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 Measurement approach Initial results Summary and future research plans
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)
Particle composition Many particles in polluted atmospheres are combinations of ammonium with sulfate and/or nitrate Northern Front Range Air Quality Study 1997 Winter
Particle formation Gaseous sulfur dioxide reacts to form particulate sulfuric acid/sulfate H 2 SO 4 (p) + 2NH 3 (g) (NH 4 ) 2 SO 4 (p) Gaseous nitrogen oxides react to form gaseous nitric acid HNO 3 (g) + NH 3 (g) NH 4 NO 3 (p) Particulate ammonium nitrate generally forms only when ammonia > sulfate Data from the IMPROVE program http://vista.cira.colostate.edu/improve/default.htm
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
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
Example 1. changes in aerosol composition at an agricultural site in Illinois 36 31 NH4+_ug/m3 NO3-_ug/m3 SO4=_ug/m3 26 21 Nitrate and sulfate both important Acidic sulfate aerosol at times 16 NH 4 NO 3 and (NH 4 ) 2 SO 4 at times 11 6 1 Concentration, ug/m3 2/2/2003 2/3/2003 2/4/2003 2/5/2003 2/6/2003 2/7/2003 2/8/2003 2/9/2003 2/10/2003 2/11/2003 2/12/2003 2/13/2003 2/14/2003 2/15/2003 2/16/2003 2/17/2003 2/18/2003 2/19/2003 2/20/2003 2/21/2003 2/22/2003 2/23/2003 Date
Example 2. Southern California mountain wilderness area 700 600 NH4+, neq/m3 NO 3-, neq/m 3 SO4=, neq/m3 500 400 300 200 NH 4 NO 3 particles dominate Large daily variability tied to mountain-valley winds Concentration, neq/m3 100 0 4/4 4/5 4/6 4/7 4/8 4/9 4/10 4/11 4/12 4/13 4/14 4/15 4/16 4/17 4/18 4/19 4/20 4/21 4/22 4/23 4/24 4/25 4/26 4/27
Example 3. Yosemite National Park Note tracking of sodium and nitrate Nitrate replaced chloride in sea salt HNO 3 (g) + NaCl(p) NaNO 3 (p) + HCl(g) 30 25 Cl- NO3- Na+ 20 neq/m3 15 10 5 0 8/12 8/13 8/14 8/15 8/16 8/17 8/18 8/19 8/20 8/21 8/22 8/23 8/24 8/25 8/26 8/27
Particle nitrate Fine (submicron) ammonium nitrate particles Favored at low T, high RH, high NH 3 HNO 3 (g) + NH 3 (g) NH 4 NO 3 (p) Coarse (supermicron) reacted sea salt or soil dust particles More likely at high T and low NH 3 HNO 3 (g) + NaCl(p) NaNO 3 (p) + HCl(g) 2 HNO 3 (g) + CaCO 3 (p) Ca(NO 3 ) 2 (p) + CO 2 + H 2 O Lesson: careful characterization of ammonia availability and chemical speciation of particle nitrate key to understanding impacts of agricultural ammonia on regional particle formation
NaNO3 54% Ca(NO3)2 41% NH4NO3 5% NaNO3 40% Ca(NO3)2 35% NH4NO3 25% NH4NO3 49% Ca(NO3)2 7% NaNO3 44% NH4NO3 55% Ca(NO3)2 6% NaNO3 39% NaNO3 73% Ca(NO3)2 26% NH4NO3 1% NH4NO3 84% Ca(NO3)2 7% NaNO3 9% NaNO3 49% Ca(NO3)2 15% NH4NO3 36% NH4NO3 80% Ca(NO3)2 16% NaNO3 4% summer summer summer summer Particle nitrate speciation
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
Conceptual picture +hv, VOC HNO 3 + NH 3 NH 4 NO 3 (p) NO x
Measurement approach Collect particles in liquid stream Inject stream into ion chromatograph for chemical analysis Switch between gas+particle and particle only sampling
Field deployment November, 2005 Modified Particle-Into-Liquid Sampler
Initial Observations - Sulfate 2.0 1.5 1.0 0.5 0.0 µg/m3 11/17/2005 12:00 11/17/2005 18:00 11/18/2005 0:00 11/18/2005 6:00 11/18/2005 12:00 11/18/2005 18:00 11/19/2005 0:00 11/19/2005 6:00 11/19/2005 12:00 11/19/2005 18:00 11/20/2005 0:00 11/20/2005 6:00 11/20/2005 12:00 11/20/2005 18:00 11/21/2005 0:00 11/21/2005 6:00 11/21/2005 12:00 Total = particle + SO2 Particle sulfate
Initial Observations - Nitrate 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 11/17/2005 12:00 11/17/2005 18:00 11/18/2005 0:00 11/18/2005 6:00 11/18/2005 12:00 11/18/2005 18:00 11/19/2005 0:00 11/19/2005 6:00 11/19/2005 12:00 11/19/2005 18:00 11/20/2005 0:00 11/20/2005 6:00 11/20/2005 12:00 11/20/2005 18:00 11/21/2005 0:00 11/21/2005 6:00 µg/m3 11/21/2005 12:00 Total = particle + HNO3 Particle nitrate
100 90 80 70 60 50 40 30 20 10 0 Initial Observations Ammonia µg/m3 11/17/2005 12:00 11/17/2005 18:00 11/18/2005 0:00 11/18/2005 6:00 11/18/2005 12:00 11/18/2005 18:00 11/19/2005 0:00 11/19/2005 6:00 11/19/2005 12:00 11/19/2005 18:00 11/20/2005 0:00 11/20/2005 6:00 11/20/2005 12:00 11/20/2005 18:00 11/21/2005 0:00 11/21/2005 6:00 11/21/2005 12:00 Total = particle +NH3 Particle ammonium
Initial Conclusions Particle nitrate and sulfate agree well with filter measurements Lots of ammonia >> particle ammonium Denuders to remove NH 3 (g) last only ~4-5 hours Lose NH 3 (g) in instrument Change sampler design to better capture NH 3 (g) URG (ug/m3) 2 1.5 1 0.5 P-NO3 P-SO4= T-NO3 T-SO4= 1:1 0 0 0.5 1 1.5 2 PILS (ug/m3)
Summary and future work Nitrate and sulfate important components of airborne particles NH 3 (g) availability affects particle formation BUT, not all particle nitrate is NH 4 NO 3 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