An Ambient Measurement\nTechnique for Vehicle Emission\nQuantification and Concentration Source Apportionment

We develop a new technique called <i>plume regression</i> where fast response instruments located at the roadside are used\nto measure exhaust plumes of passing vehicles. The approach is used\nto generate highly disaggregated vehicle emissions information by\nvehicle type, which compares well with traditional vehicle emission\nremote sensing. Additionally, the technique provides valuable new\ninformation on ambient concentration source apportionment by vehicle\ntype. The technique is flexible enough to consider a wide range of\nair pollutants and be deployed at roadside ambient monitoring locations.\nThe new approach is used to quantify emissions and concentration source\napportionment for ammonia (NH<sub>3</sub>) and nitrogen oxides (NO<sub><i>x</i></sub>). We find that emissions of NH<sub>3</sub> are generally very well controlled from diesel vehicles including\nthose with selective catalytic reduction systems that use NH<sub>3</sub> to reduce emissions of NO<sub><i>x</i></sub>. By contrast,\ngasoline passenger cars are shown to be the dominant contributor to\nNH<sub>3</sub> emissions, which increase with vehicle mileage. Average\nfuel-specific NH<sub>3</sub> emission factors for gasoline vehicles\nrange from 0.3 to 1.2 g kg<sup>–1</sup>, while diesel vehicle\nemission factors remain below 0.06 g kg<sup>–1</sup>, with\nthe exception of Euro VI buses with the latest regulatory provisions\n(0.5 g kg<sup>–1</sup>).