Evaporative tra$c hydrocarbon emissions, tra$c CO and speciated HC tra$c emissions from the city of Athens

Quasi-continuous measurements of NO x , CO and C 5 }C 12 hydrocarbons made during the MEDCAPHOT-TRACE experiment in a street canyon with heavy tra$c load were used to estimate the CO/NO x and 36 individual NMHC/NO x tra$c emission ratios in the Athens basin. A tra$c emission inventory has been compiled for Athens and aspects of this inventory were tested against measurements. The results indicate that although the main features of the 9:00 to 15:00 variations of the NMHC/NO x and CO/NO x inventory emission ratios are in agreement with observations, during the rest of the day the "ne structure of the variations of these ratios cannot be accurately predicted by the inventory. Comparison of pollutant emission ratios derived from ambient measurements with emission ratios predicted by existing inventories for Athens reveals serious discrepancies. Further, the experimental results and theoretical considerations indicate that the speciation of evaporative emissions changes with increasing ambient temperature in favour of the most volatile HC species, thus changing the speciation of tra$c emissions during the course of the day. This is an aspect that is not taken into account in present urban photochemical modelling inventories. ( 1999 Published by Elsevier Science Ltd. All rights reserved.