International Specialty Conference: Leapfrogging Opportunities for Air Quality Improvement

Transcription

1 International Specialty Conference: Leapfrogging Opportunities for Air Quality Improvement Identification of agricultural biomass burning impacting on Beijing air quality and direct observation of aged smoke aerosol particles Weijun Li (Shandong University); Longyi Shao (China University of Mining and Technology, Beijing); Peter R. Buseck (Arizona State University) May, 2010, Xi an China Hazy day Mountain Tai 04/19/2010 Clear day 04/26/2010

2 Outline 1. Climate effect of aerosols 2. Regional haze episodes 3. Experimental method 4. Results of individual aerosol particle analysis 5. Conclusions

3 1 Climate effect of aerosols Sources of soot, their radiation Globally, the annual emissions of soot (BC) Open biomass burning, 40% Biofuel, 20% Fossil-fuel (diesel and coal), 40% soot particles are the second most significant component of global warming after CO 2. Ramanathan and Carmichael, 2008 (Nature Geosci) Such mixing enhances the absorption of BC in troposphere Jacobson, 2001 (Nature). Many climate models ignore the internally mixed states of BC with sulfates. Ramanathan and Carmichael, 2008 (Nature Geosci)

4 1. Climate effect of aerosols BC distribution and its climate effects BC concentration BC heating atmosphere BC cooling ground North China Highest BC concentration Disturbing ground and air temperature Ramanathan and Carmichael, 2008 (Nature Geosci)

5 2 Regional haze episodes Aerosol Optical Depth at 550 nm over northern China The higher AOD value represents the more aerosols within a column; this translates to lower visibility within that column. Sources: AERONET data

6 2 Regional haze episodes Wildfire map from MODIS data 10 days 10 days 06/10-06/21/ /21-06/30/2007 What s different between two maps? Fire maps from the Moderate Resolution Imaging Spectroradiometer (MODIS) ( The open biomass burning mainly took place in Hebei, Shandong, Jiangsu, and Anhui provinces.

7 2 Regional haze episodes Scientific questions 1. Was air quality of Beijing influenced by biomass burning? Answer this question by aerosol particle analysis Element K is a good tracer of biomass burning emission 2. What are characteristics of biomass burning aerosol particles in regional hazes? What mixing state of biomass burning aerosol was dominant in Beijing air (transmission electron microscopy) Li and Shao, 2009, JGR; Li and Shao, 2009, ACP; Li and shao,

8 2 Regional haze episodes Mass concentration of pollutants Haze-i Haze-ii Six samples were collected during haze-i episodes Five samples were collected during haze-ii episodes Data from Beijing Environmental Protection Bureau

9 2 Regional haze episodes Hazy day (example) June 11th 2007 June 11th 2007 PM10: 222 SO2: 39 NO2: 68.8 Beijing 2 km Photos by WJL Gray sky Low visibility (1-5 km) High pollutant's loading Source: MODIS image

10 3 Experimental method Experimental method 3mm Environmental TEM Single particle sampler

11 3 Experimental method Aerosol particles on TEM grid Centre Periphery Five areas of each sample were chosen and observed by TEM

12 4 Results Size distributions of individual aerosol particles 2.1 µm 1066 haze particles 476 K- and S-rich particles 0.7 µm Haze particle types include mineral, complex secondary (Ca-S, K-, and S-rich), organic, soot, fly ash, and metal (Fe-rich and Zn-bearing). Li and Shao, 2009 (JGR and ACP)

13 4 Results Aerosol particles in haze-i and haze-ii More complex Morphologies Complex

14 4 Results K-rich particle Diffraction EDX spectra K 2 SO 4 KNO 3

15 4 Results Tar ball in haze-i Elemental compositions of tar ball include C, O and minor N Few particles in the samples of type-1 haze

16 4 Results S-rich particle Diffraction and EDX data (NH 4 ) 2 SO 4 Internally mixed minor potassium salts

17 4 Results Particlesin haze-i and haze-ii KNO 3 and K 2 SO particles 128 particles Comparisons between type-1 and type-2 haze indicate biomass burning particles impacted the air quality during June, Aged ABB aerosol particles commonly occurred in Beijing air.

18 4 Results Internally mixed particles in hazes Most soot and organic particles were internally mixed with K- and S-rich particles. Implications: 1. Hygroscopic properties 2. Optical properties of aerosol particle The climate models should consider the mixtures in hazes

19 4 Results Sulfate Structure of soot particle soot Organic Onion-like structure of curved and disordered graphitic layers.

20 Effects of ABB emissions on the brown hazes Whenever RH is elevated, its importance on AOD is substantially amplified because the aerosols are hygroscopic (Bian et al., 2009). AOD Haze- 1> haze-2 Aerosol vs. AOD PM concentration Aerosol components Mixing state Hygroscopic growth Soot internally mixed with sulfates and Hygroscopic growth of aerosols in the hazes were considered particularly to increase AOD in haze-1.

21 5 Conclusions Conclusions Agricultural biomass burning influenced air quality of Beijing in a concentrated time. Most soot and organic particles are internally mixed with K- and S-rich particles in hazes. Hygroscopic growth of aerosols and soot particles from ABB contribute to regional AOD.

22 Thank you for your attention QUESTION?