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NOx to NO2 Calculator


This calculator allows users to derive NO2 from NOx wherever NOx is predicted by modelling emissions from roads. The calculator can also be used to calculate the road component of NOx from roadside NO2 diffusion tube measurements. Local authorities are advised to use the latest version of the tool for all future work that is based upon use of the 2018 reference year background maps and the EFT v10.1 onwards.

The current version of the calculator (v8.1) should only be used with the 2018 Reference Year Background Maps and the Emissions Factors Toolkit v10.1, and can be used for years 2018 to 2030. Guidance on how to use the NOx to NO2 Calculator is available in the Background Maps User Guide provided below.

Current Version


NOx to NO2 Calculator v8.1

Released: August 2020 (XLSM, 3.2MB)

Background Maps User Guide

Released: August 2020 (PDF, 1.1MB, 44 pages)


Version 8.1 updates version 7.1 to use updated estimated regional concentrations and updated f-NO2 values from NAEI 2017 projections that are consistent with the 2018 base year LAQM background maps. It also provides the capability to include user defined f-NO2 values in both the NOx to NO2 and NO2 to NOx conversion calculations. This version covers the years 2018 to 2030.

The basis for the f-NO2 values and background information for version 8.1 is as follows:

  • Values of f-NO2 have been developed from factors in the EMEP/EEA Emissions Inventory Guidebook (2016) for different vehicle types and Euro standards and recent studies by Carslaw et al. (2016) ‘Have vehicle emissions of primary NO2 peaked?’ (Faraday Discuss., 2016, 189, 439).
  • All the factors are taken from the Guidebook, except those for Euro V and VI HGVs and buses which are based on Carslaw et al. from measurements of NO2/NOx ratios using roadside remote sensing. The Carslaw et al. study suggests lower f-NO2 factors for Euro V and VI HGVs and buses than previously estimated.
  • The factors for individual vehicle types have been weighted according to the contribution each vehicle type makes to total NOx emissions from traffic in each of these area and road types to provide factors for overall UK traffic, urban traffic, non-urban traffic and traffic in London.
  • The background maps and the NOx emission weightings on the f-NO2 factors are derived from NAEI emission projections, as used in the 2018 baseline projections.
  • Fleet turnover has been estimated using information derived from DfT and London-specific information on the bus and taxi fleet provided by TfL, with the central London Ultra Low Emission Zone included from 2019.
  • The NOx emission factors are based on COPERT 5. The baseline NOx projections include the introduction of Euro standards up to Euro 6/VI, and include the expected impact of the two-stage introduction for diesel cars and LGVs of the new European Real-Driving Emission (RDE) regulations.
  • Further details on the derivation of f-NO2 factors in the NAEI are given in the “Primary NO2 Emission Factors for Road Vehicles“, published in March 2019.


Please Note: Users of the updated LAQM tools should be aware that the projections in the 2018 reference year background maps and associated tools are based on assumptions which were current before the Covid-19 outbreak in the UK. In consequence these tools do not reflect short or longer term impacts on emissions in 2020 and beyond resulting from behavioural change during the national or local lockdowns.

Previous Version


NOx to NO2 Calculator Version 7.1 

Released: April 2019 (XLS, 3.2MB)


Whilst local authorities are advised to use the latest version of the NOx to NO2 Calculator for all future work, in support of ongoing work, the previous version of the NOx to NO2 Calculator has been provided.

For older versions of the NOx to NO2 Calculator, or details on the basis for the f-NO2 values and background maps utilised in older versions, please contact the LAQM Helpdesk for further assistance.

LAQM Helpdesk
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