Impact of altitude on emission rates of ozone precursors from gasoline-driven light-duty commercial vehicles

Vehicle emissions are major precursors for the formation of tropospheric ozone that can have adverse effect on human health, buildings and vegetation. The aim of this study is to investigate the impact of altitude on emission rates of ozone precursors (e.g., CO, NOx and VOCs) from gasoline-driven light–duty commercial vehicles (LDCVs) in three Indian cities (i.e. Delhi, Dehradun, and Mussoorie). Basic equations of the International Vehicle Emission (IVE) model are applied to estimate emission rates from the LDCVs. Topography (altitude) and meteorology (temperature) specific parameters of the IVE model were modified to Indian conditions for estimating emission rates. Unlike NOx, emission rates of CO and VOCs have increased with altitude. For example, CO emission rate has considerably increased from 36.5 g km−1 in Delhi to 51.3 g km−1 (i.e. by ∼41%) in Mussoorie, whereas VOCs emission rate marginally increased from 3.2 g km−1 to 3.6 g km−1. Findings and their implications are important from human health perspective, especially for the people residing in high altitude cities where a peculiar combination of lower oxygen levels and high concentrations of CO and VOCs can adversely affect the public health. Also, increased levels of CO and VOCs at high altitudes may conspicuously influence the chemistry of tropospheric ozone.