Environmental Engineering Reference
In-Depth Information
increase in frequency of stagnation episodes and robust increase of temperature
which affects ozone either through PAN chemistry or through increased biogenic
emissions (Jacob and Winner, 2009). Ozone increases are found to be mostly in
the range of 1-10 ppb depending on the future decades and the region examined,
the climate scenario which is adopted and the model system used. It is not easy to
separate the effects of different meteorological parameters on air quality in the real
atmosphere because the interaction between them is complex and there are several
feedback mechanisms. A holistic approach is to study the impact of climate change
on air quality which is a far more complicated task involving climate change,
feedbacks with climate-dependent biogenic emissions and changes in future anthro-
pogenic emission trends.
This paper presents a modeling system of a regional climate model off-line
coupled to a regional chemistry transport model used for the assessment of present
and future air quality. In the current study it is assumed that there are no changes
in future emissions and the background species. Constant anthropogenic emissions
and chemical boundary conditions are used for the present and future decades.
Differences in tropospheric surface ozone can thus attributed only to climate change.
2. Modeling System
The modeling system applied to simulate climate/air quality over Europe is RegCM/
CAMx. RegCM was originally developed at the National Centre for Atmospheric
Research (NCAR) and has been mostly applied to studies of regional climate and
seasonal predictability. The air quality model simulations were performed with the
Comprehensive air quality model with extensions (CAMx) version 4.40 (www.
camx.com). CAMx is off-line coupled to RegCM with a fortran-based code we
developed, reading the basic meteorological parameters from RegCM (wind,
temperature, water, cloud/rain, pressure and vertical diffusivity) and exporting
them to CAMx-ready format. The spatial resolution of CAMx was set to 50 × 50
km. The domain's vertical profile contains 12 layers of varying thickness. Layer 1
is 36 m deep and the uppermost layer is 1.2 km thick and extends to about 6.5 km.
Top and lateral boundary conditions were kept constant corresponding to a clean
atmosphere. The chemistry mechanism invoked is Carbon Bond version 4 (CB4).
This mechanism includes 117 reactions - 11 of which are photolytic - and up to
67 species (37 gasses, 12 radicals and up to 18 particulates). Calculation of
emissions is presented in detail in Krueger et al., 2008. We shortly mention that
biogenic emissions are calculated on-line using temperature and radiation data
from RegCM and anthropogenic emissions are taken from the EMEP database for
the reference year 2000.
The runs presented in this work cover the time slice 1991-2000 and 2040-
2050. RegCM was forced by the ECHAM5 global circulation model for the
simulations covering the two time-slices. ECHAM5 run under the IPCC A1B
scenario to provide forcing for the future decade.
