Page 10 - Swale AQMA Feasibility Study April 2020_

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

Model Verification

2.12 It is recommended, following guidance set out in LAQM.TG(16), that the model
results be compared with measured data to determine whether they need
adjusting to more accurately reflect local air quality. This process is known as
verification and reduces the uncertainty associated with local effects on
pollution dispersion and allows the model results to be more site-specific.

2.13 A verification study has been undertaken using local authority monitoring data
from 2018, along Key Street, Keycol Hill and within the existing Newington
AQMA. Full details of this study are included in Appendix B. The model was
found to be under-predicting concentrations, which is not unusual and is likely
the result of the local dispersion environment; an adjustment factor of 2.08
was, therefore, applied to the model results. A separate adjustment factor of
5.74 was applied to the section of Keycol Hill with a slope gradient of greater
6
than 6% (this is the maximum gradient that the current EFT (v9.0) can account
for).

Model Uncertainty

2.14 There are a number of inherent uncertainties associated with the modelling
process, including:

Model uncertainty – due to model formulations;

Data uncertainty – due to inaccuracies in input data, including emissions
estimates, background estimates and meteorology; and
Variability – randomness of measurements used.

2.15 Using a validated air quality model such as ADMS Roads combined with
performing model verification accounts for much of this uncertainty. In
addition, the most detailed available input data is used and reviewed to ensure
accuracy.

9438 AQMA Feasibility Study.docx Date: 20 April 2020 Page 9 of 20