BIOMASS BURNING CONTRIBUTION TO CARBONACEOUS AEROSOLS IN THE WESTERN U.S. MOUNTAIN RANGES

Transcription

1 BIOMASS BURNING CONTRIBUTION TO CARBONACEOUS AEROSOLS IN THE WESTERN U.S. MOUNTAIN RANGES Yuhao Mao, Qinbin Li, Li Zhang, Dan Chen, Kuo-Nan Liou Dept. of Atmospheric & Oceanic Sciences, UCLA UCLA-JPL Joint Institute For Regional Earth System Science & Engineering (JIFRESSE) Chen Yang, Yufang Jin, James Randerson Dept. of Earth System Science, UC Irvine The 5 th International GEOS Chem Meeting, May 2-5, 2011 Harvard University

2 Wildfires are an Important Source to BC & OC in the Western U.S. (Spracklen et al., 2007, 2009; Park et al., 2007; Jaffe et al., 2008) Wildfire frequency and fire season length have been increasing in the Western U.S. because earlier spring and warmer temperatures in spring and summer (Westerling et al, 2006) Under a warming climate, annual mean burned area in the western U.S. projected to increase by 54% by the 2050s relative to the present (Spracklen et al., 2009).

3 IMPROVE Observations of Surface BC & OC (Interagency Monitoring of Protected Visual Environments) Established in 1985 for the protection of visibility in Class I remote areas BC & OC measurements Thermal Optical Reflectance (TOR) combustion method Measurement frequency: Daily average Every 3 days 50 N 45 N 40 N Height/m sites in the western U.S., many are mountainous sites N N 125 W 120 W 115 W 110 W 105 W 100 W 3 0

4 Surface BC & OC in the Western U.S. Model surface BC reproduces the observed day-to-day and synoptic variabilities at sites near or downwind of urban areas. This implies that anthropogenic emissions of BC in the model are reasonable. Surface OC concentrations at these sites are underestimated much of the year especially during summer and fall.

5 Surface BC at Mountainous Sites Biased low by > 2 X during the Summer and Fall Fire Season 1-2 km (30 sites) The discrepancies are evident not only in the absolute surface BC levels but also in the timing of the enhancements due to fire emissions. 2-3 km (18 sites) Uncertainties in both the estimates of fire emissions of BC and the (lack of) detection of (small, agricultural) burnings are likely partial causes for these discrepancies.

6 High BC Concentrations are Strongly Correlated with Enhanced K and K/S ratios Potassium (K) concentration and K/S (sulfur) ratio increased significantly during the fire episodes hence are tracers of fire influence (Tanner et al, 2001) Strong BC-soil correlations suggest dominant anthropogenic influence.

7 Improved Temporal Variation in Biomass Burning Emissions (synoptic variability, diurnal cycle) had limited impact on simulated surface BC Largest effects seen at 1-2 km sites in source regions with strong emissions. 1-2 km (30 sites)

8 Nested Simulation Shows Some Improvements in Surface BC in the Western U.S. Sites at 1-2 km see largest improvements during the fire season. <1 km (18 sites) 1-2 km (30 sites) 2-3 km (18 sites) 3-4 km (3 sites)

9 Surface OC Underestimated during Apr.-Nov. Nested simulation shows improvements at low-altitude sites Improved boundary layer simulation (mixing) in the nested simulation? <1 km (18 sites) 1-2 km (30 sites) 2-3 km (18 sites) 3-4 km (3 sites)

10 A Previous GEOS-Chem Modeling Study (Park et al., 2003) Showed Good Agreement with IMPROVE Data (r 2 > 0.8) GEOS-3 GOES-3 vs. GEOS-4 reanalyses: differing moist process parameterizations and boundary layer schemes IMPROVE GEOS-3 GEOS-4 Large differences between model results from simulations driven by GEOS-3 vs. GEOS-4! Much higher surface BC concentrations in the former! Are the results with GEOS-3 better?

11 PBL Height in GEOS 13:00 LST GEOS-4, GEOS-3 vs. NARR Aug Sept The unusually shallow boundary layer in GEOS-3 resulted in artificially high surface BC concentrations. This GEOS-4, implies GEOS-5 that biomass vs. NARRburning emissions of BC were likely significantly underestimated in Park et al. (2003) as well. (U.S. fossil fuel emissions of BC were reasonable.) Aug Sept. 2006

12 GEOS-3 is too Dry over the Western U.S. Aug GEOS-3 GEOS-4 CMAP GPCP

13 Summary Biomass burning was the dominant source of surface BC in the western U.S. mountain ranges during the summer and fall fire season. Model surface BC concentrations in the western U.S. mountain ranges were underestimated by more than a factor of two. These large discrepancies were likely due to the current BC biomass burning emissions in the model underestimated in the western N. America. The use of biomass burning emissions with diurnal cycle, synoptic variability, and plume injection had relatively small impact on the simulated surface BC concentrations in the western U.S. N. America nested simulation showed slight Improvement on model surface BC over the western U.S. GEOS-Chem driven by GEOS-5 data provided the best agreement with IMPROVE observations of BC. Because of the unusually low PBL heights and weak precipitation in the GEOS-3, the biomass burning contribution to surface BC concentrations in the U.S. likely was underestimated in a previous study [Park et al., 2003]. Model underestimated surface OC concentrations during Apr.-Nov. What are the possible explanations to these large discrepancies, the uncertainties in the SOA simulations or the underestimated emissions in the model? Manuscript submitted to ACPD, Mao et al. [2011]

14 Motivation (IPCC, 2007)

15 Model Description Global (2 2.5 ) GEOS-Chem v GEOS-3,4, 5 met. fields 30 or 47 vertical layers Offline BC & OC simulations for 2006 N. America nested simulations (0.5 o 0.67 o ) (10 70 o N, o W) GEOS-Chem v GEOS-5 met. fields 30/47 vertical layers Boundary condition from global 2 o 2.5 o simulation updated every 3 hours Full chemistry with SOA for 2006 Offline BC & OC simulations for 2004 Anthropogenic Emission ( fossil fuel and biofuel ) Global: Bond et al. [2007] Asia: David Streets [2006] N. America: Cooke et al [1999] monthly mean inventory Biomass Burning Emissions GFEDv2 & v3 monthly, 8-day, 3-h for 2004 & 2006 (Randerson et al.) Biogenic Emissions: Guenther et al. [1995, 2006] 15

16 Linear Increase of Biomass Burning BC Contributions with increasing Fire Emissions 1-2 km (16 sites) 2-3 km

17 Motivation BC: Incomplete combustion of carbonaceous fuels 2004 NARSTO Assessment Fossil fuel combustion (40%); Biomass burning (40%); Biofuels (20%) (Bond et al., 2004) OC: Primary & Secondary Fossil fuel, Biomass burning, Biofuel, Biogenic. Organic carbon constitutes 10-70% of aerosol mass at surface. Courtesy of Colette Heald

18 OC is underestimated in current models Secondary production of OC aerosols is considerably underestimated in current models, both in surface air and in the free troposphere. (Heald et al., 2005, 2006) (Volkamer et al., 2006)

19 GEOS-4 is too Wet over the Western U.S. Sep GEOS-5 GEOS-4 CMAP GPCP

20 GFED Monthly Mean Total C in the Western U.S. Biomass mass buring C(Tg) o N, o W Year GFED2 GFED3 Biomass mass buring C(Tg) o N, o W GFED2 GFED3 20 Jan Apr Jul Oct 2006 Time

21 GFEDv3 vs. v2: Higher BC Emissions in August but Lower in September 2006; very different spatial distributions GFED v3, Aug GFED v2, Aug GFED v3, Sept GFED v2, Sept. 2006

22 BB tracers K Ratio of fire episode to nonepisode concentrations by element or species, May Species concentrations during fire episode in spring (MAM) 1998 [Tanner et al, 2001] 22

23 Improved Temporal Variation of Biomass Burning Emissions Global Fire Emissions Database (GFEDv2) biomass burning emissions Mean diurnal cycle based upon active fire observations; peak burning occurs typically in the afternoon. Synoptic variability based upon the Initial Spread Index (ISI, depends on T, RH, wind, precip.); Wildfires are influenced by synoptic weather. Chen et al. [ACP, 2009]

24 Vertical Injection Height of Biomass Burning Emissions MISR smoke plume heights (brown circles) & GFED emissions Vertical profiles for releasing fire emissions Chen et al. [ACP, 2009]

25 Relative Contributions Altitude NA Asia BB Annual All (69) (78.99) (9.44) (9.85) All (88.38) (8.30) (1.95) DJF 2-3km (18) (79.43) (15.29) (2.49) 3-4km (3) (62.01) (28.14) (4.30) MAM All (78.27) (13.78) (5.94) 2-3km (71.29) (19.39) (6.43) 3-4km (63.16) (24.39) (8.04) JJA SON All (74.98) (10.37) (12.84) 1-2km (30) (73.51) (10.28) (14.43) All (75.85) (5.91) (16.56) 1-2km (72.62) (5.65) (19.96) 25