Model assessment and verification - Air Pollution Modeling and Its Application - page 355

4.15 Assessment of CALPUFF for Modeling
Winter-Time PM 10 in Christchurch, New Zealand
Vicky Lucas
Environment Canterbury, 58 Kilmore Street, P.O. Box 345, Christchurch 8140, New Zealand
Abstract Christchurch, in New Zealand's South Island, has PM 10 concentrations
in winter that exceed the WHO 24-hour guidelines. CALPUFF has been used to
model the distribution of PM 10 concentrations across the city of Christchurch
during winter 2005 and 2006. CALMET was shown to effectively develop the
terrain induced surface flows that affect Christchurch on light-wind evenings. The
modeling of wintertime PM 10 in the city was verified against measured data at two
sites. The model captured diurnal variability well but daily values were generally
too high, although the long term averages were shown to be within 10% of the
measured values. The model was able to predict high pollution days with
reasonable skill, with a rank correlation of 0.63 to 0.80.
Keywords CALPUFF, CALMET, particulate matter
1. Background
Christchurch is the largest city in New Zealand's South Island, home to 350,000
people. The city has generally good air quality with respect to gaseous pollutants
such as ozone and sulfur dioxide, but in wintertime the city experiences PM 10
(particulate matter of less than 10 μm) concentrations that exceed the 2005 World
Health Organization 24-h guidelines of 50 μg/m 3 . Between May and August 2006
the city exceeded the guideline value on 27 days. City-wide emission inventories
indicate that the main emission of winter PM 10 is from burning wood to heat
homes. The 2006 inventory indicated that on a cold winters' day 76% of the mass
of PM 10 emitted was by domestic wood burning, 11% by motor vehicles and the
remaining 13% was emitted by industrial activities [4].
Environment Canterbury is the local government body responsible for air quality
in Christchurch. The development of modeling that captures patterns of ambient
PM 10 is helpful for investigating ways of improving air quality and thereby
informing policy decisions. The first step is to develop and verify the model.