Environmental Engineering Reference
In-Depth Information
environmental variables with a level of skill which justifies the use of the system
for undertaking climate projection modelling for future decades. A detailed
analysis of changes in the important field related to ozone climatology such as
temperature, wind field and ventilation rate, is discussed in Cope et al. (2008).
Because model performance for ozone represents a test of the fully coupled
system, it is not possible to eliminate the possibility of error compensation (or
enhancement) due to biases in individual components of the system (i.e. emissions,
meteorology or chemistry). However our previous experience in modelling photo-
chemical smog production in Sydney suggests that the ability to simulate the
correct mesoscale flows is the most significant factor in determining whether
elevated concentrations of ozone will be correctly simulated by the chemical
transport model simulation for Sydney.
The majority of the modelled concentrations lie within 30% of the observed
concentrations from 16 monitoring stations. While overall the model has a tendency
to over-predict the lower percentile concentrations and to under-predict the upper
percentile concentrations, there is an excellent level of agreement between the
modelled and observed 50th, 75th, 80th and 100th percentile peak daily 1-h ozone
concentrations. With respect to the peak daily 4-h ozone concentrations, the detailed
performance is slightly worse than the daily peak 1-h ozone performance.
4. Projections
This section discusses the projected changes in peak ozone concentration for a
climate projection based on the A2 SRES emission scenario. In interpreting the
results in this section it must be noted that they correspond to downscaling based
on a single climate (A2) emissions scenario.
4.1. Projection with current emission levels
This section presents ozone change for decade 2 and decade 3 for a scenario in
which the emissions are fixed at 1996-2005 values. In the case of the second
decade, the majority of the changes in 1-h peak ozone from the first decade
concentrations are projected to vary in the range −5 to +10 ppb, with the majority
of the changes being positive. In the case of the third decade the majority of the
99th percentile 1-h concentrations are calculated to increase, with increases of up
to 15 ppb calculated. Recall that violation of the NEPM goals for ozone occurs
when more than one exceedence per year is recorded. The number and spatial
extent of the 4-h ozone exceedences are projected to increase in the second and
third decades.
