Satellite observations indicate substantial spatiotemporal variability in biomass burning NOx emission factors for South America
Castellanos, P. ; Boersma, K.F. ; Werf, G.R. van de - \ 2014
Atmospheric Chemistry and Physics 14 (2014). - ISSN 1680-7316 - p. 3929 - 3943.
ozone monitoring instrument - fire emissions - trace gases - tropospheric chemistry - chemical-composition - nitrogen-dioxide - tropical forest - b experiment - model tm5 - brazil
Biomass burning is an important contributor to global total emissions of NOx (NO+NO2). Generally bottom-up fire emissions models calculate NOx emissions by multiplying fuel consumption estimates with static biome-specific emission factors, defined in units of grams of NO per kilogram of dry matter consumed. Emission factors are a significant source of uncertainty in bottom-up fire emissions modeling because relatively few observations are available to characterize the large spatial and temporal variability of burning conditions. In this paper we use NO2 tropospheric column observations from the Ozone Monitoring Instrument (OMI) from the year 2005 over South America to calculate monthly NOx emission factors for four fire types: deforestation, savanna/grassland, woodland, and agricultural waste burning. In general, the spatial patterns in NOx emission factors calculated in this work are consistent with emission factors derived from in situ measurements from the region but are more variable than published biome-specific global average emission factors widely used in bottom-up fire emissions inventories such as the Global Fire Emissions Database (GFED). Satellite-based NOx emission factors also indicate substantial temporal variability in burning conditions. Overall, we found that deforestation fires have the lowest NOx emission factors, on average 30% lower than the emission factors used in GFED v3. Agricultural fire NOx emission factors were the highest, on average a factor of 1.8 higher than GFED v3 values. For savanna, woodland, and deforestation fires, early dry season NOx emission factors were a factor of ~1.5–2 higher than late dry season emission factors. A minimum in the NOx emission factor seasonal cycle for deforestation fires occurred in August, the time period of severe drought in South America in 2005, supporting the hypothesis that prolonged dry spells may lead to an increase in the contribution of smoldering combustion from large-diameter fuels, offsetting the higher combustion efficiency of dryer fine fuels. We evaluated the OMI-derived NOx emission factors with SCIAMACHY NO2 tropospheric column observations and found improved model performance in regions dominated by fire emissions.
Emission ratio and isotopic signatures of molecular hydrogen emissions from tropical biomass burning
Haumann, F.A. ; Batenburg, A.M. ; Pieterse, G. ; Gerbig, C. ; Krol, M.C. ; Rockmann, T. - \ 2013
Atmospheric Chemistry and Physics 13 (2013)18. - ISSN 1680-7316 - p. 9401 - 9413.
atmospheric hydrogen - assimilation system - land-surface - amazon basin - trace gases - tall tower - model tm5 - h-2 - chemistry - plants
In this study, we identify a biomass-burning signal in molecular hydrogen (H-2) over the Amazonian tropical rainforest. To quantify this signal, we measure the mixing ratios of H-2 and several other species as well as the H-2 isotopic composition in air samples that were collected in the BARCA (Balanco Atmosferico Regional de Carbono na Amazonia) aircraft campaign during the dry season. We derive a relative H-2 emission ratio with respect to carbon monoxide (CO) of 0.31 +/- 0.04 ppb ppb(-1) and an isotopic source signature of -280 +/- 41 parts per thousand in the air masses influenced by tropical biomass burning. In order to retrieve a clear source signal that is not influenced by the soil uptake of H-2, we exclude samples from the atmospheric boundary layer. This procedure is supported by data from a global chemistry transport model. The Delta H-2/Delta CO emission ratio is significantly lower than some earlier estimates for the tropical rainforest. In addition, our results confirm the lower values of the previously conflicting estimates of the H-2 isotopic source signature from biomass burning. These values for the emission ratio and isotopic source signatures of H-2 from tropical biomass burning can be used in future bottom-up and top-down approaches aiming to constrain the strength of the biomass-burning source for H-2. Hitherto, these two quantities relied only on combustion experiments or on statistical relations, since no direct signal had been obtained from in-situ observations.
What could have caused pre-industrial biomass burning emissions to exceed current rates?
Werf, G.R. van der; Peters, W. ; Leeuwen, T.T. van; Giglio, L. - \ 2013
Climate of the Past 9 (2013)1. - ISSN 1814-9324 - p. 289 - 306.
rain-forest fires - past 2 millennia - amazonian forests - southern africa - trace gases - model tm5 - land-use - carbon - 20th-century - climate
Recent studies based on trace gas mixing ratios in ice cores and charcoal data indicate that biomass burning emissions over the past millennium exceeded contemporary emissions by up to a factor of 4 for certain time periods. This is surprising because various sources of biomass burning are linked with population density, which has increased over the past centuries. We have analysed how emissions from several landscape biomass burning sources could have fluctuated to yield emissions that are in correspondence with recent results based on ice core mixing ratios of carbon monoxide (CO) and its isotopic signature measured at South Pole station (SPO). Based on estimates of contemporary landscape fire emissions and the TM5 chemical transport model driven by present-day atmospheric transport and OH concentrations, we found that CO mixing ratios at SPO are more sensitive to emissions from South America and Australia than from Africa, and are relatively insensitive to emissions from the Northern Hemisphere. We then explored how various landscape biomass burning sources may have varied over the past centuries and what the resulting emissions and corresponding CO mixing ratio at SPO would be, using population density variations to reconstruct sources driven by humans (e.g., fuelwood burning) and a new model to relate savanna emissions to changes in fire return times. We found that to match the observed ice core CO data, all savannas in the Southern Hemisphere had to burn annually, or bi-annually in combination with deforestation and slash and burn agriculture exceeding current levels, despite much lower population densities and lack of machinery to aid the deforestation process. While possible, these scenarios are unlikely and in conflict with current literature. However, we do show the large potential for increased emissions from savannas in a pre-industrial world. This is mainly because in the past, fuel beds were probably less fragmented compared to the current situation; satellite data indicates that the majority of savannas have not burned in the past 10 yr, even in Africa, which is considered "the burning continent". Although we have not considered increased charcoal burning or changes in OH concentrations as potential causes for the elevated CO concentrations found at SPO, it is unlikely they can explain the large increase found in the CO concentrations in ice core data. Confirmation of the CO ice core data would therefore call for radical new thinking about causes of variable global fire rates over recent centuries
Interannual variability of carbon monoxide emission estimates over South America from 2006 to 2010
Hooghiemstra, P.B. ; Krol, M.C. ; Leeuwen, T.T. van; Werf, G.R. van der; Novelli, P.C. ; Deeter, M.N. ; Aben, I. ; Rockmann, T. - \ 2012
Journal of Geophysical Research: Atmospheres 117 (2012). - ISSN 2169-897X
variational data assimilation - land-use change - climate-change - co emissions - amazon deforestation - brazilian amazon - fire emissions - model tm5 - mopitt - inversion
We present the first inverse modeling study to estimate CO emissions constrained by both surface and satellite observations. Our 4D-Var system assimilates National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) surface and Measurements Of Pollution In The Troposphere (MOPITT) satellite observations jointly by fitting a bias correction scheme. This approach leads to the identification of a positive bias of maximum 5 ppb in MOPITT column-averaged CO mixing ratios in the remote Southern Hemisphere (SH). The 4D-Var system is used to estimate CO emissions over South America in the period 2006-2010 and to analyze the interannual variability (IAV) of these emissions. We infer robust, high spatial resolution CO emission estimates that show slightly smaller IAV due to fires compared to the Global Fire Emissions Database (GFED3) prior emissions. South American dry season (August and September) biomass burning emission estimates amount to 60, 92, 42, 16 and 93 Tg CO/yr for 2006 to 2010, respectively. Moreover, CO emissions probably associated with pre-harvest burning of sugar cane plantations in Sao Paulo state are underestimated in current inventories by 50-100%. We conclude that climatic conditions (such as the widespread drought in 2010) seem the most likely cause for the IAV in biomass burning CO emissions. However, socio-economic factors (such as the growing global demand for soy, beef and sugar cane ethanol) and associated deforestation fires, are also likely as drivers for the IAV of CO emissions, but are difficult to link directly to CO emissions.
Optimizing global CO emission estimates using a four-dimensional variational data assimilation system and surface network observations
Hooghiemstra, P.B. ; Krol, M.C. ; Meirink, J.F. ; Bergamaschi, P. ; Werf, G.R. van der; Novelli, P.C. ; Aben, I. ; Röckmann, T. - \ 2011
Atmospheric Chemistry and Physics 11 (2011)10. - ISSN 1680-7316 - p. 4705 - 4723.
carbon-monoxide - tropospheric chemistry - fire emissions - model tm5 - inversion - mopitt - adjoint - forest - asia - algorithm
We apply a four-dimensional variational (4D-VAR) data assimilation system to optimize carbon monoxide (CO) emissions for 2003 and 2004 and to reduce the uncertainty of emission estimates from individual sources using the chemistry transport model TM5. The system is designed to assimilate large (satellite) datasets, but in the current study only a limited amount of surface network observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) is used to test the 4D-VAR system. By design, the system is capable to adjust the emissions in such a way that the posterior simulation reproduces background CO mixing ratios and large-scale pollution events at background stations. Uncertainty reduction up to 60 % in yearly emissions is observed over well-constrained regions and the inferred emissions compare well with recent studies for 2004. However, with the limited amount of data from the surface network, the system becomes data sparse resulting in a large solution space. Sensitivity studies have shown that model uncertainties (e.g., vertical distribution of biomass burning emissions and the OH field) and the prior inventories used, influence the inferred emission estimates. Also, since the observations only constrain total CO emissions, the 4D-VAR system has difficulties in separating anthropogenic and biogenic sources in particular. The inferred emissions are validated with NOAA aircraft data over North America and the agreement is significantly improved from the prior to posterior simulation. Validation with the Measurements Of Pollution In The Troposphere (MOPITT) instrument version 4 (V4) shows a slight improved agreement over the well-constrained Northern Hemisphere and in the tropics (except for the African continent). However, the model simulation with posterior emissions underestimates MOPITT CO total columns on the remote Southern Hemisphere (SH) by about 10 %. This is caused by a reduction in SH CO sources mainly due to surface stations on the high southern latitudes.
Impact of CO2 measurement bias on CarbonTracker surface flux estimates
Masarie, K.A. ; Petron, G. ; Andrews, A. ; Bruhwiler, L. ; Conway, T.J. ; Jacobson, A.R. ; Miller, J.B. ; Tans, P.P. ; Worthy, D.E. ; Peters, W. - \ 2011
Journal of Geophysical Research: Atmospheres (2011). - ISSN 2169-897X - 13 p.
carbon-dioxide exchange - tall tower - model tm5 - atmospheric co2 - inversions - scale - air
For over 20 years, atmospheric measurements of CO2 dry air mole fractions have been used to derive estimates of CO2 surface fluxes. Historically, only a few research laboratories made these measurements. Today, many laboratories are making CO2 observations using a variety of analysis techniques and, in some instances, using different calibration scales. As a result, the risk of biases in individual CO2 mole fraction records, or even in complete monitoring networks, has increased over the last decades. Ongoing experiments comparing independent, well-calibrated measurements of atmospheric CO2 show that biases can and do exist between measurement records. Biases in measurements create artificial spatial and temporal CO2 gradients, which are then interpreted by an inversion system, leading to erroneous flux estimates. Here we evaluate the impact of a constant bias introduced into the National Oceanic and Atmospheric Administration (NOAA) quasi-continuous measurement record at the Park Falls, Wisconsin (LEF), tall tower site on CarbonTracker flux estimates. We derive a linear relationship between the magnitude of the introduced bias at LEF and the CarbonTracker surface flux responses. Temperate North American net flux estimates are most sensitive to a bias at LEF in our CarbonTracker inversion, and its linear response rate is 68 Tg C yr-1 (~10% of the estimated North American annual terrestrial uptake) for every 1 ppm of bias in the LEF record. This sensitivity increases when (1) measurement biases approached assumed model errors and (2) fewer other measurement records are available to anchor the flux estimates despite the presence of bias in one record. Flux estimate errors are also calculated beyond North America. For example, biospheric uptake in Europe and boreal Eurasia combined increases by 25 Tg C yr-1 per ppm CO2 to partially compensate for changes in the North American flux totals. These results illustrate the importance of well-calibrated, high-precision CO2 dry air mole fraction measurements, as well as the value of an effective strategy for detecting bias in measurements. This study stresses the need for a monitoring network with the necessary density to anchor regional, continental, and hemispheric fluxes more tightly and to lessen the impact of potentially undetected biases in observational networks operated by different national and international research programs.
Spatial distribution of Delta(CO2)-C-14 across Eurasia: measurements from the TROICA-8 expedition
Turnbull, J.C. ; Miller, J.B. ; Lehman, S.J. ; Hurst, D. ; Peters, W. - \ 2009
Atmospheric Chemistry and Physics 9 (2009)1. - ISSN 1680-7316 - p. 175 - 187.
fossil-fuel co2 - trans-siberian railroad - nuclear-power-plants - carbon-dioxide - (co2)-c-14 observations - atmospheric co2 - united-states - trace gases - model tm5 - c-14
Because fossil fuel derived CO2 is the only source of atmospheric CO2 that is devoid of 14C, atmospheric measurements of delta14CO2 can be used to constrain fossil fuel emission estimates at local and regional scales. However, at the continental scale, uncertainties in atmospheric transport and other sources of variability in delta14CO2 may influence the fossil fuel detection capability. We present a set of delta14CO2 observations from the train-based TROICA-8 expedition across Eurasia in March-April 2004. Local perturbations in delta14CO2 are caused by easily identifiable sources from nuclear reactors and localized pollution events. The remaining data show an increase in delta14CO2 from Western Russia (40° E) to Eastern Siberia (120° E), consistent with depletion in 14CO2 caused by fossil fuel CO2 emissions in heavily populated Europe, and gradual dispersion of the fossil fuel plume across Northern Asia. Other trace gas species which may be correlated with fossil fuel CO2 emissions, including carbon monoxide, sulphur hexafluoride, and perchloroethylene, were also measured and the results compared with the delta14CO2 measurements. The sulphur hexafluoride longitudinal gradient is not significant relative to the measurement uncertainty. Carbon monoxide and perchloroethylene show large-scale trends of enriched values in Western Russia and decreasing values in Eastern Siberia, consistent with fossil fuel emissions, but exhibit significant spatial variability, especially near their primary sources in Western Russia. The clean air delta14CO2 observations are compared with simulated spatial gradients from the TM5 atmospheric transport model. We show that the change in delta14CO2 across the TROICA transect is due almost entirely to emissions of fossil fuel CO2, but that the magnitude of this delta14CO2 gradient is relatively insensitive to modest uncertainties in the fossil fuel flux. In contrast, the delta14CO2 gradient is more sensitive to the modeled representation of vertical mixing, suggesting that delta14CO2 may be a useful tracer for training mixing in atmospheric transport models.