burnt fuels, combustion phases, and atmospheric removal processes. A wide range of ERBC between 4 and 15 ng m−3 ppb−1 was observed with higher values during the dry season, corresponding to the lowest ω0 levels (0.86–0.93). The influence of the 2009/2010 and 2015/2016 El Niño periods and the associated increased fire activity on aerosol optical properties was analyzed by means of 9-year σsp and σap time series (combination of ATTO and ZF2 data). Significant El Niño-related enhancements were observed: in the dry season, σsp,637 increased from 24±18 to 48±33 M m−1 and σap, 637 from 3.8±2.8 to 5.3±2.5 M m−1. The absorption Ångström exponent, åabs, representing the aerosol absorption wavelength dependence, was mostly <1.0 with episodic increases upon smoke advection. A parameterization of åabs as a function of the BC-to-OA mass ratio for Amazonian aerosol ambient measurements is presented. The brown carbon (BrC) contribution to σap at 370 nm was obtained by calculating the theoretical BC åabs, resulting in BrC contributions of 17 %–29 % (25th and 75th percentiles) to σap 370 for the entire measurement period. The BrC contribution increased to 27 %–47 % during fire events under El Niño-related drought conditions from September to November 2015. The results presented here may serve as a basis to understand Amazonian atmospheric aerosols in terms of their interactions with solar radiation and the physical and chemical-aging processes that they undergo during transport. Additionally, the analyzed aerosol properties during the last two El Niño periods in 2009/2010 and 2015/2016 offer insights that could help to assess the climate change-related potential for forest-dieback feedbacks under warmer and drier conditions.
We use the GLOMAP global aerosol model evaluated against observations of surface particulate matter (PM2.5) and aerosol optical depth (AOD) to better understand the impacts of biomass burning on ...tropical aerosol over the period 2003 to 2011. Previous studies report a large underestimation of AOD over regions impacted by tropical biomass burning, scaling particulate emissions from fire by up to a factor of 6 to enable the models to simulate observed AOD. To explore the uncertainty in emissions we use three satellite-derived fire emission datasets (GFED3, GFAS1 and FINN1). In these datasets the tropics account for 66–84 % of global particulate emissions from fire. With all emission datasets GLOMAP underestimates dry season PM2.5 concentrations in regions of high fire activity in South America and underestimates AOD over South America, Africa and Southeast Asia. When we assume an upper estimate of aerosol hygroscopicity, underestimation of AOD over tropical regions impacted by biomass burning is reduced relative to previous studies. Where coincident observations of surface PM2.5 and AOD are available we find a greater model underestimation of AOD than PM2.5, even when we assume an upper estimate of aerosol hygroscopicity. Increasing particulate emissions to improve simulation of AOD can therefore lead to overestimation of surface PM2.5 concentrations. We find that scaling FINN1 emissions by a factor of 1.5 prevents underestimation of AOD and surface PM2.5 in most tropical locations except Africa. GFAS1 requires emission scaling factor of 3.4 in most locations with the exception of equatorial Asia where a scaling factor of 1.5 is adequate. Scaling GFED3 emissions by a factor of 1.5 is sufficient in active deforestation regions of South America and equatorial Asia, but a larger scaling factor is required elsewhere. The model with GFED3 emissions poorly simulates observed seasonal variability in surface PM2.5 and AOD in regions where small fires dominate, providing independent evidence that GFED3 underestimates particulate emissions from small fires. Seasonal variability in both PM2.5 and AOD is better simulated by the model using FINN1 emissions. Detailed observations of aerosol properties over biomass burning regions are required to better constrain particulate emissions from fires.
Fire and deforestation dynamics in Amazonia (1973–2014) Marle, Margreet J. E.; Field, Robert D.; Werf, Guido R. ...
Global biogeochemical cycles,
January 2017, 2017-01-00, 20170101, Letnik:
31, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Consistent long‐term estimates of fire emissions are important to understand the changing role of fire in the global carbon cycle and to assess the relative importance of humans and climate in ...shaping fire regimes. However, there is limited information on fire emissions from before the satellite era. We show that in the Amazon region, including the Arc of Deforestation and Bolivia, visibility observations derived from weather stations could explain 61% of the variability in satellite‐based estimates of bottom‐up fire emissions since 1997 and 42% of the variability in satellite‐based estimates of total column carbon monoxide concentrations since 2001. This enabled us to reconstruct the fire history of this region since 1973 when visibility information became available. Our estimates indicate that until 1987 relatively few fires occurred in this region and that fire emissions increased rapidly over the 1990s. We found that this pattern agreed reasonably well with forest loss data sets, indicating that although natural fires may occur here, deforestation and degradation were the main cause of fires. Compared to fire emissions estimates based on Food and Agricultural Organization's Global Forest and Resources Assessment data, our estimates were substantially lower up to the 1990s, after which they were more in line. These visibility‐based fire emissions data set can help constrain dynamic global vegetation models and atmospheric models with a better representation of the complex fire regime in this region.
Key Points
Visibility data can be used as proxy for annual fire emissions in the Amazon
Fire emissions here were low up to the late 1980s and increased afterwards with substantial interannual variability
Fire‐driven deforestation in the 1970s and 1980s was lower than found in other data sets
In the wet season, a large portion of the Amazon region constitutes one of the most pristine continental areas, with very low concentrations of atmospheric trace gases and aerosol particles. However, ...land use change modifies the biosphere-atmosphere interactions in such a way that key processes that maintain the functioning of Amazonia are substantially altered. This study presents a comparison between aerosol properties observed at a preserved forest site in Central Amazonia (TT34 North of Manaus) and at a heavily biomass burning impacted site in south-western Amazonia (PVH, close to Porto Velho). Amazonian aerosols were characterized in detail, including aerosol size distributions, aerosol light absorption and scattering, optical depth and aerosol inorganic and organic composition, among other properties. The central Amazonia site (TT34) showed low aerosol concentrations (PM2.5 of 1.3 +/- 0.7 microg m(-3) and 3.4 +/- 2.0 microg m(-3) in the wet and dry seasons, respectively), with a median particle number concentration of 220 cm(-3) in the wet season and 2200 cm(-3) in the dry season. At the impacted site (PVH), aerosol loadings were one order of magnitude higher (PM2.5 of 10.2 +/- 9.0 microg m(-3) and 33.0 +/- 36.0 microg m(-3) in the wet and dry seasons, respectively). The aerosol number concentration at the impacted site ranged from 680 cm(-3) in the wet season up to 20 000 cm(-3) in the dry season. An aerosol chemical speciation monitor (ACSM) was deployed in 2013 at both sites, and it shows that organic aerosol account to 81% to the non-refractory PM1 aerosol loading at TT34, while biomass burning aerosols at PVH shows a 93% content of organic particles. Three years of filter-based elemental composition measurements shows that sulphate at the impacted site decreases, on average, from 12% of PM2.5 mass during the wet season to 5% in the dry season. This result corroborates the ACSM finding that the biomass burning contributed overwhelmingly to the organic fine mode aerosol during the dry season in this region. Aerosol light scattering and absorption coefficients at the TT34 site were low during the wet season, increasing by a factor of 5, approximately, in the dry season due to long range transport of biomass burning aerosols reaching the forest site in the dry season. Aerosol single scattering albedo (SSA) ranged from 0.84 in the wet season up to 0.91 in the dry. At the PVH site, aerosol scattering coefficients were 3-5 times higher in comparison to the TT34 site, an indication of strong regional background pollution, even in the wet season. Aerosol absorption coefficients at PVH were about 1.4 times higher than at the forest site. Ground-based SSA at PVH was around 0.92 year round, showing the dominance of scattering aerosol particles over absorption, even for biomass burning aerosols. Remote sensing observations from six AERONET sites and from MODIS since 1999, provide a regional and temporal overview. Aerosol Optical Depth (AOD) at 550 nm of less than 0.1 is characteristic of natural conditions over Amazonia. At the perturbed PVH site, AOD550 values greater than 4 were frequently observed in the dry season. Combined analysis of MODIS and CERES showed that the mean direct radiative forcing of aerosols at the top of the atmosphere (TOA) during the biomass burning season was -5.6 +/- 1.7 W m(-2), averaged over whole Amazon Basin. For high AOD (larger than 1) the maximum daily direct aerosol radiative forcing at the TOA was as high as -20 W m(-2) locally. This change in the radiation balance caused increases in the diffuse radiation flux, with an increase of Net Ecosystem Exchange (NEE) of 18-29% for high AOD. From this analysis, it is clear that land use change in Amazonia shows alterations of many atmospheric properties, and these changes are affecting the functioning of the Amazonian ecosystem in significant ways.
The intercontinental transport of aerosols from the Sahara desert plays 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 its long-range transport might be an important source for the iron-limited Amazon rainforest. This study assesses the bioavailability of iron Fe(II) and Fe(III) in the particulate matter over the Amazon forest, which was transported from the Sahara desert (for the sake of our discussion, this term also includes the Sahel region). The sampling campaign was carried out above and below the forest canopy at the ATTO site (Amazon Tall Tower Observatory), a near-pristine area in the central Amazon Basin, from March to April 2015. Measurements reached peak concentrations for soluble Fe(III) (48 ng m−3), Fe(II) (16 ng m−3), Na (470 ng m−3), Ca (194 ng m−3), K (65 ng m−3), and Mg (89 ng m−3) during a time period of dust transport from the Sahara, as confirmed by ground-based and satellite remote sensing data and air mass backward trajectories. Dust sampled above the Amazon canopy included primary biological aerosols and other coarse particles up to 12 µm in diameter. Atmospheric transport of weathered Saharan dust, followed by surface deposition, resulted in substantial iron bioavailability across the rainforest canopy. The seasonal deposition of dust, rich in soluble iron, and other minerals is likely to assist both bacteria and fungi within the topsoil and on canopy surfaces, and especially benefit highly bioabsorbent species. In this scenario, Saharan dust can provide essential macronutrients and micronutrients to plant roots, and also directly to plant leaves. The influence of this input on the ecology of the forest canopy and topsoil is discussed, and we argue that this influence would likely be different from that of nutrients from the weathered Amazon bedrock, which otherwise provides the main source of soluble mineral nutrients.
Urbanization and deforestation have important impacts on atmospheric
particulate matter (PM) over Amazonia. This study presents observations and
analysis of PM1 concentration, composition, and ...optical
properties in central Amazonia during the dry season, focusing on the
anthropogenic impacts. The primary study site was located 70 km downwind of
Manaus, a city of over 2 million people in Brazil, as part of the
GoAmazon2014/5 experiment. A high-resolution time-of-flight aerosol mass
spectrometer (AMS) provided data on PM1 composition, and aethalometer
measurements were used to derive the absorption coefficient babs,BrC of
brown carbon (BrC) at 370 nm. Non-refractory PM1 mass concentrations
averaged 12.2 µg m−3 at the primary study site, dominated by
organics (83 %), followed by sulfate (11 %). A decrease in
babs,BrC was observed as the mass concentration of nitrogen-containing
organic compounds decreased and the organic PM1 O:C ratio increased,
suggesting atmospheric bleaching of the BrC components. The organic PM1
was separated into six different classes by positive-matrix factorization
(PMF), and the mass absorption efficiency Eabs associated with each
factor was estimated through multivariate linear regression of
babs,BrC on the factor loadings. The largest Eabs values were
associated with urban (2.04±0.14 m2 g−1) and biomass-burning
(0.82±0.04 to 1.50±0.07 m2 g−1) sources. Together, these sources contributed at least 80 % of
babs,BrC while accounting for 30 % to 40 % of the organic PM1 mass
concentration. In addition, a comparison of organic PM1 composition
between wet and dry seasons revealed that only part of the 9-fold
increase in mass concentration between the seasons can be attributed to
biomass burning. Biomass-burning factor loadings increased by 30-fold,
elevating its relative contribution to organic PM1 from about 10 % in
the wet season to 30 % in the dry season. However, most of the PM1
mass (>60 %) in both seasons was accounted for by biogenic
secondary organic sources, which in turn showed an 8-fold seasonal
increase in factor loadings. A combination of decreased wet deposition and
increased emissions and oxidant concentrations, as well as a positive
feedback on larger mass concentrations are thought to play a role in the
observed increases. Furthermore, fuzzy c-means clustering identified three
clusters, namely “baseline”, “event”, and “urban” to represent
different pollution influences during the dry season. The baseline cluster,
representing the dry season background, was associated with a mean mass
concentration of 9±3 µg m−3. This concentration increased
on average by 3 µg m−3 for both the urban and the event clusters.
The event cluster, representing an increased influence of biomass burning
and long-range transport of African volcanic emissions, was characterized by
remarkably high sulfate concentrations. The urban cluster, representing the
influence of Manaus emissions on top of the baseline, was characterized by
an organic PM1 composition that differed from the other two clusters.
The differences discussed suggest a shift in oxidation pathways as well as
an accelerated oxidation cycle due to urban emissions, in agreement with
findings for the wet season.
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.
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