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. Data from the IMPROVE program
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

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. Why measure at high time resolution?
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

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

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. Particle nitrate 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

12. Particle nitrate speciation
summer

13. New continuous measurement applications
Modify approach to permit gas + particle measurement at 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
August average MOUDI distributions

16. Field deployment November, 2005
August average MOUDI distributions
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