Importance of transboundary transport of biomass burning emissions to regional air quality in Southeast Asia during a high fire event

10.5194/acp-15-363-2015Atmospheric Chemistry and Physics151363-37

Continental-Scale Partitioning of Fire Emissions During the 1997 to 2001 El Niño/La Niña Period

During the 1997 to 1998 El Niño, drought conditions triggered widespread increases in fire activity, releasing CH_4 and CO_2 to the atmosphere. We evaluated the contribution of fires from different continents to variability in these greenhouse gases from 1997 to 2001, using satellite-based estimates of fire activity, biogeochemical modeling, and an inverse analysis of atmospheric CO anomalies. During the 1997 to 1998 El Niño, the fire emissions anomaly was 2.1 ± 0.8 petagrams of carbon, or 66 ± 24% of the CO_2 growth rate anomaly. The main contributors were Southeast Asia (60%), Central and South America (30%), and boreal regions of Eurasia and North America (10%)

New land-use-change emissions indicate a declining CO₂ airborne fraction

About half of the anthropogenic CO2 emissions remain in the atmosphere and half are taken up by the land and ocean1. If the carbon uptake by land and ocean sinks becomes less efficient, for example, owing to warming oceans2 or thawing permafrost3, a larger fraction of anthropogenic emissions will remain in the atmosphere, accelerating climate change. Changes in the efficiency of the carbon sinks can be estimated indirectly by analysing trends in the airborne fraction, that is, the ratio between the atmospheric growth rate and anthropogenic emissions of CO2 (refs. 4–10). However, current studies yield conflicting results about trends in the airborne fraction, with emissions related to land use and land cover change (LULCC) contributing the largest source of uncertainty7,11,12. Here we construct a LULCC emissions dataset using visibility data in key deforestation zones. These visibility observations are a proxy for fire emissions13,14, which are — in turn — related to LULCC15,16. Although indirect, this provides a long-term consistent dataset of LULCC emissions, showing that tropical deforestation emissions increased substantially (0.16 Pg C decade−1) since the start of CO2 concentration measurements in 1958. So far, these emissions were thought to be relatively stable, leading to an increasing airborne fraction4,5. Our results, however, indicate that the CO2 airborne fraction has decreased by 0.014 ± 0.010 decade−1 since 1959. This suggests that the combined land–ocean sink has been able to grow at least as fast as anthropogenic emissions

Top-down estimates of global CO sources using MOPITT measurements

We present a synthesis inversion of CO emissions from various geographical regions and for various source categories for the year 2000 using CO retrievals from the MOPITT (Measurements of Pollution in the Troposphere) instrument. We find a large discrepancy between our top‐down estimates and recent bottom‐up estimates of CO emissions from fossil fuel/biofuel (FFBF) use in Asia. A key conclusion of this study is that CO emissions in East Asia (EAS) are about a factor of 1.8–2 higher than recent bottom‐up estimates

Modeling vegetation fires and fire emissions

Fire is the most important ecological and forest disturbance agent worldwide, is a major way by which carbon is transferred from the land to the atmosphere, and is globally a significant source of greenhouse gases and aerosols. Wildfires across all major biome types globally consume about 5% of net annual terrestrial primary production per annum, and release about 2-4 Pg C per annum, of which approximately 0.6 Pg C comes from tropical deforestation and below-ground peat fires. The global figure is equivalent to about 20-30% of global emissions from fossil fuels. Tropical savannas comprise the largest areas burned and greatest emissions sources from vegetation wildfires. Fires in Mediterranean forests and shrublands, tropical forests and boreal forests are also significant sources of emissions because they are generally characterised by much higher fuel loads per unit area compared with grasslands. Improved satellite data and sophisticated biogeochemical modeling enables emis-sions assessments on a global scale with fine spatial and temporal resolution. Emissions estimates are still comparable to those based on older inventory-based techniques, but uncertainties remain large. Fires increase during El Niño periods because parts of the tropics where humans use fire as a tool for deforestation experience drought conditions. These spikes contribute to the inter-annual variability of CO2 and CH4 observed in the atmosphere. Recently developed dynamic fire-vegetation models are capable of simulating the extent of wildfires as well as their emissions of CO2 and other greenhouse gases for ambient as well as for projected climatic conditions. The performance of fire-vegetation models however needs to be strongly improved and validated

African burned area and fire carbon emissions are strongly impacted by small fires undetected by coarse resolution satellite data

Fires are a major contributor to atmospheric budgets of greenhouse gases and aerosols, affect soils and vegetation properties, and are a key driver of land use change. Since the 1990s, global burned area (BA) estimates based on satellite observations have provided critical insights into patterns and trends of fire occurrence. However, these global BA products are based on coarse spatial-resolution sensors, which are unsuitable for detecting small fires that burn only a fraction of a satellite pixel. We estimated the relevance of those small fires by comparing a BA product generated from Sentinel-2 MSI (Multispectral Instrument) images (20-m spatial resolution) with a widely used global BA product based on Moderate Resolution Imaging Spectroradiometer (MODIS) images (500 m) focusing on sub-Saharan Africa. For the year 2016, we detected 80% more BA with Sentinel-2 images than with the MODIS product. This difference was predominately related to small fires: we observed that 2.02 Mkm2 (out of a total of 4.89 Mkm2) was burned by fires smaller than 100 ha, whereas the MODIS product only detected 0.13 million km2 BA in that fire-size class. This increase in BA subsequently resulted in increased estimates of fire emissions; we computed 31 to 101% more fire carbon emissions than current estimates based on MODIS products. We conclude that small fires are a critical driver of BA in sub-Saharan Africa and that including those small fires in emission estimates raises the contribution of biomass burning to global burdens of (greenhouse) gases and aerosols

Adsorption of high density lipoproteins (HDL) on solid surfaces

The adsorption of high density lipoproteins (HDL) on polyethylene (PE), poly(2-hydroxyethyl methacrylate) (poly(HEMA)), polyesterurethane (PU), Biomer, and mica surfaces was studied. The adsorption of HDL from a single protein solution and a plasma solution on the surfaces showed that the amount of adsorbed HDL was not related to the hydrophobicity (or hydrophilicity) of the surfaces. It was observed that the amount of HDL adsorbed on PE increased with increasing HDL concentration of a single protein solution until 5 ¿g/ml, and increasing plasma concentration resulted in an increase of HDL adsorption. In addition, HDL adsorption from an HDL solution of 500 ¿g/ml on PE reached a maximum within a few minutes at 25°C. Only a proportion of adsorbed HDL could be desorbed when the adsorbed layers were incubated with Tween 20 or sodium dodecyl sulfate (SDS), while the desorption was dependent on the nature of the surfaces. It was more difficult to desorb HDL adsorbed from plasma to PE than to desorb HDL adsorbed from a single protein solution to PE. It was found that the desorption of adsorbed HDL from PE by the detergents was decreased if the protein layer had been stored in buffer (pH 7.4) for 24 h before desorption, while a higher storing temperature had a negative effect on the desorption of the lipoprotein from the surface. Adsorbed HDL on mica in a physiological buffer was imaged by a tapping mode atomic force microscope (AFM). The surface appeared to be covered by single HDL proteins as well as clusters of two or three HDL proteins with an average height of 5 to 6 nm. Furthermore, the partial desorption of adsorbed HDL from mica was confirmed by AFM measurements

Evaluation of cropland maximum light use efficiency using eddy flux measurements in North America and Europe

Croplands cover 12% of the ice-free land surface and play an important role in the global carbon cycle. Light use efficiency (LUE) models have often been employed to estimate the exchange of CO2 between croplands and the atmosphere. A key parameter in these models is the maximum light use efficiency (ε*), but estimates of ε* vary by at least a factor 2. Here we used 12 agricultural eddy-flux measurement sites in North America and Europe to constrain LUE models in general and ε* in particular. We found that LUE models could explain on average about 70% of the variability in net ecosystem exchange (NEE) when we increased the ε* from 0.5 to 0.65-2.0g C per MJ Photosynthetic Active Radiation (PAR). Our results imply that croplands are more important in the global carbon budget than often thought. In addition, inverse modeling approaches that utilize LUE model outputs as a-priori input may have to be revisited in areas where croplands are an important contributor to regional carbon fluxes. Copyright 2011 by the American Geophysical Union

Stable carbon isotopic composition of biomass burning emissions - implications for estimating the contribution of C-3 and C-4 plants

Landscape fires are a significant contributor to atmospheric burdens of greenhouse gases and aerosols. Although many studies have looked at biomass burning products and their fate in the atmosphere, estimating and tracing atmospheric pollution from landscape fires based on atmospheric measurements are challenging due to the large variability in fuel composition and burning conditions. Stable carbon isotopes in biomass burning (BB) emissions can be used to trace the contribution of C-3 plants (e.g. trees or shrubs) and C-4 plants (e.g. savanna grasses) to various combustion products. However, there are still many uncertainties regarding changes in isotopic composition (also known as fractionation) of the emitted carbon compared to the burnt fuel during the pyrolysis and combustion processes. To study BB isotope fractionation, we performed a series of laboratory fire experiments in which we burned pure C-3 and C-4 plants as well as mixtures of the two. Using isotope ratio mass spectrometry (IRMS), we measured stable carbon isotope signatures in the pre-fire fuels and post-fire residual char, as well as in the CO2, CO, CH4, organic carbon (OC), and elemental carbon (EC) emissions, which together constitute over 98 % of the post-fire carbon. Our laboratory tests indicated substantial isotopic fractionation in combustion products compared to the fuel, which varied between the measured fire products. CO2, EC, and residual char were the most reliable tracers of the fuel C-13 signature. CO in particular showed a distinct dependence on burning conditions; flaming emissions were enriched in C-13 compared to smouldering combustion emissions. For CH4 and( )OC, the fractionation was the other way round for C3 emissions (C-13-enriched) and C-4 emissions (C-13-depleted). This indicates that while it is possible to distinguish between fires that were dominated by either C-3 or C-4 fuels using these tracers, it is more complicated to quantify their relative contribution to a mixed-fuel fire based on the delta C-13 signature of emissions. Besides laboratory experiments, we sampled gases and carbonaceous aerosols from prescribed fires in the Niassa Special Reserve (NSR) in Mozambique, using an unmanned aerial system (UAS)-mounted sampling set-up. We also provided a range of C-3:C-4 contributions to the fuel and measured the fuel isotopic signatures. While both OC and EC were useful tracers of the C-3-to-C-4 fuel ratio in mixed fires in the lab, we found particularly OC to be depleted compared to the calculated fuel signal in the field experiments. This suggests that either our fuel measurements were incomprehensive and underestimated the C-3:C-4 ratio in the field or other processes caused this depletion. Although additional field measurements are needed, our results indicate that C-3-vs.-C-4 source ratio estimation is possible with most BB products, albeit with varying uncertainty ranges

Climate controls on the variability of fires in the tropics and subtropics

In the tropics and subtropics, most fires are set by humans for a wide range of purposes. The total amount of burned area and fire emissions reflects a complex interaction between climate, human activities, and ecosystem processes. Here we used satellite-derived data sets of active fire detections, burned area, precipitation, and the fraction of absorbed photosynthetically active radiation (fAPAR) during 1998-2006 to investigate this interaction. The total number of active fire detections and burned area was highest in areas that had intermediate levels of both net primary production (NPP; 500-1000 g C