Update on PM 2.5 – The Scope of the Problem and Overview of Sources Matthew M. Russell, PhD ENVIRON International Corporation Los Angeles, California April 15, 2008

Definitions  TSP: Total Suspended Particulate (~<30 microns)  PM 10 : Coarse and Fine Particles: particles less than 10 microns in “diameter”  PM 2.5 (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?

PM 10

Combustion Particulate Matter Gasoline exhaust particle Diesel exhaust particle Source: D. Kittleson, SCAQMD Ultrafine Particle Conference

PM 2.5 Sources

Secondary PM 2.5 Aerosol Formation  Ammonia is the source of the predominant base compound in the atmosphere (ammonium – NH 4 +)  Acids are formed by reaction of combustion by-products –NO 2 + OH → HNO 3 –SO 2 + 2OH → H 2 SO 4  Under the right conditions, ammonia will join with gaseous acids (e.g. sulfuric and hydrochloric acids) –2NH 3 (g) + H 2 SO 4 → 2(NH 4 )SO 4 (aerosol) –NH 3 (g) + HNO 3 (g) ↔ NH 4 NO 3 (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 if additional ammonia available and conditions are conducive  Limiting reactant?  New control programs? Source: After Pandis (2003)

PM National Ambient Air Quality Standards

PM 2.5 Non-Attainment Areas

Primary sources of PM

Secondary sources of PM

EPA: PM 2.5 Diesel (US)

Federal Programs Will Reduce PM 2.5  But many areas will need additional controls

Example: South Coast Air Basin PM

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 PM 2.5  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 PM 2.5 (!)  Research at USC suggests : Source: Sioutas, C. SCAQMD Ultrafine Particle Conference

Conclusions  PM 2.5 is comprised of many substances  Combustion sources are the major sources of: –primary PM 2.5 (e.g., carbon soot, organic aerosols) –secondary precursors (NO x, SO x ) –control programs for ozone can reduce PM 2.5  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 PM 2.5 control programs