Presentation on theme: "Atmospheric Aerosol From the Source to the Receptor Insights from the Pittsburgh Supersite Spyros Pandis, Allen Robinson, and Cliff Davidson Department."— Presentation transcript:
Atmospheric Aerosol From the Source to the Receptor Insights from the Pittsburgh Supersite Spyros Pandis, Allen Robinson, and Cliff Davidson Department of Engineering and Public Policy Carnegie Mellon University
Fine PM Composition PM 2.5 ( g/m 3 ) Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 2001 2002 PM 2.5 mass
PM 2.5 Mass Balance (July and August 2001) PM 2.5 (µg/m 3 ) Organics Sulfate Nitrate Ammonium EC Crustal 1 8 15 22 29 5 12 19 26 July August
Mass Balance Closure – July 2001 0 10 20 30 40 50 60 Water Crustal NO3 SO4 NH4 EC OC*1.8 FRM PM 2.5 ( g m -3 ) 1 4 7 10 13 16 19 22 25 28 31 Date (July 2001) Good mass balance was achieved for the winter months
July 26, 2002 (16.2 g m -3 ) Increase as winds shift direction Decrease after a front passed, wind speeds decreased, and some rain fell Continuous Sulfate Measurements and Long Range Transport 24:00 PM 2.5 Sulfate ( g/m 3 ) Hour (EST) 0:00 EST 12:00 EST
The Source-Receptor Challenge: Interactions between Fine PM and Their Precursors NO x emissions SO 2 emissions VOC emissions NH 3 emissions Primary Organic emissions Primary Inorganic PM emissions Crustal Ammonium EC Nitrate Sulfate Organics PM 2.5 Composition during the Winter
Ammonium Nitrate Formation The formation of ammonium nitrate requires Nitric acid (major sources of NOx in the US are transportation and power plants) Free ammonia (ammonia not taken up by sulfate) The formation reaction is favored at: Low temperatures (night, winter, fall, spring) High relative humidity Hypothesis: A significant fraction of the sulfate reduced will be replaced by nitrate when SO 2 emissions are reduced.
Modeling Nitrate Partitioning Aerosol Nitrate ( g m -3 ) Date Summer Winter
Effect of Sulfate Concentration Changes on Inorganic PM 2.5 Inorganic PM 2.5 ( g m -3 ) Sulfate Reduction
Reductions of Sulfuric and Nitric Acid (Pittsburgh, July 2001) 0102030 0 10 20 30 Sulfate Reduction (%) Inorganic PM 2.5 Reduction (%) Same Nitric Acid -50% Nitric Acid
Reducing Inorganic PM2.5 Using an observation-based model: Controls of SO 2 will reduce sulfate and PM 2.5 in all seasons. A fraction of the now existing sulfate will be replaced by nitrate. The lifetime of nitrate will increase during the summer because it will move from the gas to the aerosol phase For Pittsburgh, ammonia controls in all seasons can minimize the replacement of sulfate by nitrate. For Pittsburgh, NOx controls will help reduce the nitrate during the winter but they will have a small effect during the summer.
Nucleation Frequency 20012002 Fraction of Days With Nucleation Significant fraction of days (30%) Most prevalent in spring, fall
Aerosol Number and Mass Pittsburgh, PA 2001-2002 Aerosol Mass (μg/m 3 ) Number (#/cm 3 ) 10x10 4 20x10 4 Negative correlation related to nucleation activity PM 2.5 ( g m -3 )
Composition of 10-60 nm Particles (Jimenez, U. Colorado and Worsnop, Aerodyne) Particle Size (nm) 10 100 500 00:0006:0012:0018:0024:00 50% 0% 100% Mass Fraction 10-60 nm Nitrate Ammonium Sulfate Organics Mass Fraction (10-60 nm Particles) Aerosol Mass Spectrometer* *Zhang & Jimenez (Univ. Colorado-Boulder)
Nucleation Model Evaluation (July 27, 2001) Measured Predicted
Nucleation and Ultrafine Particles The model was successful in reproducing the observed behavior (nucleation or lack of) in all simulated dates in July (10) and January (10) Strong evidence that the nuclei are sulfuric acid/ammonium/water clusters Growth with the help of organics Discrepancies in the nucleation rates the model tends to predict higher rates Ammonia appears to be the controlling reactant ! Small to modest reductions of ammonia can turn off the nucleation in the area especially during the summer
PMCAMx+ Modeling Domain July 12, 2001 July 17, 2001 PM 2.5 Sulfate 36x36 km grid, 14 levels up to 6 km 10 aerosol sections, 13 aerosol species 20 million differential equations 8 CPU hours on a PC per simulation day (EQUIlibrium module)
SOA Simulation (July 2001) AnthropogenicBiogenic
PMCAMx+ Evaluation in Pittsburgh PM 2.5 Sulfate Nitrate Ammonium OM EC
Predicted vs. Estimated in Pittsburgh (Primary and Secondary OA) Predicted [ g/m 3 ] Estimated [ g/m 3 ] EC Tracer Method (Cabada et al., 2003)
PM 2.5 Response (%) to 30% SO 2 Emission Reduction July 18, 2001 Concentration Change ( g m -3 ) Percent Change
Conclusions Water is retained in the FRM filters during the days with high sulfate and acidity The water can be estimated with a thermodynamic model and it will decrease as sulfate decreases Large regional contributions for both sulfate and organics Development of observation based model for the substitution of sulfate by nitrate (requires nitric acid and ammonia measurements) SO2 reductions will reduce sulfate and PM2.5 but nitrate will also increase in all seasons Ammonia reductions can prevent the nitrate increase NOx reductions can help during the winter Organic aerosol sources: Roughly 30-40% of the organic PM is secondary during the summer (higher in worst days) and around 10% during the winter. Evidence for significant primary biogenic PM during the summer (around 30%) Transportation and biomass burning are the other significant sources in the area
Conclusions (continued) New technologies (Single Particle Mass Spectrometry, semi-continuous metal measurements) allow the fingerprinting of point sources. Frequent nucleation events (around 100 per year) At low PM concentrations Sunlight Evidence for regional scale (100-300 km) Sulfuric acid/ammonia/water nuclei Ammonia appears to be the limiting reactant for most events Supersite data together with the results from other studies and networks will allow us to evaluate our understanding of atmospheric PM in the US First results of PMCAMx for summer 2001 are encouraging Consistency between 3D CTM results and observation based models for nitrate and SOA.
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