Update on PM2.5 – The Scope of the Problem and

Overview of Sources

Matthew M. Russell, PhD ENVIRON International Corporation

Los Angeles, CaliforniaApril 15, 2008

Definitions

TSP: Total Suspended Particulate (~<30 microns)

PM10: Coarse and Fine Particles: particles less than 10 microns in “diameter”

PM2.5 (Fine Particles): particles less than 2.5 microns in “diameter”

Ultrafine Particles (UFP): generally particles less than 0.1 microns in “diameter”

Nanoparticles: particles less than 50 nm (nanometers) in “diameter”– 1000 nm in a micron

Particulate Matter: What is it?

PM10

Combustion Particulate Matter

Gasoline exhaust particleDiesel exhaust particle

Source: D. Kittleson, SCAQMD Ultrafine Particle Conference

PM2.5 Sources

Secondary PM2.5 Aerosol Formation Ammonia is the source of the predominant base

compound in the atmosphere (ammonium – NH4+)

Acids are formed by reaction of combustion by-products– NO2 + OH → HNO3

– SO2 + 2OH → H2SO4

Under the right conditions, ammonia will join with gaseous acids (e.g. sulfuric and hydrochloric acids)– 2NH3(g) + H2SO4 → 2(NH4)SO4 (aerosol)

– NH3(g) + HNO3(g) ↔ NH4NO3(PM) (solid and aerosol)

Ammonium sulfate, then ammonium nitrate

Ammonia: The Step-Child of PM Precursors A necessary, but not sufficient precursor

– Wetter conditions with limited mixing conducive to ammonium aerosol production

– Sulfuric acid will preferentially react with any available ammonia first

– Ammonium nitrate will be formed ifadditional ammoniaavailable and conditions are conducive

Limiting reactant?

New control programs?

Source: After Pandis (2003)

PM National Ambient Air Quality Standards

PM2.5 Non-Attainment Areas

Primary sources of PM

Secondary sources of PM

EPA: PM2.5 Diesel (US)

Federal Programs Will Reduce PM2.5

But many areas will need additional controls

Example: South Coast Air Basin PM2.5

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5

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Nitric Acid Ammonia Nitrate-10 Ammonium-10

Anaheim Los Angeles Diamond Bar Fontana Rubidoux

20052001

Source: SCAQMD

What’s Next? Ultrafine Particles (UFP) Increasing scientific and technical study of

UFP– Health effects (number count and composition

more important than mass)– Sources and emissions– Ambient concentrations– Potential control programs

South Coast AQMD UFP Conference (April 2006)– Scientific and technical studies presented– Increasing regulatory interest at all levels

UFP and PM2.5

Potential control program interactions– Some, but not all, DPM filters may also be effective at reducing UFP– New UFP formation may be inversely proportional

to PM2.5 (!)

Research at USC suggests :

Source: Sioutas, C. SCAQMD Ultrafine Particle Conference

Conclusions

PM2.5 is comprised of many substances Combustion sources are the major sources of:

– primary PM2.5 (e.g., carbon soot, organic aerosols)– secondary precursors (NOx, SOx)– control programs for ozone can reduce PM2.5

Aggressive controls of combustion sources will be necessary to attain federal standards for worst areas

Ammonia as a precursor needs to be better understood, particularly for ammonia-limited areas

Ultrafine particles (UFP) and future related control programs may directly affect PM2.5 control programs