Environmental Engineering Reference
In-Depth Information
2.32 Regional Background Fine Particulate Matter
Sergey L. Napelenok
1
, Jeffrey Arnold
1
, Kristen M. Foley
1
,
and Daven K. Henze
2
1
United States Environmental Protection Agency
2
University of Colorado, Boulder, CO, USA
Abstract
A modeling system composed of the global model GEOS-Chem
providing hourly lateral boundary conditions to the regional model CMAQ was
used to calculate the policy relevant background level of fine particulate matter.
Simulations were performed for the full year of 2004 over the domain covering
the continental United States. The influence on particulate matter from boundary
conditions was quantified using the decoupled direct method in three dimensions.
Similar to base CMAQ particulate concentrations themselves, background levels
and the influence of the boundaries were found to be highly variable spatially and
temporally in the domain. Particulate matter background levels were found to
range between 0.62 and 1.72 μg/m
3
averaged annually with higher values in the
southeastern part of the domain subject to high concentrations of organics from
fire emissions and the formation of secondary organic aerosols. The influence
from the boundary ranged 0.39-0.53 μg/m
3
averaged annually.
1. Introduction
Due to recent gains in scientific understanding of the processes governing
formation and transport of air pollutants, as well as technological advances in
pollutant control, ambient concentrations of ozone and particulate matter (PM)
have decreased significantly over the past decade over the European and North
American continents. However, further improvements in air quality are both
feasible and necessary in order to reduce unhealthy levels of exposure and to
improve visibility. As air quality standards tighten to target further reductions
in PM, ozone, and other species, the concept of the background or natural
concentration of pollutants becomes more important. This quantity is useful to the
regulatory communities where it is also known as the policy relevant background
(PRB). Here, the PRB of fine particulate matter (PM
2.5
) is investigated by region
in the United States for the full year of 2004. For the purposes of this analysis,
PRB is defined as the pollutant concentrations resulting from non-anthropogenic
emissions sources within North America and all emissions sources elsewhere.
