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Continuous measurement of airborne particles and gases

Continuous measurement of airborne particles and gases. Jeff Collett and Taehyoung Lee. Atmospheric Science Department Colorado State University. Funding: USDA/AES and NPS. Outline. Why measure particles and gases at high time resolution? Examples of previous applications

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Continuous measurement of airborne particles and gases

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  1. Continuous measurement of airborne particles and gases Jeff Collett and Taehyoung Lee Atmospheric Science Department Colorado State University Funding: USDA/AES and NPS

  2. Outline • Why measure particles and gases at high time resolution? • Examples of previous applications • Measurement approach • Initial results • Summary and future research plans

  3. Emissions, transport and deposition of pollutants • Atmospheric particles can be emitted directly or produced by reactions in the atmosphere • Adverse impacts (health, visibility, ecosystem) occur on local to regional scales Aneja et al. (2006)

  4. Particle composition • Many particles in polluted atmospheres are combinations of ammonium with sulfate and/or nitrate Northern Front Range Air Quality Study – 1997 Winter

  5. Particle formation • Gaseous sulfur dioxide reacts to form particulate sulfuric acid/sulfate H2SO4(p) + 2NH3(g)  (NH4)2SO4(p) • Gaseous nitrogen oxides react to form gaseous nitric acid HNO3(g) + NH3(g) NH4NO3(p) • Particulate ammonium nitrate generally forms only when ammonia > sulfate Data from the IMPROVE program http://vista.cira.colostate.edu/improve/Default.htm

  6. Why measure particles + gases? • Particles are regulated • Regional haze rule • Health-based NAAQS • Gases are precursors to particle formation • Partitioning between gases and particles changes over time Contrasting afternoon visibilities at Great Sand Dunes NP

  7. Source characterization Emission rates change Upwind composition may change Wind direction changes source influence Ambient air quality Pollutant transport changes “Tracking” between species helps us understand composition Why measure at high time resolution?

  8. Nitrate and sulfate both important Acidic sulfate aerosol at times NH4NO3 and (NH4)2SO4 at times Example 1. changes in aerosol composition at an agricultural site in Illinois

  9. Example 2. Southern California mountain wilderness area • NH4NO3 particles dominate • Large daily variability tied to mountain-valley winds

  10. Example 3. Yosemite National Park • Note “tracking” of sodium and nitrate • Nitrate replaced chloride in sea salt HNO3(g) + NaCl(p)  NaNO3(p) + HCl(g)

  11. Fine (submicron) ammonium nitrate particles Favored at low T, high RH, high NH3 HNO3(g) + NH3(g) NH4NO3(p) Coarse (supermicron) reacted sea salt or soil dust particles More likely at high T and low NH3 HNO3(g) + NaCl(p)  NaNO3(p) + HCl(g) 2 HNO3(g) + CaCO3(p)  Ca(NO3)2(p) + CO2 + H2O Lesson: careful characterization of ammonia availability and chemical speciation of particle nitrate key to understanding impacts of agricultural ammonia on regional particle formation Particle nitrate

  12. summer summer summer summer Particle nitrate speciation

  13. New continuous measurement applications • Modify approach to permit gas + particle measurement at 10-15 min time resolution • Measure ammonia emissions from dairies • Make system mobile to permit upwind + downwind measurements • Examine impacts of emitted ammonia on airborne particle concentrations • Project runs: Fall 2005 – Summer 2008

  14. Conceptual picture +hv, VOC HNO3 + NH3  NH4NO3(p) NOx

  15. Measurement approach • Collect particles in liquid stream • Inject stream into ion chromatograph for chemical analysis • Switch between “gas+particle” and “particle only” sampling

  16. Field deploymentNovember, 2005 Modified Particle-Into-Liquid Sampler

  17. Initial Observations - Sulfate

  18. Initial Observations - Nitrate

  19. Initial Observations – Ammonia

  20. Initial Conclusions • Particle nitrate and sulfate agree well with filter measurements • Lots of ammonia • >> particle ammonium • Denuders to remove NH3(g) last only ~4-5 hours • Lose NH3(g) in instrument • Change sampler design to better capture NH3(g)

  21. Summary and future work • Nitrate and sulfate important components of airborne particles • NH3(g) availability affects particle formation • BUT, not all particle nitrate is NH4NO3 • New approach to semi-continuous particle + gas measurements can help resolve • Emissions • Changes in particle amount and composition due to emissions • Modifications are needed to measurement approach to • Improve NH3(g) collection efficiency (steam sampler) • Enhance capacity of denuder for NH3(g) removal in particle only measurement • Modified instruments will be redeployed • Look at particle and gas concentrations • At high time resolution • Over longer periods than feasible for manual filter-pack sampling • Evaluate how emissions vary between source types on a dairy

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