Environmental Engineering Reference
In-Depth Information
Stockton, and Modesto actually had higher PM2.5 concentrations. This indicates
that surface PM conditions can have a different temporal trend than AOD.
Differences of model surface PM2.5 from CMAQ/CB05 and CMAQ/SAPRC99
were seen with some PM2.5 species. CMAQ/CB05 ammonia and nitrate were
obviously larger than CMAQ/SAPRC99 values, but CMAQ/SAPRC99 SOA and
sulfate were larger than CMAQ/CB05 values. The total surface CMAQ/CB05
PM2.5 was larger than CMAQ/SAPRC PM2.5, although the difference was not
significant. Between modeled surface PM2.5 and modeled PM2.5 with no water
contents (dry PM2.5), the model dry PM2.5 was much closer to the observations
throughout the sites in the valley. The CMAQ simulated PM2.5 water component
seems unrealistically high. PM2.5 observations were from Beta Attenuation
Monitors (BAM). Typical operation protocols for BAM specify heating of the
inlet line to a temperature about 30°C in order to reduce relative humidity to
below 60% (Chung et al., 2001). However, in winter time, relative humidity in the
valley can be 100% for a sustaining period of time. The BAM PM2.5 observations
do not have all the water contents in PM2.5. Based on this study, the CMAQ
modeled dry PM2.5 seems to be what should be used in a model evaluation
against BAM hourly observations. The model dry PM2.5 concentrations were
close to the observed PM2.5 except on the 17th and 18th. Analyses showed that
biases of the modeled meteorological conditions contributed significantly to the
discrepancies on these 2 days.
Acknowledgments
The authors would like to thank Jay Al-Saadi, James Szykman at the NASA
for providing the HSRL data. The airplane field study in the Central Valley was sponsored by the
US EPA under the Advance Monitoring Initiative.
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