Estimation of unidentified non-methane hydrocarbons in urban air based on highly correlated compound pairs

Gas Chromatography coupled with Flame Ionization Detector (GC-FID) is used worldwide for non-methane hydrocarbonsʹ (NMHCs) monitoring. Being a non-selective detector, identification and coelution problems may hamper the reliability of data. An estimation method was developed, based on the correlation of easily measured NMHCs with those unknowns. Correlations were calculated from data obtained with a Gas Chromatograph coupled with a Mass Spectrometer Detector (GC-MSD) after gathering more than 1500 hourly mixing ratio data of 67 NMHCs. The method was developed and validated for an urban area but it may be adapted and applied to other locations. Now it is possible to estimate mixing ratios of some important ozone precursors previously not resolved with the GC-FID, such as 2,2,4-trimethylpentane and 1,2,3-trimethylbenzene. As a result, a six year-long database was enlarged by 34% allowing for a more accurate calculation of the total reactivity and NMHCs’ ozone forming potential.