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 NH3(g) source

Instrumentation

• Filter-based sampling– PM10 (Da < 10 m)– Fine particulate matter (Da < 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 TrajectoryAugust 27-28, 1997

8/2714:00-18:00

8/27-2818:00-01:0001:00-06:0006:00-10:00

Fine PM Mass Balance Central Los Angeles Aug 27-28, 1997

• Strong diurnal cycle, maximum during daylight• Carbon dominates fine PM mass

24 06 12 18 24 06 12 18 240

20

40

60

Con

cent

ratio

n (

g m

-3)

27-Aug 28-Aug

Central Los AngelesUnidentified Cl- Na+ SO

4=

NH4+

NO3-

Metals and Metal OxidesOrganic Compounds Elemental Carbon

Impactor Mass BalancesCentral Los Angeles Aug 28, 1997

0.02 0.05 0.1 0.2 0.5 10

20

40

60

M

/

log

Da (

g m

-3)

Aerodynamic Diameter, Da (m)

Impactor Mass BalanceCentral Los Angeles28-Aug-1997, 14:00 - 18:00 PDT

0.02 0.05 0.1 0.2 0.5 10

20

40

60

M

/

log

Da (

g m

-3)

Aerodynamic Diameter, Da (m)

Impactor Mass BalanceCentral Los Angeles28-Aug-1997, 06:00 - 10:00 PDT

06:00-10:00 PDT 14:00-18:00 PDT

Unidentified Cl- Na+ SO

4=

NH4+

NO3-

Metals and Metal OxidesOrganic Compounds Elemental Carbon

• Elemental carbon peaks during morning traffic• Decrease in fine carbon particles later in day• Shift in carbon peak• NO3

- mainly present >1.0m, as NaNO3

Fine PM Mass Balance Along Trajectory

• Local quarry source in Azusa• Increase in EC, org. matter with rush hour• Little change in other species

24 06 12 18 24 06 12 18 240

20

40

60

Con

cent

ratio

n (

g m

-3)

21-Aug 22-Aug

LosAngeles

AzusaUnidentified Cl- Na+ SO

4=

NH4+

NO3-

Metals and Metal OxidesOrganic Compounds Elemental Carbon

Nitrogen Balance Along Trajectory

• Little ammonium nitrate formation

• NO, NO2 increase with morning rush hour

24 06 12 18 24 06 12 18 240

50

100

Con

cent

ratio

n (

g N

m-3

)

21-Aug 22-Aug

LosAngeles

Azusa NH4+

NO3-

NH3

HNO3

NO2

NO

Single-Particle Evolution Along Trajectory1.8 – 3.5 m

• Azusa before 06:00 very similar to Central LA• Increase in carbon-containing particles,

“complex” particles with rush hour

Central LA 8/2114:00-18:00 PDT

Azusa 8/2206:00-10:00 PDT

1.80 - 3.50 m 1.80 - 3.50 m

Single-Particle Evolution Along Trajectory1.0 – 1.8 m

• Azusa dust presence from local quarry source• Increased ammonium presence

Central LA 8/2114:00-18:00 PDT

Azusa 8/2206:00-10:00 PDT

1.00 - 1.80 m 1.00 - 1.80 m

Single-Particle Evolution Along Trajectory0.56 – 1.8 m

• Higher presence of “carbon-only” particles in Central LA during evening rush hour

• More “complex” carbon particles in Azusa

Central LA 8/2114:00-18:00 PDT

Azusa 8/2206:00-10:00 PDT

0.56 - 1.00 m 1.80 - 3.50 m

Nitrate-Oriented Trajectory StudyDiamond Bar - Mira Loma

October 31-November 1. 1997

10/3106:00-10:00

10/31-11/118:00-01:00

Fine PM Mass Balance Diamond Bar Oct 31-Nov 1, 1997

24 06 12 18 24 06 12 18 240

50

100

150

200

Con

cent

ratio

n ( g

m-3

)

31-Oct 01-Nov

Diamond BarFine Particle Mass Balance

• EC peak weekday rush hour, not weekend• Air sampled in 1400-1800 minimum spent 1-2 fewer days over land

Unidentified Cl- Na+ SO

4=

NH4+

NO3-

Metals and Metal OxidesOrganic Compounds Elemental Carbon

0.02 0.05 0.1 0.2 0.5 10

50

100

150

200

M

/

log

Da (

g m

-3)

Aerodynamic Diameter, Da (m)

Impactor Mass BalanceDiamond Bar31-Oct-1997, 14:38 - 18:00 PST

0.02 0.05 0.1 0.2 0.5 10

50

100

150

200

M

/

log

Da (

g m

-3)

Aerodynamic Diameter, Da (m)

Impactor Mass BalanceDiamond Bar31-Oct-1997, 10:00 - 14:00 PST

Impactor Mass BalancesDiamond Bar Oct 31, 1997

10:00-14:00 PST 14:00-18:00 PDT

Unidentified Cl- Na+ SO

4=

NH4+

NO3-

Metals and Metal OxidesOrganic Compounds Elemental Carbon

• Aerosol NH4NO3 in particles > 0.3 m • Morning: NH4NO3 production, air stagnated northeast• Afternoon: relatively clean, air stagnated west

Nitrogen Balance Along Trajectory

• Ammonium nitrate HNO3-limited in Diamond Bar

• Gas-phase ammonia concentration increases 5

24 06 12 18 24 06 12 18 240

50

100

150

200

Con

cent

ratio

n (

g N

m-3

)

31-Oct 01-Nov

DiamondBar

MiraLoma

NH4+

NO3-

NH3

HNO3

NO2

NO

Fine PM Mass Balance Along Trajectory

• Note Federal Ambient Air Quality Standard: 65 g m-3

24 06 12 18 24 06 12 18 240

50

100

150

Con

cent

ratio

n (

g m

-3)

31-Oct 01-Nov

DiamondBar

MiraLoma

Unidentified Cl- Na+ SO

4=

NH4+

NO3-

Metals and Metal OxidesOrganic Compounds Elemental Carbon

11/101:00-06:0010/31

01:00-06:00

Nitrate-Oriented Trajectory StudyMira Loma - Riverside

October 31-November 1, 1997

Nitrogen Balance Along Trajectory

• Air parcel over land ~3 days before Mira Loma

• NH3 concentration decrease with distance from dairy “point source”

24 06 12 18 24 06 12 18 240

50

100

150

200

Con

cent

ratio

n (

g N

m-3

)

31-Oct 01-Nov

MiraLoma

Riverside NH4+

NO3-

NH3

HNO3

NO2

NO

Fine PM Mass Balance Along Trajectory

• Ammonium and nitrate concentrations similar

24 06 12 18 24 06 12 18 240

50

100

150

Con

cent

ratio

n (

g m

-3)

31-Oct 01-Nov

MiraLoma

RiversideUnidentified Cl- Na+ SO

4=

NH4+

NO3-

Metals and Metal OxidesOrganic Compounds Elemental Carbon

Change in Particle Population with Wind Shift1.8 – 3.5 m

• Number of fine particles decreases by 86%• After shift, population dominated by dust and

“uncomplex” particles

Riverside 11/101:00-06:00 PSTWind from West

Riverside 11/110:00-14:00 PSTWind from North

1.80 - 3.50 m 1.80 - 3.50 m

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 NO3

- and NH4+

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)