Page 38 - Swale AQMA Feasibility Study April 2020_

AQMA Feasibility Assessment
A2 – Keycol Hill and Key Street, Swale

Model Verification

Model verification studies are undertaken in order to check the performance of
dispersion models and, where modelled concentrations are significantly different
to monitored concentrations, a factor can be established by which the modelled
results can be adjusted in order to improve their reliability. The model
verification process is detailed in LAQM.TG(16). It should be noted that within
both the verification and assessment, the A249 Underpass was modelled as an
area source at ground level, following guidance provided by CERC. As of current,
ADMS cannot model emissions below ground-level, so this was deemed an
appropriate alternative method.

According to LAQM.TG(16), no adjustment factor is necessary where the results
of the model all lie within 25% of the monitored concentrations.

Model verification can only be undertaken where there is sufficient roadside
monitoring data in the vicinity of the subject scheme being assessed.
LAQM.TG(16) recommends that a combination of automatic and diffusion tube
monitoring data is used; although this may be limited by data availability. 10
monitoring locations along the A2 with appropriate traffic data were selected for
this study.

Table B.1 compares 2018 monitored and modelled total (road contribution +
background) NO2 concentrations at the monitoring locations.

Table B.1: Monitored and Modelled Total NO2 at Roadside Monitoring Sites
(2018)

-3
Concentrations (μg.m )
Monitor Type
ID
Monitored Modelled % Difference
ZW6 A 29.1 20.8 -28.6%

SW20 DT 26.1 20.3 -22.4%

SW37 DT 33.7 25.4 -24.7%

SW38 DT 31.1 20.7 -33.6%

SW45 DT 39.7 28.9 -27.2%

SW62 DT 33.7 23.3 -30.9%

SW66 DT 35.4 19.4 -45.2%

SW111 DT 40.9 22.9 -43.9%

SW112 DT 35.4 22.2 -37.3%

Figures and Appendices