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EAS 4/8803: Experimental Methods in AQ

EAS 4/8803: Experimental Methods in AQ. Week 11: Air Quality Management (AQM) Clean Air Act (History, Objectives, NAAQS) Emissions and Atmospheric Trends (Links) Principal Measurement Techniques (NOx, CO, SO 2 ) Measurement of CO (Exp 5)

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EAS 4/8803: Experimental Methods in AQ

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  1. EAS 4/8803: Experimental Methods in AQ Week 11: Air Quality Management (AQM) Clean Air Act (History, Objectives, NAAQS) Emissions and Atmospheric Trends (Links) Principal Measurement Techniques (NOx, CO, SO2) Measurement of CO (Exp 5) NDIR Method (Interferences, Stability, DL, Precision, Accuracy) Controlling O3 and PM2.5 Principal Measurement Techniques (O3, PM2.5) Atmospheric Transport & Photochemistry (NOx vs VOC, SOA) Ambient Measurements and Trends (World, USA, GA) Measurement of O3 (Exp 6) UV Absorption (Interferences, Stability, DL, Precision, Accuracy) EAS 4/8803

  2. Tapered Element Oscillating Microbalance If PM of mass Dm deposit on piezoelectric quartz crystal, frequency changes by Df = Kq Q t cm with sensitivity Kq, aerosol mass flow Q, time t, and PM mass concentration cm EAS 4/8803

  3. TEOM Method If PM of mass Dm deposit on piezoelectric quartz crystal, frequency changes by Df = Kq Q t cm with sensitivity Kq, aerosol mass flow Q, time t, and PM mass concentration cm EAS 4/8803

  4. TEOM Setup and Operation • Reducing H2O Interference • Inclusion of Nafion dryer using TEOM’s exhaust (low p, dry) • as sheath flow. • Filter housing T-controlled • at 50 oC. EAS 4/8803

  5. 254 m agl 6 m agl Assessing Accuracy of PM2.5 Mass MeasurementsComparison of dry TEOM averages with dehydrated Teflon samples Williams Tower is ~20 km west of LaPorte, which is close to Ship Channel EAS 4/8803

  6. High Resolution vs Integrated [PM2.5]at LaPorte and Williams Tower Large [PM2.5] transients (spikes) at both sites: Chemistry or transport? Transients (changes in [PM2.5]) larger at WT, esp. at night. Averages of integrated samplers (8-24h) are very similar and follow a regional trend. EAS 4/8803

  7. Adding Photochemistry (O3) LP max [O3] on 08/30 is more than twice WT-[O3], which seems to follow a “rising tide”. Fast P(O3) at LP (<200 ppb/h): high precursor emissions (Alkenes, NOx) in Ship Channel. More regional influence from BB plume on 9/5 + 9/6: joint increase in [PM2.5]. EAS 4/8803

  8. Trend to higher WT-[PM2.5] mostly at night, similar to vertical gradients at Hendersonville, but note 20 km WT-LP distance! Average Diurnal Differences in [O3] and [PM2.5] WT-O3 levels are significantly higher at night and early mornings: Separation from nocturnal surface inversion; LP-O3 titration. LP-O3 higher at midday: >P(O3) from precursor mix and closer sources. EAS 4/8803

  9. Vertical Gradients of PM2.5 During SOS’99, 16 June - 22 July 1999, measurements near Nashville, TN, between 4 and 42 m agl showed positive vertical gradients for 60-70 % of all daytime, and 70-80 % of all nighttime samples of PM2.5 mass, SO4=, NO3-, and NH4+!! Direct emissions and/or secondary formation of fine PM aloft. Free Troposphere Source for PM2.5! EAS 4/8803

  10. Vertical Gradients of PM2.5 Free Troposphere Source for PM2.5! BL Dynamics Important Influence on Ground-Based AQ Monitoring !! EAS 4/8803

  11. Vertical Wind Profile: Advection Horizontal Transport Near logarithmic increase of WS and uniform WD within well-mixed BL. Clockwise rotation with height near BL top to merge with more geostrophic winds. Nighttime separation of layers with different wind speeds and directions. EAS 4/8803

  12. PM2.5 Wind Roses: Seasonal Differences Across GAIndications for Regional Advective Transport? Period 2001+ 02 MAY-OCT NOV-APR Aug’99 EAS 4/8803

  13. …Similarity to Daytime O3 Period 2001+ 02 MAY-OCT NOV-APR Aug’99 EAS 4/8803

  14. Summertime PM2.5 – Max(O3) Relationship Tighter correlation in July 2001. “Downwind” Griffin site offset to higher PM2.5 mass. August 99 in Atlanta was hotter, dryer, more polluted with O3-precursor species. EAS 4/8803

  15. Seasonal & Regional Comparison of PM2.5 Composition Summer Months Winter Months Regional Difference: Higher OM/OC and OC/EC at more rural site! Seasonal Difference: Lower OM/OC and (higher) OC/EC in winter. More SOA in August 99?More oxygenated POCs away from Atlanta? EAS 4/8803

  16. downwind Atlanta JST Griffin Photochemical ActivitySource – Receptor Considerations: O3/NOz as “OPE” Elevated regional O3 background reflected in regression’s intercept: higher in Aug 99! At JST higher intercept and slope during Aug ’99 (OPE= 4 vs 3): more efficient P(O3). OPE in air mass arriving at Griffin is likely larger given by upper and lower limits. Lower limit assumes 1st order loss of HNO3 due to surface deposition at k ≈ 0.22 h-1. Air mass transitions from VOC-limited to NOx-limited regime due to Biogenic HC. High photochemical activity P(O3) allows for high P(SOA): rural/urban gradient. EAS 4/8803

  17. Photochemical Processes Leading to O3 and PM An Assessment of Tropospheric Ozone Pollution, A North American Perspective, NARSTO, National Acad. Press, 2000. NOz SOA EAS 4/8803

  18. Ozone Isopleths Area of effective VOC control (most often highly populated areas) Constant [O3] NOx control effective(areas with high biogenics) Nitrogen Oxides (NOx) High [O3] Low [O3] Volatile Organic Compounds (VOC) EAS 4/8803

  19. O3 O2 hv NO2 HNO3 NO OH RO2 /HO2 RO,OH OH SOA & O3 Formationand Transport Fine PM, SOA PM, SO2, NOx Emissions Wind Deposition Rainout VOC Emissions O3, HNO3 PM EAS 4/8803

  20. Planetary Boundary Layer Dynamics PBL strongly influenced by Earth’s surface, responding to surface forcings within 30-60 min Comparison of PBL and Free Troposphere Characteristics PropertyPBLFT Turbulence Near continuous over Zi. Convective clouds; sporadic in thin layers extending horizontally. Friction Large drag & energy dissipation. Small viscous dissipation. Dispersion Rapid in vertical & horizontal. Small molecular diffusion; rapid horizontally by mean wind. Winds WS log profile in surface layer. Nearly geostrophic. Vertical Transport Mainly turbulence. Mean wind, cumulus-scale. Thickness 100 – 3000 m, f (time/space). 8 – 18 km, less variable. Diurnal oscillations over land. Slow time variations. EAS 4/8803

  21. Turbulence in PBL Assuming an air parcel rises or sinks adiabatically, i.e. no energy is supplied nor removed, it expands and cools as it reaches lower ambient pressure aloft, or compresses and warms as it reaches higher pressure below. If the ambient vertical temperature profile (lapse rate) is less steep, the air parcel will continue to rise or fall once in (vertical) motion. Superadiabatic T profile (unstable layer) EAS 4/8803

  22. Consequences for Dispersion/Dilution Weakly instable to neutral layer: Dispersion driven by advection (horizontal WS). Highly instable layer: Dispersion driven by thermal looping (vertical & horizontal). EAS 4/8803

  23. Effects of Terrain (Friction) EAS 4/8803

  24. Temperature Inversion Assuming an air parcel rises or sinks adiabatically, i.e. no energy is supplied nor removed, it expands and cools as it reaches lower ambient pressure aloft, or compresses and warms as it reaches higher pressure below. If the ambient vertical temperature profile (lapse rate) is steeper, the air parcel will return to its original position. Subadiabatic T profile (stable layer) EAS 4/8803

  25. Elevated Surface Inversion Types and Formation Subsidence inversion: Large scale sinking of cold (but warming) air meets rising cooling air (thermals) under regional high pressure conditions. Frontal inversion: Warm moist air from S glides over cold dry air from N. Radiational inversion: Radiative heat loss at night from the Earth’s ground into space according to sTg4. EAS 4/8803

  26. Typical PBL Evolution in Summer Stull, R. B., 1988: An Introduction to Boundary Layer Meteorology. Kluwer Academic, 666 pp. EAS 4/8803

  27. Afternoon After sunset Before sunrise After sunrise Before noon Noon Potential Temperature (Q) Profiles…is T an air parcel at P and T would have if it were at Ps(conserved for adiabatic motions, i.e., dq/dt = 0). EAS 4/8803

  28. PBL Winter vs Summer EAS 4/8803

  29. Seasonal Differences in Diurnal Cycles of PM2.5 Summer Winter Midday minimum due to BL mixing seems compensated by SOA in summer.PM2.5 sources near Columbus drive nighttime averages in winter 2001/02.Summer stagnation with high O3 also leads to high PM2.5 (e.g. 2000).Annual PM2.5 NAAQS (15 mg m-3) sensitive to:- SOA formed under regional stagnation in summer;- Primary PM2.5 from local sources at night in winter. EAS 4/8803

  30. PM2.5 Exceedances at Columbus in Oct-Nov 2001 EAS 4/8803

  31. PM2.5 at Columbus in Oct-Dec 2001 • Critical parameters driving [PM2.5]: • size of burn, distance and plume trajectory • atmospheric divergence (horizontal wind speed) • {vertical} boundary layer stability (T difference) • BL mixing depth at night (BLHnight) EAS 4/8803

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