Evolution of Atmospheric Aerosols Along Trajectories Crossing the Los Angeles Basin February 15, 2001 Lara H. Gertler (UC-Riverside) Jonathan O. Allen (Arizona State University) Sylvia H. Pastor (UC-Riverside) Glen R. Cass (Georgia Inst. of Technology) Kimberly A. Prather (UC-Riverside)

Problems Models used to predict particle population to aid design of effective control programs –Experimental data difficult to obtain: want size distribution of chemical composition and at single particle level within same air parcel over time to evaluate trajectory model for externally mixed aerosol

Research Objectives Acquire field experimental data documenting particle chemical evolution over time within individual air parcels –Data specifically for use in future air quality model evaluation studies

Approach to gathering trajectory-based size and chemical composition data: Choose air monitoring sites along a typical air parcel trajectory Pair conventional samplers with aerosol time- of-flight mass spectrometry (ATOFMS) instruments collecting single particle data After sampling, identify air parcel trajectories that successively passed over multiple sites Examine particle population changes during transport along these trajectories

Vehicle-Oriented Trajectory Study August, 1997 Focused on air parcels exposed to motor vehicle primary emissions

Nitrate-Oriented Trajectory Study September-November, 1997 Examined particulate ammonium nitrate formation with exposure to large NH 3 (g) source

Instrumentation Filter-based sampling –PM 10 (D a < 10  m) –Fine particulate matter (D a < 1.8  m) Electrical aerosol analyzer (EAA) Laser optical particle counter (OPC) Pair of micro-orifice impactors (MOI) Aerosol time-of-flight mass spectrometry (ATOFMS) instrument

Vehicle-Oriented Trajectory August 27-28, /27 14:00-18:00 8/ :00-01:00 01:00-06:00 06:00-10:00

Fine PM Mass Balance Central Los Angeles Aug 27-28, 1997 Strong diurnal cycle, maximum during daylight Carbon dominates fine PM mass Concentration (  g m -3 ) 27-Aug28-Aug Central Los Angeles

Impactor Mass Balances Central Los Angeles Aug 28, :00-10:00 PDT14:00-18:00 PDT Elemental carbon peaks during morning traffic Decrease in fine carbon particles later in day Shift in carbon peak NO 3 - mainly present >1.0  m, as NaNO 3

Fine PM Mass Balance Along Trajectory Local quarry source in Azusa Increase in EC, org. matter with rush hour Little change in other species Concentration (  g m -3 ) 21-Aug22-Aug Los Angeles Azusa

Nitrogen Balance Along Trajectory Little ammonium nitrate formation NO, NO 2 increase with morning rush hour

Single-Particle Evolution Along Trajectory 1.8 – 3.5  m Azusa before 06:00 very similar to Central LA Increase in carbon-containing particles, “complex” particles with rush hour Central LA 8/21 14:00-18:00 PDT Azusa 8/22 06:00-10:00 PDT

Single-Particle Evolution Along Trajectory 1.0 – 1.8  m Azusa dust presence from local quarry source Increased ammonium presence Central LA 8/21 14:00-18:00 PDT Azusa 8/22 06:00-10:00 PDT

Single-Particle Evolution Along Trajectory 0.56 – 1.8  m Higher presence of “carbon-only” particles in Central LA during evening rush hour More “complex” carbon particles in Azusa Central LA 8/21 14:00-18:00 PDT Azusa 8/22 06:00-10:00 PDT

Nitrate-Oriented Trajectory Study Diamond Bar - Mira Loma October 31-November /31 06:00-10:00 10/31-11/1 18:00-01:00

Fine PM Mass Balance Diamond Bar Oct 31-Nov 1, 1997 EC peak weekday rush hour, not weekend Air sampled in minimum spent 1-2 fewer days over land

Impactor Mass Balances Diamond Bar Oct 31, :00-14:00 PST 14:00-18:00 PDT Aerosol NH 4 NO 3 in particles > 0.3  m Morning: NH 4 NO 3 production, air stagnated northeast Afternoon: relatively clean, air stagnated west

Nitrogen Balance Along Trajectory Ammonium nitrate HNO 3 -limited in Diamond Bar Gas-phase ammonia concentration increases  Concentration (  g N m -3 ) 31-Oct01-Nov Diamond Bar Mira Loma

Fine PM Mass Balance Along Trajectory Note Federal Ambient Air Quality Standard: 65  g m Concentration (  g m -3 ) 31-Oct01-Nov Diamond Bar Mira Loma

11/1 01:00-06:00 10/31 01:00-06:00 Nitrate-Oriented Trajectory Study Mira Loma - Riverside October 31-November 1, 1997

Nitrogen Balance Along Trajectory Air parcel over land ~3 days before Mira Loma NH 3 concentration decrease with distance from dairy “point source” Concentration (  g N m -3 ) 31-Oct01-Nov Mira Loma Riverside

Fine PM Mass Balance Along Trajectory Ammonium and nitrate concentrations similar Concentration (  g m -3 ) 31-Oct01-Nov Mira Loma Riverside

Change in Particle Population with Wind Shift 1.8 – 3.5  m Number of fine particles decreases by 86% After shift, population dominated by dust and “uncomplex” particles Riverside 11/1 01:00-06:00 PST Wind from West Riverside 11/1 10:00-14:00 PST Wind from North

Further Work Trajectory-based data on particle evolution designed for use in air quality model evaluation –Impactor data along Sept 24-25,1996 Long Beach - Fullerton - Riverside trajectory already utilized this way –Next use impactor data from Vehicle- and Nitrate-Oriented Trajectory studies

Simultaneous operation of impactors and ATOFMS instruments allows calculation of ATOFMS counting efficiencies and ion sensitivities –Counting efficiencies and NO 3 - and NH 4 + ion sensitivities determined for 1996 data –Further counting efficiency and ion sensitivity investigation using 1997 data –Investigation of “matrix effects”

Thanks for funding from: California Air Resources Board Coordinating Research Council, Inc. U.S. DOE Office of Heavy Vehicle Technologies Thanks for assistance and contributions from: Dr. Kimberly Prather’s UC-Riverside research group Dr. Mike Kleeman (UC-Davis) Lynn Salmon (Caltech) Dr. Michael Ames (MIT) Nehzat Motallebi (CARB) Joe Cassmassi (SCAQMD) Rudy Eden (SCAQMD) Kevin Durkee (SCAQMD) Leon Dolislager (CARB) Clinton Taylor (CARB)