Environmental Engineering Reference
In-Depth Information
variability on VOC/NO
x
sensitivity (Bärtsch-Ritter et al., 2004) and the variability
in emissions. The ozone changes on weekly and long-term scales are caused pri-
marily by anthropogenic emission changes, while changes at the hourly, diurnal,
synoptic and seasonal scales are mainly influenced by meteorology.
Investigative
methods such as “zeroing out” approaches of specific sources of emissions can serve
as a preliminary guide for the development of control strategies. This methodology
is applied in this study to inter-compare impact of relative emission distribution
patterns in the four ozone near non-attainment areas (Austin, San Antonio, Corpus
Christi and Victoria), which have had several high ozone days in recent times
despite being in attainment of the federal air quality standards. The study will also
evaluate the fluctuations in the impact on air quality for two separate high ozone
episodes. Ozone exceedances are extremely important from the standpoint of
human health. Impact assessment of emissions was evaluated on both the number
of exceedances and their spatial extent based on EPA's new standards for ozone.
The results from these preliminary investigations depict ozone benefits arising from
emissions controls exhibit substantial episode-episode fluctuations thus reiterating
the need to consider multiple ozone episodes in order to reduce uncertainties while
developing effective emission control strategies.
2. Model Setup
The photochemical model (CAMx) version 3.1 and 4.1 was applied in a nested
mode (36, 12 and 4) km with the innermost grid encompassing all the near non-
attainment areas (NNA) of south and central Texas for 1999 and 2002 respec-
tively. Hourly meteorological data from MM5 simulations were used for both the
episodes. Emissions processor EPS version 2 and 3 was employed to generate
hourly CAMx ready gridded emissions input files for the two ozone episodes
September 13-20, 1999 and September 8-16, 2002, respectively, over south and
central Texas. Details of the September 1999 model set up are provided by Emery
et al. (2003) and that of September 2002 are provided by Farooqui M.Z. (2008).
3. Methodology
The index of improvement of modeled O
3
concentrations was computed for
n25v50 (25% NO
x
emission reduction and 50% VOC emission reduction) and
n50v25 (50% NO
x
emission reduction and 25% VOC emission reduction) emis-
sion control runs relative to the base case (n00v00) run. “Zero-out emission runs”
from area, on-road mobile, non-road mobile, point, anthropogenic, and biogenic
emission sources were conducted. The impact of emission sensitivity runs on
ozone exceedances was assessed by computing the reduction in the number of
exceedances and in spatial extent of exceedances within the study domain.
