Real-time monitoring of individual pollutants and evaluation of OH reactivity in exhaust gas of a mode-driving vehicle utilizing the laser multi-photon ionization technique

Abstract

Real-time monitoring of individual pollutants in the exhaust gas of a mode-driving diesel truck was conducted utilizing the laser multi-photon ionization technique. The volume mixing ratio of benzene, toluene, o-xylene, m-xylene, p-xylene, and phenol were individually analyzed. Temporal variations in these species during the driving mode were successfully observed every second. From the observed mixing ratio and flow rate of the exhaust, the emission factor and OH reactivity of each compound were acquired. As a result, in some cases, unique trends were observed, which could not be captured by monitoring the total hydrocarbons (THC) and/or the mode average of each compound. Especially, a significant phenol level was observed during the high-speed driving period. Additionally, the time series data with a 1-sec resolution were categorized by the driving speed of the vehicle. Consequently, it was found that the emission factor and OH reactivity per travel distance reached the minimum in the middle speed range (50-70 km/h) for the target VOCs. It was confirmed that the real-time analysis of individual compounds in the exhaust gas during the driving mode would be useful.