Validation of ozone precursor measurement through inter-comparison with NOx and CO measurement

Continuous hourly measurement of non-methane hydrocarbons (NMHCs) from C3 to C12 was performed by an automated gas chromatographic (GC) system in downtown Taipei between 20 March 2000 and 12 May 2000. To test the performance this automated GC synchronous measurement of NMHCs with NOx was conducted sharing a common air inlet. Excellent agreement in temporal variation between NMHCs and NOx was observed suggesting that the automated GC measurement was accurately reflecting ambient concentrations of ozone precursors. On two occasions during the monitoring period, abrupt increase in concentrations of gaseous pollutants due to nocturnal radiational inversion occurred at night under stable weather conditions. Improved correlation between different NMHC species for data within these two episodes suggested better air mixing than in other periods. These two events of concentration enhancement driven by temperature inversion were also registered in CO measurement in all EPA air quality stations scattered around Taipei metropolitan area.