Dust and its Role in Tropospheric Chemistry A Modelers View

Transcription

1 Dust and its Role in Tropospheric Chemistry A Modelers View Gregory R. Carmichael, Vicki Grassian, Kim Prather 2, Bhupesh Adhikary, Courtney Hatch Center for Global and Regional Environmental Research University of Iowa, Iowa City, IA USA 2 -University of California, San Diego

2 Personal Original Motivation: What roles do chemical interactions play in the correlations between dust and ozone (and other species) at mountain sites in East Asia? Kotamarthi, V. and G. R. Carmichael, Long Range Transport of Dust in Asia, Tellus, Zhang, Y. Sunwoo, V. Kotamarthi and G. Carmichael, Photochemical oxidant processes in the presence of dust: an evaluation of the impact of dust on ozone, nitrate and free radical formation J. Applied Meteorology, * Dentener, F., Y. Zhang, G. Carmichael, P. Crutzen and J. Lebiesueld, The role of Mineral Aerosol as a Reactive Surface in the Global Trophosphere, J. Geophy. Res., 1996 Happo Japan

3 Mineral Aerosols Perturb Atmospheric Chemistry in Several Important Ways Mineral Aerosol Perturb Trace Gas Cycles in Many Ways Increase SO 2 to sulfate conversion rates. Increase the importance of dry deposition. Decrease the lifetime of SO x, NO y and VOC? Control the partitioning of semi-volatile species (e.g., HNO 3 ). Influence precipitation ph. Provide reaction channels which may: recycle No x ; produce particulate nitrate; make longer chain VOCs; provide radical sources; and indirectly/directly Perturb O 3 ; and alter water uptake. Alter photolysis rates. Alter aerosol optical aerosol properties and CCN activity. Models Laboratory Field Experiments What progress have we made in quantifying these effects?

4 Framework for Analyzing Chemistry/Aerosol Interactions: Model (STEM+TUV) + Laboratory Studies + Field Experiment TUV TOP 80km Overtop O 3 = O 3 (Dobson) below STEM top height STEM TOP 15km Inputs from STEM 3-D field Ice cloud Water cloud Surface reflection absorption by gas-phase species O 3, SO 2 and NO 2 EP/TOMS Total Ozone (Dobson) Sea Salt Heterogeneous rxns on dust for NO x, O 3, SO 2, HNO 3 Dust Black Carbon Organic Carbon Sulfate Other PM2.5 and Other PM10 Outputs: Effects on Photolysis rates, Photo chem., biogeochem cycle, aerosol comp., optical prop., CCN

5 Experimental Techniques and Methods Developed at the University of Iowa for the Study of Mineral Dust Aerosol Lead by Vicki Grassian Water Uptake Measurements ATR-FTIR Quarts Crystal Microbalance MAARS Hygroscopic Growth Measurements CCN Activity Heterogeneous Reaction Kinetics MAARS Future goals Knudsen Cell Measurements Aerosol Reaction Chamber Single Particle SEM measurements (in collaboration with PNNL) Optical Properties MAARS (Infrared Extinction Measurements) Aerosol Reaction Chamber (Broadband Extinction measurements from the UV to IR) Light Scattering (UV/Vis)

6 Improving predictions in mass distributions due to a significant community of dust modelers working at various scales, with growing number of operational forecasting efforts, and closer evaluation efforts through use of growing observing systems

7 Aerosols in the East Asia Environment Have a Profound Impact on Resulting Secondary Pollution Formation Through Radiative Feedbacks Observed NORMAL NOAOD CLEARSKY Flight Altitude O 3 (ppbv) Altitude (m) TIME (GMT) 0

8 Julian Day (GMT) C-130 Flight 8 encountered aged dust. - Dust significantly increased the super-micron sulfate and nitrate concentrations. Extracted model results along trajectory B illustrating the dust aging process Fine Ions (ug/std m 3 ) Coarse Ions (ug/std m 3 ) Calcium Ammonium Nitrate Sulfate Julian Day (GMT) 8 Calcium Ammonium Coarse Nitrate Sulfate Fine We ve learned much from the lab studies in terms of variability of reaction rates via surface, co-species effects etc., much for dry systems, - less in the presence of water

9 Mineral Aerosol Chemistry Aerosol Reaction Chamber: N 2 O 5 Hydrolysis Composition and RH dependences are important not reflected (well0 in current models P.K. Mogili et al., Atmospheric Environment, 40, , 2006

10 ATOFMS Area Ratios for Coarse Sea Salt Particles Simulated Coarse NO - 3 (ug/std m 3 ) without Dust and the Difference between with and without Dust ATOFMS Coarse Area Ratio 81/108 ATOFMS Coarse Area Ratio 81/165 Simulated Processed Coarse Cl Julian Day Simulated Coarse NO3 without Dust Simulated Coarse NO3 Difference ATOFMS Sea Salt Percentage ATOFMS Dust Percentage Julian Day (GMT) Tang et al., JGR, Simulated Processed Cl (ug/std m 3 ) on Coarse Sea salt ATOFMS Measured Percentages of Coarse Nitrate Contained in Sea Salt and Dust A Modeling Challenge is to Better Utilize the Advances in Measurements How to utilize the statistics based on number when models currently are based on mass? We have a new NSF project (Kim, Vicki, myself) project looking at acid chemistry on dust/ sea salt systems.

11 Dust Impacts on Ozone and Photochemistry C-130 April 11 What additional measurements can be used to test this prediction? O 3 (ppbv) Observed NORMAL NODUST FULL Flight Altitude Altitude (m) TIME (GMT) Large Ozone Signal in the Model (γ = 5 x 10-5 ) 0

12 Heterogeneous O 3 Chemistry on Dust O 3 Decomposition as f(rh) on α-fe 2 O 3 Little progress has been made in reducing uncertainty in the global/regional importance of this reaction pathway. RH Decreases Reactivity:Bare α-fe 2 O 3 vs Water Covered Sites even at high RH (Mogili et al JPCA) P.K. Mogili et al., J. Phys. Chem. A, 110, , 2006

13 Chemistry on Dust has Implications for Radiative Forcing

14 The Effect on Calculated AOD and Forcing When Using Observational Parameterizations for Optical Properties can be Large Especially in Dusty Environments. A priori Constrained Bates et al., ACP, 2006

15 Dust Hygroscopic Growth CaCO 3 (Fresh Dust) vs. Ca(NO 3 ) 2 ( Aged Dust) Growth factor = D p /D 0 D 0 = 100 nm Ca(NO 3 ) 2 CaCO 3 E.R. Gibson et al., Geophys. Res. Lett., 33, L13811, doi: /2006gl

16 Dust CCN Activity 200 nm CaCO 3 vs. Ca(NO 3 ) 2 Ca(NO 3 ) 2 is already 100% activated at the lowest attainable supersaturations CaCO 3 in 0.01 wt% Ca(NO 3 ) 2 solution critical supersaturation = 0.3% SS CaCO 3 in 0.05 wt% Ca(NO 3 ) 2 solution critical supersaturation = 0.2% SS Partial processing results in partial increase in CCN activity CaCO 3 Ca(NO 3 ) 2 HNO3 N 2 O 5 HNO 3 N 2 O 5 E.R. Gibson et al., GRL, In Press, May 2007

17 PACDEX (The Pacific Dust Experiment) 2007 April/May Using the NSF G5 Aircraft Ramanathan, J Stith et al. Measurement of interaction of dust episode and pollution with clouds (warm and cold) Document radiatively important regions of the plume Black carbon and clouds are major climate drivers, yet poorly understood, especially in this region Use results to improve NCAR and other models

18 AOD AOD Dust is a significant component of many environments -- and for many time periods Model (550nm) versus Aeronet (500nm) Aerosol Optical Depth at KANPUR AERONET AOT_500 STEM Total AOD Model Predicted Total AOD at KANPUR /1 10/1 10/31 11/30 12/30 1/29 2/28 3/30 4/29 5/29 6/28 7/28 8/ Date ( ) SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG Kanpur AOD Results Adhikary et al., JGR, 2007

19 Dust is a significant component of many environments -- and for many periods. Data Assimilated Average ( ) Aerosol Optical Depth Sulfate BC OC SSF SSC DUSTF DUSTC MODIS Tehran Karachi Delhi Mumbai Kolkata Dhaka Bangkok Jakarta Shenzhen Beijing Manila Shanghai Seol Hanimaadhu Gosan Bukit Kototabang ABC-Pyramid Waligaon Location AOD (unitless)

20 Closing Comments Significant advances have occurred in lab, field, modeling elements of dust. On the lab. side relatively little information on heterogeneous photochemistry. Models are including more details with respect to dust but modest advances have been made in quantifying the role of chemistry on dust as it relates to sulfur, nitrogen, oxidant cycle. Models need improvements in modeling dust composition and size distributions. Models need to better reflect current knowledge of the chemistry involving dust and its impact on optical properties. Exciting time for investigating the feedbacks between dustchemisty-climate system. A closer integration of the models and observations Formal data assimilation techniques using expanding observations are encouraged!

21 Central Asia is a Region of Growing Interest A New ABC Site is being Established. Collaborators Welcomed! Trajectories of long range transport at height 3500 m over sea level

22

23 Closing Thoughts 15 years of studying mineral aerosol as a reactive surface Advances have taken place in models, fundamental laboratory, and in the field A look at how far we have come, And where we still have gaps Advances will still require a closer integration of models and field

24