Recent Science on Aerosols in Asia. Yutaka Kondo

Transcription

1 Recent Science on Aerosols in Asia Yutaka Kondo Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan Translating Co-benefits Resasrch into Action in Asia: Science, Models, Projects, and IGES, Hayama, Kanagawa 18 February 2013 This work was supported by and the global environment research fund of the Japanese Ministry of the Environment (A-1101) and the Ministry of Education, Culture, Sports, Science, and Technology (MEXT).

2 Contents of this presentation International assessments of the effects of black-carbon reduction Current understanding on the radiative forcing (climate effect) of BC and its uncertainties New directions for future research and suggestions for policy makers

3 Sources of black carbon (BC)(Bounding BC, JGR, 2013) BC is emitted by incomplete combustion of fossil fuel and biomass Non-spherical carbon particles with diameters less than 1 μm Strongly absorbs solar visible radiation and heats the atmosphere Deposit on snow and ice and contributes to the warming of the Arctic

4 Climate models as a tool of estimating climate forcing of BC Radiative forcing (RF) [W m -2 ] The change in the net vertical irradiance at the tropopause caused by a particular constituent. λ = ΔT /RF : Climate sensitivity [K/(W m -2 )] ΔT = λ RF RF is linked with surface temperature

5 Direct radiative forcing of BC estimated by models b abs = MAC M BC : absorption coefficient (m -1 ) MAC: mass absorption cross section (m 2 g -1 ) M BC : BC mass concentration (g m -3 ) AAOD = column b abs dz = MAC column M BC dz DRF = AFE (absorption forcing efficiency) AAOD

6 AAOD: AERONET and AeroCom models AERONET: BC AAOD = AAOD dust AAOD AeroCom models underestimate BC AAOD Observed AAOD/Calculated AAOD = 2.9 (global average) BC AAOD (model) = (global average) Calculated BC DRF is multiplied by the scaling factor (regional)

7 Adjustments to Climate forcing of BC scaled with AERONET Adjustments are large in south Asia, East Asia, and Africa Adjustments are mainly ascribed to the underestimate of BC emissions

8 Regional BC AAOD scaling and contributions Models largely underestimate burden (BB and energy-related) The effect of MAC is moderate

9 BC RF by Bounding BC BC forcing is the second most important individual climate forcing agent Total BC cloud effect is positive Cooling effect of co-emitted species is potentially large but highly uncertain

10 Causes of uncertainties of BC RF by Bounding BC and AEROCOM 1) Bounding BC (scaling by AAOD) Uncertainty of the observed AAOD is large All AAOD in fine mode is attributed to BC Dust in fine mode and brown carbon can contribute 2) AEROCOM models (bottom up estimate) AAOD is not constrained by global observations Emissions can be underestimated The discrepancy is unresolved yet There are strong needs to improved understanding of RF of aerosols: Emission, transport, optical properties

11 Removal of BC by precipitation (Moteki, Kondo, Oshima, et al., 2012) Category: Transport, Transport efficiency of BC (TE) decreased rapidly at 2 km Regional scale model reproduced the TE Some GCM did not reproduce M BC GCM results vs observation Coated BC is taken up by clouds and removed by precipitation Models need to represent mixing state and represent the distribution of precipitation Observed TE is a key parameter to diagnose the performance of models

12 Long term BC observations to validate models (Kondo, Matsui, et al., 2012) Category: Emission and Transport BC emission and sites Improve understanding on seasonal and altitude variations of BC Validate BC emissions in East Asia (China) Uncertainties of the current inventory is abut 200% We estimated BC emissions from China to within 40% COSMOS

13 BC observation network in Asia Continuous BC in East Asia Miyun Beijing Dalian Gosan Fukue Hedo Lulin (2.8 km) Happo (1.8 km) Echizen-Misaki International network BC observation in East Asia is being established (Tsinghua U, Dalian IT, Taiwan NU, Seoul NU) We plan cooperation with South Asia and SEA

14 Microphysical properties of BC Category: Optical properties 1. Absorption cross section of BC Spherules consisting BC < 50 nm Classical electromagnetic theory may fail (wavelength >> 50 nm) More consistent physical theory is needed. 2. Mixing state of BC Amplification of light absorption of atmospheric BC Needs further quantification Location of BC core inside aerosol particle New technology is being developed or

15 Needs for futures studies to improved RF of BC Uncertainties are still large. Each element for RF need to be further elucidated BC DRF = E L MAC AFE Emission: Validate emissions by surface measurements L: Wet deposition (rain), transport efficiency (aircraft and high altitude sites) MAC: Mixing state, refractive index, brown carbon In-situ closure studies need to be designed Evaluation of the method of remote sensing in deriving AAOD AERONET and satellite data Arctic: Wet deposition of BC by snow and rain GRENE project We expect large advances in these areas in a few years

16 Considerations for identifying important mitigation options 1. Potential to reduce net climate forcing The radiative forcing contributions from species (gases and aerosols) co-emitted with BC are highly uncertain but expected to be negative overall. The effect of regulations of BC emissions from vehicular sources is least uncertain (e.g., low OC/BC and low sulfur/bc ratios) and thus should be encouraged. 2. Potential to benefit sensitive regions such as the Arctic and high mountain areas Deposition of BC on snow/ice reduces albedo, contributing to the warming of the Arctic and changes in hydrological cycles. 3. Availability of technologies and management practices 4. Health benefits BC (µg m -3 ) Beijing 2007 Tokyo 2007 Guangzhou 2006 Bangkok (wet) 2007 Bangkok (dry) :00 6:00 12:00 18:00 0:00 Local Time