Questions to the Mayor of London – answered at on 16 January 2019.
The methodology used by The Real Urban Emissions Initiative seems to assume that all of the gaseous hydrocarbons measured are propene (C3H6) given the equation on page 4 which states:
CHr + m (0.21 O2 + 0.79 N2) aCO + bH2O + c (C3H6 + unmeasured C3H6) + dCO2
+ eNO + fNO2 + (0.79m - (e + f)/2) N2
Do you know the reasoning behind this assumption that all of the hydrocarbons measured were C3H6 and that none were due to other chemical species such as C4H8, C2H6 or CH4?
Please see The Real Urban Emissions (TRUE) Initiative’s study, ‘Determination of real-world emissions from passenger vehicles using remote sensing data’ (https://www.trueinitiative.org/media/596931/true_remote_sensing_data.pdf) and refer to footnote 10 on page four for an explanation.
As this report is not a Greater London Authority report, TRUE Initiative would be best placed to provide further information. Their contact details can be found in the report referenced above.