Environmental Engineering Reference
In-Depth Information
Answer:
Data from the National Park Service passive ozone monitoring program
suggest an increasing trend in seasonal mean ozone concentrations at some
parks in California and Oregon that are not immediately downwind of local
emission source regions, specifically, Crater Lake National Park, Lava Beds
National Monument, and Point Reyes National Seashore, and so are not neces-
sarily inconsistent with other trend data. The magnitudes of the observed changes
at these west-coast parks are not large enough to explain the trends in the annual
fourth-highest peak daily 8-h ozone at compliance-monitoring sites in central
California, or the spatial variations of the central California peak ozone trends.
Question:
First, do NMOC include biogenics and has the relative fraction of
“controllable” VOC changed? Second, NO
x
decrease causes an OH radical
increase, so ambient VOC should decrease faster than emissions; is that an
explanation for the more rapid decrease of ambient NMOC concentrations than
of VOC emissions?
Answer:
The NMOC data are from the PAMS program's canister samples and
continuous measurements, both of which represent total nonmethane organic
compounds. Total NMOC includes biogenic compounds that are captured by
the sampling methods. However, isoprene is the only individually-measured
biogenic compound. Our data do not answer the question of the effect of NO
x
on ambient NMOC concentrations and trends. Another possible explanation for
the discrepancy between ambient and emissions NMOC trends is that the
ambient trends at the seven NMOC monitoring sites may not be representative
of the entire domain. The ambient trends were more similar to county-level and
multi-county emission trends than to either local (within 28 × 28 km areas
around monitors) or domain-wide emission trends.
