Seasonal Pattern: Background and Rationale

1
Seasonal Pattern Background and Rationale

• The seasonal cycle results from changes in PM
  background levels, emissions, atmospheric
  dilution, as well as chemical/removal processes.
• Examining the seasonal cycles of PM2.5 mass and
  its elemental constituents can provide insights
  in these causal factors.
• The season with the highest concentration is a
  good candidate for PM2.5 control actions.

2
Seasonal Maps of PM2.5

• The PM2.5 peaks during the summer, Q3, in the
  Eastern US.
• In populated regions of the Western US and the
  San Joaquin Valley the PM2.5 peaks in the
  winter.

3
Seasonal Charts PM2.5

• At Washington DC and Philadelphia the PM2.5
  increases 60 from winter to summer. In the
  Rural Appalachians the summer PM2.5 is a factor
  of three higher than during the winter.
• The PM2.5 at Urban Southwestern sites are winter
  peaked with 50 more PM2.5 during December than
  the summer. The rural sites are spring-summer
  peaked with 50 more PM2.5 during June than
  January.

4
Seasonal Urban-Rural Difference

• The excess PM2.5 at Washington DC ranges from gt10
  ug/m3 in the winter to 1-2 ug/m3 in the summer.
• The Phoenix excess PM2.5 ranges from 11 - 16
  ug/m3 in the winter to 3 ug/m3 in the summer.