scholarly journals Modeling anthropogenically-controled secondary organic aerosols in a megacity: a simplified framework for global and climate models

2011 ◽  
Vol 4 (2) ◽  
pp. 869-905
Author(s):  
A. Hodzic ◽  
J. L. Jimenez
Keyword(s):  
Mexico City ◽  
Biomass Burning ◽  
Climate Models ◽  
Transport Model ◽  
Anthropogenic Pollution ◽  
Organic Aerosol ◽  
Temporal Variations ◽  
Anthropogenic Sources ◽  
Organic Vapors ◽  
Chemistry Transport Model

Abstract. A simplified parameterization for secondary organic aerosol (SOA) formation in polluted air and biomass burning smoke is tested and optimized in this work, towards the goal of a computationally inexpensive method to calculate pollution and biomass burning SOA in global and climate models. A regional chemistry-transport model is used as the testbed for the parameterization, which is compared against observations from the Mexico City metropolitan area during the MILAGRO 2006 field experiment. The empirical parameterization is based on the observed proportionality of SOA concentrations to excess CO and photochemical age of the airmass. The approach consists in emitting an organic gas as lumped SOA precursor surrogate proportional to anthropogenic or biomass burning CO emissions according to the observed ratio between SOA and CO in aged air, and reacting this surrogate with OH into a single non-volatile species that condenses to form SOA. An emission factor of 0.08 g of the lumped SOA precursor per g of CO and a rate constant with OH of 1.25 × 10−11 cm3 molecule−1 s−1 reproduce the observed average SOA mass within 30% in the urban area and downwind. When a 2.5 times slower rate is used (5 × 10−12 cm3 molecule−1 s−1) the predicted SOA amount and temporal evolution is nearly identical to the results obtained with SOA formation from semi-volatile and intermediate volatility primary organic vapors according to the Robinson et al. (2007) formulation. Our simplified method has the advantage of being much less computationally expensive than Robinson-type methods, and can be used in regions where the emissions of SOA precursors are not yet available. As the aged pollution SOA/ΔCO ratios are rather consistent globally, this parameterization could be reasonably tested in and applied to other regions. The potential enhancement of biogenic SOA by anthropogenic pollution, which has been suggested to play a major role in global SOA formation, is also tested using two simple parameterizations. Our results suggest that the pollution enhancement of biogenic SOA could provide several μg m−3 of additional SOA, but does not however explain the concentrations or especially the spatial and temporal variations of measured SOA mass in the vicinity of Mexico City, which appears to be controlled by anthropogenic sources. The contribution of the biomass burning to the predicted SOA is less than 10% during the study period.

scholarly journals Modeling anthropogenically controlled secondary organic aerosols in a megacity: a simplified framework for global and climate models

2011 ◽  
Vol 4 (4) ◽  
pp. 901-917 ◽  
Author(s):  
A. Hodzic ◽  
J. L. Jimenez
Keyword(s):  
Mexico City ◽  
Biomass Burning ◽  
Climate Models ◽  
Transport Model ◽  
Anthropogenic Pollution ◽  
Temporal Variations ◽  
Anthropogenic Sources ◽  
Organic Vapors ◽  
Chemistry Transport Model ◽  
Evolution Of Oxygen

Abstract. A simplified parameterization for secondary organic aerosol (SOA) formation in polluted air and biomass burning smoke is tested and optimized in this work, towards the goal of a computationally inexpensive method to calculate pollution and biomass burning SOA mass and hygroscopicity in global and climate models. A regional chemistry-transport model is used as the testbed for the parameterization, which is compared against observations from the Mexico City metropolitan area during the MILAGRO 2006 field experiment. The empirical parameterization is based on the observed proportionality of SOA concentrations to excess CO and photochemical age of the airmass. The approach consists in emitting an organic gas as lumped SOA precursor surrogate proportional to anthropogenic or biomass burning CO emissions according to the observed ratio between SOA and CO in aged air, and reacting this surrogate with OH into a single non-volatile species that condenses to form SOA. An emission factor of 0.08 g of the lumped SOA precursor per g of CO and a rate constant with OH of 1.25 × 10−11 cm3 molecule−1 s−1 reproduce the observed average SOA mass within 30 % in the urban area and downwind. When a 2.5 times slower rate is used (5 × 10−12 cm3 molecule−1 s−1) the predicted SOA amount and temporal evolution is nearly identical to the results obtained with SOA formation from semi-volatile and intermediate volatility primary organic vapors according to the Robinson et al. (2007) formulation. Our simplified method has the advantage of being much less computationally expensive than Robinson-type methods, and can be used in regions where the emissions of SOA precursors are not yet available. As the aged SOA/ΔCO ratios are rather consistent globally for anthropogenic pollution, this parameterization could be reasonably tested in and applied to other regions. The evolution of oxygen-to-carbon ratio was also empirically modeled and the predicted levels were found to be in reasonable agreement with observations. The potential enhancement of biogenic SOA by anthropogenic pollution, which has been suggested to play a major role in global SOA formation, is also tested using two simple parameterizations. Our results suggest that the pollution enhancement of biogenic SOA could provide additional SOA, but does not however explain the concentrations or the spatial and temporal variations of measured SOA mass in the vicinity of Mexico City, which appears to be controlled by anthropogenic sources. The contribution of the biomass burning to the predicted SOA is less than 10% during the studied period.

scholarly journals Volatility basis-set approach simulation of organic aerosol formation in East Asia: implications for anthropogenic-biogenic interaction and controllable amounts

2014 ◽  
Vol 14 (5) ◽  
pp. 6203-6260 ◽  
Author(s):  
H. Matsui ◽  
M. Koike ◽  
Y. Kondo ◽  
A. Takami ◽  
J. D. Fast ◽  
...  
Keyword(s):  
East Asia ◽  
Organic Aerosol ◽  
Temporal Variations ◽  
Basis Set ◽  
Anthropogenic Sources ◽  
Aerosol Formation ◽  
Organic Vapors ◽  
Mass Spectrometers ◽  
High Fraction ◽  
Outflow Region

Abstract. Organic aerosol (OA) simulations using the volatility basis-set approach were made for East Asia and its outflow region. Model simulations were evaluated through comparisons with OA measured by aerosol mass spectrometers in and around Tokyo (at Komaba and Kisai in summer 2003 and 2004) and over the outflow region in East Asia (at Fukue and Hedo in spring 2009). The simulations with aging processes of organic vapors reasonably well reproduced mass concentrations, temporal variations, and formation efficiency of observed OA at all sites. As OA mass was severely underestimated in the simulations without the aging processes, the oxidations of organic vapors are essential for reasonable OA simulations over East Asia. By considering the aging processes, simulated OA concentrations increased from 0.24 to 1.28 μg m−3 in the boundary layer over the whole of East Asia. OA formed from the interaction of anthropogenic and biogenic sources was also enhanced by the aging processes. The fraction of controllable OA was estimated to be 87% of total OA over the whole of East Asia, showing that most of the OA in our simulations formed anthropogenically (controllable). Even a large portion of biogenic secondary OA (78% of biogenic secondary OA) was formed through the influence of anthropogenic sources. The high fraction of controllable OA in our simulations is likely because anthropogenic emissions are dominant over East Asia and OA formation is enhanced by anthropogenic sources and their aging processes. Both the amounts (from 0.18 to 1.12 μg m−3) and the fraction (from 75% to 87%) of controllable OA were increased by aging processes of organic vapors over East Asia.

scholarly journals Sources and production of organic aerosol in Mexico City: insights from the combination of a chemical transport model (PMCAMx-2008) and measurements during MILAGRO

2011 ◽  
Vol 11 (11) ◽  
pp. 5153-5168 ◽  
Author(s):  
A. P. Tsimpidi ◽  
V. A. Karydis ◽  
M. Zavala ◽  
W. Lei ◽  
N. Bei ◽  
...  
Keyword(s):  
Mexico City ◽  
Biomass Burning ◽  
Urban Areas ◽  
Transport Model ◽  
Three Dimensional ◽  
Chemical Transport ◽  
Organic Aerosol ◽  
Basis Set ◽  
Chemical Transport Model ◽  
Aerosol Mass

Abstract. Urban areas are large sources of organic aerosols and their precursors. Nevertheless, the contributions of primary (POA) and secondary organic aerosol (SOA) to the observed particulate matter levels have been difficult to quantify. In this study the three-dimensional chemical transport model PMCAMx-2008 is used to investigate the temporal and geographic variability of organic aerosol in the Mexico City Metropolitan Area (MCMA) during the MILAGRO campaign that took place in the spring of 2006. The organic module of PMCAMx-2008 includes the recently developed volatility basis-set framework in which both primary and secondary organic components are assumed to be semi-volatile and photochemically reactive and are distributed in logarithmically spaced volatility bins. The MCMA emission inventory is modified and the POA emissions are distributed by volatility based on dilution experiments. The model predictions are compared with observations from four different types of sites, an urban (T0), a suburban (T1), a rural (T2), and an elevated site in Pico de Tres Padres (PTP). The performance of the model in reproducing organic mass concentrations in these sites is encouraging. The average predicted PM1 organic aerosol (OA) concentration in T0, T1, and T2 is 18 μg m−3, 11.7 μg m−3, and 10.5 μg m−3 respectively, while the corresponding measured values are 17.2 μg m−3, 11 μg m−3, and 9 μg m−3. The average predicted locally-emitted primary OA concentrations, 4.4 μg m−3 at T0, 1.2 μg m−3 at T1 and 1.7 μg m−3 at PTP, are in reasonably good agreement with the corresponding PMF analysis estimates based on the Aerosol Mass Spectrometer (AMS) observations of 4.5, 1.3, and 2.9 μg m−3 respectively. The model reproduces reasonably well the average oxygenated OA (OOA) levels in T0 (7.5 μg m−3 predicted versus 7.5 μg m−3 measured), in T1 (6.3 μg m−3 predicted versus 4.6 μg m−3 measured) and in PTP (6.6 μg m−3 predicted versus 5.9 μg m−3 measured). The rest of the OA mass (6.1 μg m−3 and 4.2 μg m−3 in T0 and T1 respectively) is assumed to originate from biomass burning activities and is introduced to the model as part of the boundary conditions. Inside Mexico City (at T0), the locally-produced OA is predicted to be on average 60 % locally-emitted primary (POA), 6 % semi-volatile (S-SOA) and intermediate volatile (I-SOA) organic aerosol, and 34 % traditional SOA from the oxidation of VOCs (V-SOA). The average contributions of the OA components to the locally-produced OA for the entire modelling domain are predicted to be 32 % POA, 10 % S-SOA and I-SOA, and 58 % V-SOA. The long range transport from biomass burning activities and other sources in Mexico is predicted to contribute on average almost as much as the local sources during the MILAGRO period.

scholarly journals Volatility basis-set approach simulation of organic aerosol formation in East Asia: implications for anthropogenic–biogenic interaction and controllable amounts

2014 ◽  
Vol 14 (18) ◽  
pp. 9513-9535 ◽  
Author(s):  
H. Matsui ◽  
M. Koike ◽  
Y. Kondo ◽  
A. Takami ◽  
J. D. Fast ◽  
...  
Keyword(s):  
East Asia ◽  
Organic Aerosol ◽  
Temporal Variations ◽  
Basis Set ◽  
Anthropogenic Sources ◽  
Aerosol Formation ◽  
Organic Vapors ◽  
Mass Spectrometers ◽  
Oxidation Rates ◽  
Outflow Region

Abstract. Organic aerosol (OA) simulations using the volatility basis-set approach were made for East Asia and its outflow region. Model simulations were evaluated through comparisons with OA measured by aerosol mass spectrometers in and around Tokyo (at Komaba and Kisai in summer 2003 and 2004) and over the outflow region in East Asia (at Fukue and Hedo in spring 2009). The simulations with aging processes of organic vapors reproduced the mass concentrations, temporal variations, and formation efficiencies of observed OA at all of the sites reasonably well. As OA mass was severely underestimated in the simulations without the aging processes, the oxidations of organic vapors are essential for reasonable OA simulations over East Asia. By considering the aging processes, simulated OA concentrations increased from 0.24 to 1.28 μg m−3 in the boundary layer over the whole of East Asia. OA formed from the interaction of anthropogenic and biogenic sources was also enhanced by the aging processes. The fraction of controllable OA was estimated to be 87% of total OA over the whole of East Asia, which indicated that most of the OA in our simulations were formed anthropogenically (from controllable combustion sources). A large portion of biogenic secondary OA (78% of biogenic secondary OA) was formed through the influence of anthropogenic sources. These fractions were higher than the fraction of anthropogenic emissions. An important reason for these higher controllable fractions was higher oxidant concentrations and the resulting faster oxidation rates of OA precursors by considering anthropogenic sources. Both the amounts (from 0.18 to 1.12 μg m−3) and the fraction (from 75 to 87%) of controllable OA were increased by aging processes of organic vapors over East Asia.

scholarly journals Aerosol mass spectrometer constraint on the global secondary organic aerosol budget

2011 ◽  
Vol 11 (2) ◽  
pp. 5699-5755 ◽  
Author(s):  
D. V. Spracklen ◽  
J. L. Jimenez ◽  
K. S. Carslaw ◽  
D. R. Worsnop ◽  
M. J. Evans ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Biomass Burning ◽  
Secondary Organic Aerosol ◽  
Transport Model ◽  
Anthropogenic Pollution ◽  
Organic Aerosol ◽  
Chemical Transport Model ◽  
Aerosol Mass Spectrometer ◽  
Aerosol Mass ◽  
Global Mean

Abstract. The budget of atmospheric secondary organic aerosol (SOA) is very uncertain, with recent estimates suggesting a global source of between 12 and 1820 Tg (SOA) a−1. We used a dataset of aerosol mass spectrometer (AMS) observations and a global chemical transport model including aerosol microphysics to produce top-down constraints on the SOA budget. We treated SOA formation from biogenic (monoterpenes and isoprene), lumped anthropogenic and lumped biomass burning volatile organic compounds (VOCs) and varied the SOA yield from each precursor source to produce the best overall match between model and observations. Organic aerosol observations from the IMPROVE network were used as an independent check of our optimised sources. The optimised model has a global SOA source of 140 ± 90 Tg (SOA) a−1 comprised of 13 ± 8 Tg (SOA) a−1 from biogenic, 100 ± 60 Tg (SOA) a−1 from anthropogenically controlled SOA, 23 ± 15 Tg (SOA) a−1 from conversion of primary organic aerosol (mostly from biomass burning) to SOA and an additional 3 ± 3 Tg (SOA) a−1 from biomass burning VOCs. Compared with previous estimates, our optimized model has a substantially larger SOA source in the Northern Hemisphere mid-latitudes. We used a dataset of 14C observations from rural locations to estimate that 10 Tg (SOA) a−1 (10%) of our anthropogenically controlled SOA is of urban/industrial origin, with 90 Tg (SOA) a−1 (90%) most likely due to an anthropogenic pollution enhancement of SOA from biogenic VOCs, almost an order-of-magnitude beyond what can be explained by current understanding. The urban/industrial SOA source is consistent with the 13 Tg a−1 estimated by de Gouw and Jimenez (2009), which was much larger than estimates from previous studies. The anthropogenically controlled SOA source results in a global mean aerosol direct effect of −0.26 ± 0.15 Wm−2 and global mean indirect (cloud albedo) effect of −0.6+0.24−0.14 Wm−2. The biogenic and biomass SOA sources are not well constrained due to the limited number of OA observations in regions and periods strongly impacted by these sources. To further improve the constraints by this method, additional observations are needed in the tropics and the Southern Hemisphere.

scholarly journals Can 3-D models explain the observed fractions of fossil and non-fossil carbon in and near Mexico City?

2010 ◽  
Vol 10 (22) ◽  
pp. 10997-11016 ◽  
Author(s):  
A. Hodzic ◽  
J. L. Jimenez ◽  
A. S. H. Prévôt ◽  
S. Szidat ◽  
J. D. Fast ◽  
...  
Keyword(s):  
Mexico City ◽  
Biomass Burning ◽  
Transport Model ◽  
Measurement Techniques ◽  
Independent Set ◽  
Temporal Variations ◽  
Total Carbon ◽  
High Time Resolution ◽  
Carbonaceous Aerosols ◽  
Fossil Carbon

Abstract. A 3-D chemistry-transport model has been applied to the Mexico City metropolitan area to investigate the origin of elevated levels of non-fossil (NF) carbonaceous aerosols observed in this highly urbanized region. High time resolution measurements of the fine aerosol concentration and composition, and 12 or 24 h integrated 14C measurements of aerosol modern carbon have been performed in and near Mexico City during the March 2006 MILAGRO field experiment. The non-fossil carbon fraction (fNF), which is lower than the measured modern fraction (fM) due to the elevated 14C in the atmosphere caused by nuclear bomb testing, is estimated from the measured fM and the source-dependent information on modern carbon enrichment. The fNF contained in PM1 total carbon analyzed by a US team (fNFTC) ranged from 0.37 to 0.67 at the downtown location, and from 0.50 to 0.86 at the suburban site. Substantially lower values (i.e. 0.24–0.49) were found for PM10 filters downtown by an independent set of measurements (Swiss team), which are inconsistent with the modeled and known differences between the size ranges, suggesting higher than expected uncertainties in the measurement techniques of 14C. An increase in the non-fossil organic carbon (OC) fraction (fNFOC) by 0.10–0.15 was observed for both sets of filters during periods with enhanced wildfire activity in comparison to periods when fires were suppressed by rain, which is consistent with the wildfire impacts estimated with other methods. Model results show that the relatively high fraction of non-fossil carbon found in Mexico City seems to arise from the combination in about equal proportions of regional biogenic SOA, biomass burning POA and SOA, as well as non-fossil urban POA and SOA. Predicted spatial and temporal variations for fNFOCare similar to those in the measurements between the urban vs. suburban sites, and high-fire vs. low-fire periods. The absolute modeled values of fNFOC are consistent with the Swiss dataset but lower than the US dataset. Resolving the 14C measurement discrepancies is necessary for further progress in model evaluation. The model simulations that included secondary organic aerosol (SOA) formation from semi-volatile and intermediate volatility (S/IVOC) vapors showed improved closure for the total OA mass compared to simulations which only included SOA from VOCs, providing a more realistic basis to evaluate the fNF predictions. fNFOC urban sources of modern carbon are important in reducing or removing the difference in fNF between model and measurements, even though they are often neglected on the interpretation of 14C datasets. An underprediction of biomass burning POA by the model during some mornings also explains a part of the model-measurement differences. The fNF of urban POA and SOA precursors is an important parameter that needs to be better constrained by measurements. Performing faster (≤3 h) 14C measurements in future campaigns is critical to further progress in this area. To our knowledge this is the first time that radiocarbon measurements are used together with aerosol mass spectrometer (AMS) organic components to assess the performance of a regional model for organic aerosols.

scholarly journals Modelling organic aerosol over Europe in summer conditions with the VBS-GECKO parameterization: sensitivity to secondary organic compound properties and IVOC emissions

2019 ◽  
Author(s):  
Victor Lannuque ◽  
Florian Couvidat ◽  
Marie Camredon ◽  
Bernard Aumont ◽  
Bertrand Bessagnet
Keyword(s):  
Urban Areas ◽  
Transport Model ◽  
Organic Aerosol ◽  
Anthropogenic Sources ◽  
Chemistry Transport Model ◽  
Continental Scale ◽  
Model Configuration ◽  
Vehicle Fleet ◽  
Light Gasoline ◽  
Terpene Oxidation

Abstract. The VBS-GECKO parameterization for secondary organic aerosol (SOA) formation was integrated in the chemistry-transport model CHIMERE. Concentrations of organic aerosol (OA) and SOA were simulated over Europe for the July–August 2013 period. Simulated concentrations with the VBS-GECKO were compared to results obtained with the former H2O parameterization implemented in CHIMERE and to observations from EMEP, ACTRIS and other observations available in the EBAS database. The model configuration using the VBS-GECKO parameterization slightly improves the performances compared to the model configuration using the former H2O parameterisation. The VBS-GECKO model configuration performs well for stations showing a large SOA concentration from biogenic sources, especially in northern Europe but underestimate OA concentrations over stations close to urban areas. Simulated OA was found to be mainly secondary (~ 85 %) and from terpene oxidation. Simulations show negligible contribution of the oxidation of mono-aromatic compounds to SOA production. Tests performed to examine the sensitivity of simulated OA concentrations to hydro-solubility, volatility, ageing rates and NOx regime have shown that the VBS-GECKO parameterization provides consistent results, with a weak sensitivity to changes in the parameters provided by the gas phase mechanism included in CHIMERE (e.g. HOx or NOx concentrations). Different emission scenarios (from heavy diesel to light gasoline fleet) were tested to examine the contribution of S/IVOC oxidation to SOA production. At the continental scale, these simulations show a weak sensitivity of OA concentrations to the vehicle fleet. At the local scale, accounting for IVOC emission was found to lead to a substantial increase of OA concentrations in the plume from urban areas, especially if diesel fleet case is assumed. This additional OA source remains too small to explain the gap between simulated and measured values at stations where anthropogenic sources are dominant.

scholarly journals Influences of hydroxyl radicals (OH) on top-down estimates of the global and regional methane budgets

2020 ◽  
Author(s):  
Yuanhong Zhao ◽  
Marielle Saunois ◽  
Philippe Bousquet ◽  
Xin Lin ◽  
Antoine Berchet ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Climate Models ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Temporal Variations ◽  
Oh Radicals ◽  
Chemical Transport Model ◽  
Top Down ◽  
Ch4 Emissions ◽  
The Impact

Abstract. The hydroxyl radical (OH), which is the dominant sink of methane (CH4), plays a key role to close the global methane budget. Previous research that assessed the impact of OH changes on the CH4 budget mostly relied on box modeling inversions with a very simplified atmospheric transport and no representation of the heterogeneous spatial distribution of OH radicals. Here using a variational Bayesian inversion framework and a 3D chemical transport model, LMDz, combined with 10 different OH fields derived from chemistry-climate models (CCMI experiment), we evaluate the influence of OH burden, spatial distribution, and temporal variations on the global CH4 budget. The global tropospheric mean CH4-reaction-weighted [OH] ([OH]GM-CH4) ranges 10.3–16.3 × 105 molec cm−3 across 10 OH fields during the early 2000s, resulting in inversion-based global CH4 emissions between 518 and 757 Tg yr−1. The uncertainties in CH4 inversions induced by the different OH fields are comparable to, or even larger than the uncertainty typically given by bottom-up and top-down estimates. Based on the LMDz inversions, we estimate that a 1 %-increase in OH burden leads to an increase of 4 Tg yr−1 in the estimate of global methane emissions, which is about 25 % smaller than what is estimated by box-models. The uncertainties in emissions induced by OH are largest over South America, corresponding to large inter-model differences of [OH] in this region. From the early to the late 2000s, the optimized CH4 emissions increased by 21.9 ± 5.7 Tg yr−1 (16.6–30.0 Tg yr−1), of which ~ 25 % (on average) is contributed by −0.5 to +1.8 % increase in OH burden. If the CCMI models represent the OH trend properly over the 2000s, our results show that a higher increasing trend of CH4 emissions is needed to match the CH4 observations compared to the CH4 emission trend derived using constant OH. This study strengthens the importance to reach a better representation of OH burden and of OH spatial and temporal distributions to reduce the uncertainties on the global CH4 budget.

scholarly journals Sources of Springtime Surface Black Carbon in the Arctic: An Adjoint Analysis

2017 ◽  
Author(s):  
Ling Qi ◽  
Qinbin Li ◽  
Daven K. Henze ◽  
Hsien-Liang Tseng ◽  
Cenlin He
Keyword(s):  
Natural Gas ◽  
Black Carbon ◽  
Biomass Burning ◽  
Transport Model ◽  
Lower Troposphere ◽  
Anthropogenic Sources ◽  
The Arctic ◽  
Anthropogenic Source ◽  
Gas Flaring ◽  
Arctic Front

Abstract. We quantify source contributions to springtime (April 2008) surface black carbon (BC) in the Arctic by interpreting surface observations of BC at five receptor sites (Denali, Barrow, Alert, Zeppelin, and Summit) using a global chemical transport model (GEOS-Chem) and its adjoint. Contributions to BC at Barrow, Alert, and Zeppelin are dominated by Asian anthropogenic sources (40–43 %) before April 18 and by Siberian open biomass burning emissions (29–41 %) afterward. In contrast, Summit, a mostly free tropospheric site, has predominantly an Asian anthropogenic source contribution (24–68 %, with an average of 45 %). We compute the adjoint sensitivity of BC concentrations at the five sites during a pollution episode (April 20–25) to global emissions from March 1 to April 25. The associated contributions are the combined results of these sensitivities and BC emissions. Local and regional anthropogenic sources in Alaska are the largest anthropogenic sources of BC at Denali (63 %), and natural gas flaring emissions in the Western Extreme North of Russia (WENR) are the largest anthropogenic sources of BC at Zeppelin (26 %) and Alert (13 %). We find that long-range transport of emissions from Beijing-Tianjin-Hebei (also known as Jing-Jin-Ji), the biggest urbanized region in Northern China, contribute significantly (~ 10 %) to surface BC across the Arctic. On average it takes ~ 12 days for Asian anthropogenic emissions and Siberian biomass burning emissions to reach Arctic lower troposphere, supporting earlier studies. Natural gas flaring emissions from the WENR reach Zeppelin in about a week. We find that episodic, direct transport events dominate BC at Denali (87 %), a site outside the Arctic front, a strong transport barrier. The relative contribution of direct transport to surface BC within the Arctic front is much smaller (~ 50 % at Barrow and Zeppelin and ~ 10 % at Alert). The large contributions from Asian anthropogenic sources are predominately in the form of ‘chronic’ pollution (~ 40 % at Barrow and 65 % at Alert and 57 % at Zeppelin) on 1–2 month timescales. As such, it is likely that previous studies using 5- or 10-day trajectory analyses strongly underestimated the contribution from Asia to surface BC in the Arctic. Both finer temporal resolution of biomass burning emissions and accounting for the Wegener-Bergeron-Findeisen (WBF) process in wet scavenging improve the source attribution estimates.

scholarly journals The influence of biogenic emissions on upper-tropospheric methanol as revealed from space

2007 ◽  
Vol 7 (24) ◽  
pp. 6119-6129 ◽  
Author(s):  
G. Dufour ◽  
S. Szopa ◽  
D. A. Hauglustaine ◽  
C. D. Boone ◽  
C. P. Rinsland ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Biomass Burning ◽  
Transport Model ◽  
Tropospheric Chemistry ◽  
Biogenic Emissions ◽  
Chemistry Transport Model ◽  
Mixing Ratios ◽  
Oxygenated Compounds ◽  
Global Space ◽  
The Impact

Abstract. The distribution and budget of oxygenated organic compounds in the atmosphere and their impact on tropospheric chemistry are still poorly constrained. Near-global space-borne measurements of seasonally resolved upper tropospheric profiles of methanol (CH3OH) by the ACE Fourier transform spectrometer provide a unique opportunity to evaluate our understanding of this important oxygenated organic species. ACE-FTS observations from March 2004 to August 2005 period are presented. These observations reveal the pervasive imprint of surface sources on upper tropospheric methanol: mixing ratios observed in the mid and high latitudes of the Northern Hemisphere reflect the seasonal cycle of the biogenic emissions whereas the methanol cycle observed in the southern tropics is highly influenced by biomass burning emissions. The comparison with distributions simulated by the state-of-the-art global chemistry transport model, LMDz-INCA, suggests that: (i) the background methanol (high southern latitudes) is correctly represented by the model considering the measurement uncertainties; (ii) the current emissions from the continental biosphere are underestimated during spring and summer in the Northern Hemisphere leading to an underestimation of modelled upper tropospheric methanol; (iii) the seasonal variation of upper tropospheric methanol is shifted to the fall in the model suggesting either an insufficient destruction of CH3OH (due to too weak chemistry and/or deposition) in fall and winter months or an unfaithful representation of transport; (iv) the impact of tropical biomass burning emissions on upper tropospheric methanol is rather well reproduced by the model. This study illustrates the potential of these first global profile observations of oxygenated compounds in the upper troposphere to improve our understanding of their global distribution, fate and budget.

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