Premise PM5. Spatial gradients for primary particulate matter may be more pronounced
than those for secondary particulate matter or those for ozone. As previously noted,
secondary particulate matter and ozone result from an interaction of meteorology and chemistry
taking several hours to days. Because of the time scales and mixing required, sharp spatial
gradients in concentrations of these pollutants are unlikely. In contrast, primary particulate
matter is emitted in the form it appears at monitoring sites. It is likely that concentrations of
primary particulate matter are greatest near major source areas of primary particulate matter.
The preceding implies that it may be necessary to estimate concentrations of primary
particulate matter using models with finer spatial resolution than is necessary for secondary
particles. Further, there may be several sources or concentrations of sources of primary
particulate matter within an area designated as “nonattainment” for PM2.5. The guidance will
need to address how to evaluate model performance and how to estimate whether attainment of
the NAAQS is likely in such locations.
Premise PM6. Seasonal differences are likely in emissions of PM2.5 and its precursors, as
well as in meteorological conditions affecting source/receptor relationships. Emissions from
several potentially important sources of PM2.5 , such as residential wood burning, wildfires,
agricultural burning, prescribed burning and biogenic sources have distinctive seasonal patterns.
Further, meteorological factors which may affect PM2.5 or regional haze, such as relative
humidity, sunlight intensity, mixing heights, precipitation and temperature, have marked
seasonal differences in many parts of the United States. The annual NAAQS for PM2.5 and the
regional haze rule address a composite of conditions measured over many days. To understand
how such composites respond to changes in emissions, it will be necessary to model a variety of
days with varying emissions and meteorological conditions. This implies that States will need to
develop base emissions estimates for a full year (or multiple years) or a representative portion of
days may need to be modeled from each season.
n551 - n552 - n553 - n554 - n555 - n556 - n557 - n558 - n559 - n560 - n561 - n562 - n563 - n564 - n565 - n566 - n567 - n568 - n569 - n570 - n571 - n572 - n573 - n574 - n575 - n576 - n577 - n578 - n579 - n580 - n581 - n582 - n583 - n584 - n585 - n586 - n587 - n588 - n589 - n590 - n591 - n592 - n593 - n594 - n595 - n596 - n597 - n598 - n599 - n600
castellano: DISPER CUSTIC DESCAR RADIA italiano:
deutsch: DIS CUS DES RAD
castellano: DIS CUS DES RAD english: DIS CUS DES RAD
português: DIS CUS DES RAD italiano: DIS CUS DES RAD
français: DIS CUS DES RAD