Estimations of primary nitrogen dioxide exhaust emissions from chemiluminescence NOx measurements in a UK road tunnel Original Research Article

NO and NO2 measurements have been made using the chemiluminescence method from 115 weekdays during the period 4th Jan–10th Sep 2010 in a well characterised, unventilated tunnel on the Leeds Inner Ring Road. Measurements are made at two points in the tunnel and the difference in NO and NO2 was attributed to emissions from vehicles in the tunnel. These data have been used to determine the fraction of NOx (NO + NO2) as primary NO2 (f-NO2) from vehicles using the tunnel. The average value of f-NO2 from 7 am to 7 pm was 0.17 − 0.03+ 0.01 in agreement with estimations from the UK National Atmospheric Emissions Inventory (NAEI). However, during the day there was a reproducible increase in f-NO2 from approximately 0.10 at 7 am to 0.21 at 7 pm which is not reproduced with the current UK vehicle fleet emissions inventories. The increase in f-NO2 can be qualitatively linked to a decrease in the fraction of NOx arising from heavy goods vehicles and buses.