** Created 12 September, 2018 by Dr Popoola Olalekan email: oamp2@cam.ac.uk alternative email: oampopoola@gmail.com This meta file describes the data format in each folder. Except otherwise noted, dates are in UTC in the format dd/mm/yyyy hh:mm:ss, CO, NO, NO2 and Ox are expressed in mixing ratios as ppbv, CO2 is in ppmv. Wind speed (ws) are in m/s and wind direction (wd) are in degrees. 1. Folder "Fig2_FigS8_S1" contains csv files for the 20 sec absolute data for the species CO, NO, Ox and CO2 for the 18 sites presented in Fig2 & FigS8, and one pdf file of the R script used for the bivariate plots presented in FigS1.The NO and CO2 data are used for to produce the polar bivariate plots in Fig. S1. 2. Folder "Fig3" is made up of two csv files for NOx and CO2 comparison tests. 3. Folder "Fig4" contains one csv file for SNAQ data at sites 47 & 48. 4. Folder "Fig5" has three csv files for SNAQ 20 sec absolute CO data at sites 19, 29 & 50 over a three hour period on 24 October, 2012. 5. Folder "Fig6_S3_FigS4" contains two csv files for hourly data at the two sites (high and low pollution sites). 6. Folder "Fig7" contains one csv file for hourly data at site29 for both snaq and model (refined and unrefined). 7. Folder "Fig9" has one csv file: hourly averaged CO2 and NO2 data for the absolute, local and non-local data. 8. Folder "Fig10" contains three files: two csv files for the hourly local and non-local data at site29, and one pdf file of the R script used for the bivariate plots. 9. Folder "Fig11" has three csv files: the non-local NO2, site 29 local NO2 and site 30 local NO2. Note NO2 units are expressed as µg/m3. These files were used to create the diurnal average plots. 10. Folger "Fig12" has 19 csv files; 17 files for hourly local NO2 model vs SNAQ data, 1 for hourly local NO2 model vs SNAQ at LHR2 and 1 for hourly absolute and local NO2 for Ref and SNAQ at LHR2. These are used to create the average and 3 sigmal plots in Fig5. 11. Folder "FigS2" has three csv files for SNAQ 20 sec absolute CO2 data at sites 19, 29 & 50 over a three hour period on 24 October, 2012. 12. Folder "FigS5&TableS1" contains three csv file for hourly data at site29, site30 & site47 for both snaq and model (refined). These are used to generate a scatter plots of CO2 to CO, NO, NO2.The slopes of these plots are used for the emission indices in table S1.