Research underconstruction
Contents
- 1 Sources of Chinese air pollutants
- 2 Volatile organic compounds (VOCs): global and regional emissions and impacts
- 3 Secondary organic aerosols (SOA)
- 4 Chemistry-Climate interactions and Chemistry-Climate Model (CCM) development
- 5 Measurements of Chinese PM2.5 composition
- 6 Air-sea exchange of organic materials
- 7 Long-range transport of pollutants
Sources of Chinese air pollutants
Team members: Nan LI, Yue JIAN, Heng TIAN, Hansen CAO, Tzung-May FU
We simulated elemental carbon (EC) and organic carbon (OC) aerosols in China and compared model results to surface measurements at Chinese rural and background sites, with the goal of deriving “top-down” emission estimates of EC and OC, as well as better quantifying the secondary sources of OC. We included in the model state-of-the-science Chinese “bottom-up” emission inventories for EC (1.92 TgC/yr) and OC (3.95 TgC/yr), as well as updated secondary OC formation pathways. The average simulated annual mean EC concentration at rural and background sites was 1.1 μgC/m3, 56% lower than the observed 2.5 μgC/m3. The average simulated annual mean OC concentration at rural and background sites was 3.4 μgC/m3, 76% lower than the observed 14 μgC/m3. Multiple regression to fit surface monthly mean EC observations at rural and background sites yielded the best estimate of Chinese EC source of 3.05±0.78 TgC/yr. Based on the topdown EC emission estimate and observed seasonal primary OC/EC ratios, we estimated Chinese OC emissions to be 6.67±1.30 6.67±1.30 TgC/yr. Using these top-down estimates, the simulated average annual mean EC concentration at rural and background sites was significantly improved to 1.9 μgC/m3. However, the model still significantly underestimated observed OC in all seasons (simulated average annual mean OC at rural and background sites was 5.4 μgC/m3), with little skill in capturing the spatiotemporal variability. Secondary formation accounts for 21% of Chinese annual mean surface OC in the model, with isoprene being the most important precursor. In summer, as high as 62% of the observed surface OC may be due to secondary formation in eastern China. Our analysis points to four shortcomings in the current bottom-up inventories of Chinese carbonaceous aerosols: (1) the anthropogenic source is underestimated on a national scale, particularly for OC; (2) the spatiotemporal distributions of emissions are misrepresented; (3) there is a missing source in western China, likely associated with the use of biofuels or other low-quality fuels for heating; and (4) sources in fall are not well represented, either because the seasonal shifting of. emissions and/or secondary formation are poorly captured or because specific fall emission events are missing. In addition, secondary production of OC in China is severely underestimated. More regional measurements with better spatiotemporal coverage are needed to resolve these shortcomings.
Publication: Fu et al. (2012)
Publication: Li et al., in preparation.
Publication: Jian et al., in preparation.
Volatile organic compounds (VOCs): global and regional emissions and impacts
Team members: Hansen CAO, Heng TIAN
Volatile organic compounds (VOC) impact the oxidizing power of the atmosphere and produce ozone and secondary organic aerosols. VOCs are emitted into the atmosphere from both natural and anthropogenic activities, and quantifying these many overlapping sources can be a challenge. We use remote sensing (satellite) and in situ observations to make 'top-down' estimates of VOC emissions from different sources. We use chemical transport models to evaluate the impact of VOCs on tropospheric chemistry.
We construct global budgets of atmospheric glyoxal and methylglyoxal with the goal of quantifying their potential for global secondary organic aerosol (SOA) formation via irreversible uptake by aqueous aerosols and clouds. We conduct a detailed simulation of glyoxal and methylglyoxal in the GEOS-Chem global 3-D chemical transport model including our best knowledge of source and sink processes. Our resulting best estimates of the global sources of glyoxal and methylglyoxal are 45 Tg/a and 140 Tg/a, respectively. Oxidation of biogenic isoprene contributes globally 47% of glyoxal and 79% of methylglyoxal. The second most important precursors are acetylene (mostly anthropogenic) for glyoxal and acetone (mostly biogenic) for methylglyoxal. Both acetylene and acetone have long lifetimes and provide a source of dicarbonyls in the free troposphere. Atmospheric lifetimes of glyoxal and methylglyoxal in the model are 2.9 h and 1.6 h, respectively, mostly determined by photolysis. Simulated dicarbonyl concentrations in continental surface air at northern midlatitudes are in the range 10–100 ppt, consistent with in situ measurements. On a global scale, the highest concentrations are over biomass burning regions, in agreement with glyoxal column observations from the SCIAMACHY satellite instrument. SCIAMACHY and a few ship cruises also suggest a large marine source of dicarbonyls missing from our model. The global source of SOA from the irreversible uptake of dicarbonyls in GEOS-Chem is 11 Tg C/a, including 2.6 Tg C/a from glyoxal and 8 Tg C/a from methylglyoxal; 90% of this source takes place in clouds. The magnitude of the global SOA source from dicarbonyls is comparable to that computed in GEOS-Chem from the standard mechanism involving reversible partitioning of semivolatile products from the oxidation of monoterpenes, sesquiterpenes, isoprene, and aromatics.
Publication: Fu et al. [2008]
Publication: Fu et al. [2007]
Publication: Millet et al. [2007], Palmer et al. [2006]
Secondary organic aerosols (SOA)
Team members: Nan LI, Li XING, Tzung-May FU
Secondary organic aerosols (SOA) are the organic mass transferred into the particulate phase in the atmosphere. Many recent observations have found SOA concentrations to be much higher than can be explained by current models in most parts of the atmosphere.
Using a global 3-D atmospheric chemistry model, we investigate the missing source of SOA. In particular, we find that the heteorogeneous uptake of dicarbonyls in aeorsols and clouds can help explained the observed SOA concentrations and variability.
We construct global budgets of atmospheric glyoxal and methylglyoxal with the goal of quantifying their potential for global secondary organic aerosol (SOA) formation via irreversible uptake by aqueous aerosols and clouds. We conduct a detailed simulation of glyoxal and methylglyoxal in the GEOS-Chem global 3-D chemical transport model including our best knowledge of source and sink processes. Our resulting best estimates of the global sources of glyoxal and methylglyoxal are 45 Tg/a and 140 Tg/a, respectively. Oxidation of biogenic isoprene contributes globally 47% of glyoxal and 79% of methylglyoxal. The second most important precursors are acetylene (mostly anthropogenic) for glyoxal and acetone (mostly biogenic) for methylglyoxal. Both acetylene and acetone have long lifetimes and provide a source of dicarbonyls in the free troposphere. Atmospheric lifetimes of glyoxal and methylglyoxal in the model are 2.9 h and 1.6 h, respectively, mostly determined by photolysis. Simulated dicarbonyl concentrations in continental surface air at northern midlatitudes are in the range 10–100 ppt, consistent with in situ measurements. On a global scale, the highest concentrations are over biomass burning regions, in agreement with glyoxal column observations from the SCIAMACHY satellite instrument. SCIAMACHY and a few ship cruises also suggest a large marine source of dicarbonyls missing from our model. The global source of SOA from the irreversible uptake of dicarbonyls in GEOS-Chem is 11 Tg C/a, including 2.6 Tg C/a from glyoxal and 8 Tg C/a from methylglyoxal; 90% of this source takes place in clouds. The magnitude of the global SOA source from dicarbonyls is comparable to that computed in GEOS-Chem from the standard mechanism involving reversible partitioning of semivolatile products from the oxidation of monoterpenes, sesquiterpenes, isoprene, and aromatics.
Publication: Fu et al. [2008]
We simulated elemental carbon (EC) and organic carbon (OC) aerosols in China and compared model results to surface measurements at Chinese rural and background sites, with the goal of deriving “top-down” emission estimates of EC and OC, as well as better quantifying the secondary sources of OC. We included in the model state-of-the-science Chinese “bottom-up” emission inventories for EC (1.92 TgC/yr) and OC (3.95 TgC/yr), as well as updated secondary OC formation pathways. The average simulated annual mean EC concentration at rural and background sites was 1.1 μgC/m3, 56% lower than the observed 2.5 μgC/m3. The average simulated annual mean OC concentration at rural and background sites was 3.4 μgC/m3, 76% lower than the observed 14 μgC/m3. Multiple regression to fit surface monthly mean EC observations at rural and background sites yielded the best estimate of Chinese EC source of 3.05±0.78 TgC/yr. Based on the topdown EC emission estimate and observed seasonal primary OC/EC ratios, we estimated Chinese OC emissions to be 6.67±1.30 6.67±1.30 TgC/yr. Using these top-down estimates, the simulated average annual mean EC concentration at rural and background sites was significantly improved to 1.9 μgC/m3. However, the model still significantly underestimated observed OC in all seasons (simulated average annual mean OC at rural and background sites was 5.4 μgC/m3), with little skill in capturing the spatiotemporal variability. Secondary formation accounts for 21% of Chinese annual mean surface OC in the model, with isoprene being the most important precursor. In summer, as high as 62% of the observed surface OC may be due to secondary formation in eastern China. Our analysis points to four shortcomings in the current bottom-up inventories of Chinese carbonaceous aerosols: (1) the anthropogenic source is underestimated on a national scale, particularly for OC; (2) the spatiotemporal distributions of emissions are misrepresented; (3) there is a missing source in western China, likely associated with the use of biofuels or other low-quality fuels for heating; and (4) sources in fall are not well represented, either because the seasonal shifting of. emissions and/or secondary formation are poorly captured or because specific fall emission events are missing. In addition, secondary production of OC in China is severely underestimated. More regional measurements with better spatiotemporal coverage are needed to resolve these shortcomings.
Publication: Fu et al. (2012)
Publication: Xing et al. (2013) aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
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Publication: Xing et al. (2013)
Chemistry-Climate interactions and Chemistry-Climate Model (CCM) development
Team members: Jinxuan CHEN, Yaping MA, Wanying KANG, Aoxing ZHANG, Ye QING
Publication:
Measurements of Chinese PM2.5 composition
Team members: Wei XU, Jinxuan CHEN, Heng TIAN, Aoxing ZHANG
Air-sea exchange of organic materials
Team members: Cenlin HE, Tzung-May FU
The ocean can act both as a source and a sink of atmospheric organic material. The air/sea exchange of organic materials is complexly regulated by both physical and biological conditions at the interface and poorly understood. We developed a new conceptual model to account for these physical and biological processes, including the presence of microfilms, production/consumption of organic matter by marine life, and other photochemical processes.
Publications: He and Fu (2013)
Long-range transport of pollutants
Team member: Yue JIAN
Publication: Jian and Fu (2014)
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