Considerations related to the Question: Do aerosols from biomass combustion contribute to global warming or global cooling?

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1 TITEL-FOLIE Expert Group on Techno-Economic Issues, EGTEI, Meeting Rome, Black carbon and brown carbon: Partitioning in biomass combustion and relevance for climate change Considerations related to the Question: Do aerosols from biomass combustion contribute to global warming or global cooling? Thomas Nussbaumer, Zurich Lucerne University of Applied Sciences SWITZERLAND

2 EC (BC), COC CO, VOC Primary org. Aerosols POA Secondary org. Aerosols SOA hν CC (salt) NO x PIA SIA PM 10 CO 2 C fix C Ca, K, Cl, N Ash CaO, KCl

3 Solid Particles & Condens. Gas phase emissions Salts Soot COC VOC CO CO 2 H 2 O Particle Sources [Schmid]

4 Particle Types Soot Salt COC ('Tar') C A B Excess Air Ratio λ [Nussbaumer, Energy & Fuels 2003, 17]

5 Particle Types Soot Salt COC ('Tar')

6 Effect of aerosols on climate change [IPCC 2007]

7 Effect of aerosols on climate change [IPCC 2007]

8 Effect of aerosols on climate change 1. Black Carbon strongly absorbs sunlight and has a strong warming effect. BC on ice and snow enhances the melting and changes the albedo. [IPCC 2007]: GWP = 460 x CO 2 for 100 years or 1006 x 20 years. [Bond 2007]: GWP 500 to 700 / 2000 times plus indirect effects. 2. Sulfates change albedo by reflecting sunlight and cool the earth surface. Salts from biomass may act similar if uncoated? 3. Organic carbon: [IPCC 2007]: Cooling which is app. 50% of the net warming effect of BC. [Bond 2007]: warming or slight cooling effect, > Net effect uncertain. Effect of coating is unclear. 4. The major effect of aerosols is attributed to global dimming by direct reduction of the solar radiation and increased reflection by clouds. Due to aerosols acting as cloud condensation nuclei (CNN), more clouds are formed existing of smaller droplets and with increased lifetime in the atmosphere resulting in the cloud albedo effect und the cloud lifetime effect.

9 Conversion of Carbon during Combustion and consecutive Partitioning of VOC C o m b u s t i o n Pyrolysis & Gasification I Flame C h i m n e y Atmosphere t Char CO, H 2, VOC VOC VOC C x H y O z Biomass O 2 =0 COC prim Tar >700 C COC sec Tar C brown in PM 10 local lack of O 2 > 800 C PAH tert Tar Soot BC in PM 10 H 2

10 Conversion of Carbon during Combustion and consecutive Partitioning of VOC C h i m n e y Atmosphere t 0 Atmosphere t VOC α = 30% CH 4 VOC 70% NMVOC γ =24% 66% ε = 34% NCNMVOC 0 COC 1 δ δ NCNMVOC SOA * POA C brown in PM 10 COC Soot BC in PM 10 All data are preliminary indicative values from a limited number of measurements. The conversion factors can vary in broad ranges due to varying combustion parameters. [Nussbaumer, T.; Boogen, N., SFOE, Berne 2010 (in press)] * m(soa) = f d m(ncnmvoc 0 ) f = 1.6±0.2 for urban aerosol f = 2.1±0.2 for non-urban aerosol f = (2.4) for wood smoke [Turpin, B.; Lim, J., Aerosol Science and Technology 35: (2001)]

11 Contribution of biomass to BC and Brown carbon? COC = 0 for near-complete combustion COC = 1 to 10 x (soot + salt) from incomplete combustion [Johansson et al., World Bioenergy 2008]

12 PM [mg/mj] based on LHV Solid Particles on hot filter: SP Particles in Dilution Tunnel: DT Solid Particles + Condensables: SPC Stove 1 Stove 2 DT/SP SPC/SP Text SP Tech. SWE SWI

13 Effect of biomass aerosols on climate change 1. If Biomass contributes to approx. 64% to BC [Bond 2009] but presumably more than 64% (close to 100%) to Brown carbon, > the direct effects of BC and Brown carbon are close to 0 or slightly warming acc. to IPCC > while it is might be significantly warming acc. to Bond* 2. The cloud albedo effect and the cloud lifetime effect are dominant for the total effect of aerosols and hence more relevant than direct heating and cooling by BC and Brown carbon. Since BC and brown carbon act as CCN**, the net effect of aerosols from biomass combustion by interpretation of the IPCC data is considered to be significant cooling (nevertheless not supposing the conclusion, that PM should be emitted for climate reasons). *It is important to notice that global effects of BC and Brown carbon from biomass combustion are dominated by open burning. **e.g. Leaitch, W, Lohmann, U. et al.: Cloud albedo increase from carbonaceous aerosol, Atmos. Chem. Phys. Discuss., 10, , 2010

14 1. Flue gases of biomass combustion contain a) salts, soot, and condensable organic compounds (COC) = primary aerosols as salts, black carbon, and brown carbon b) VOC, partitioning into remaining VOC and SOA 2. Black carbon is relevant for health and global warming and hence needs to be reduced by high priority (offering the chance for fast temporarily reduction of global warming, i.e. < 20 years) 3. Brown carbon is most relevant for health, while its contribution to global warming or cooling is uncertain / contradictory; in addition the effect of coating is unclear Conclusions 4. Salts exhibit smaller impact on health and cool the earth if available in pure form, while the effect of coating and interaction is uncertain 5. Reduction of Proudcts from Incomplete Combustion (Soot, COC, and VOC) is of 1. priority, reduction of salts is important too but 2. priority

15 Acknowledgments Swiss Federal Office of Environment (BAFU) Swiss Federal Office for Energy (BfE)