Previous works on real-world vehicle emission characteristics have mainly focused on the influences of fuel, speed, vehicle type, elevation, and other factors on vehicle emission quantity and components. However, few studies have investigated the transient trend of automotive exhaust emissions through on-road measurements. The key objective of the present paper was to examine the transient characteristics of exhaust emissions from different vehicle types on the roads of Tianjin. To achieve the goal, a portable emission measurement system (PEMS) was employed to monitor emissions from selected test vehicles—private cars, passenger vehicles, and cargo vehicles. It was found that the high-emission points of test vehicles were mainly distributed in two regions: the high-speed region (speed > 70–90 km/h, vehicle-specific power (VSP) > 0 kW/t) and the medium-speed–acceleration region (20–30 km/h < speed < 60–90 km/h, 0 kW/t <VSP < 12 kW/t). The CO, hydrocarbon (HC), NOx, and particulate number (PN) average emission rates in the high-emission points could be 3.15–14.93 times, 1.93–24.89 times, 3.23–6.03 times, and 3.22–30.27 times of those of average emission rates. The HC, NOx, and PN average emission rates of China IV vehicles in the high-emission points were 2.46–4.92 times, 3.56–6.03 times, and 3.22–13.21 times of those of average emission rates, not less than those of China III (1.93–2.52 times, 2.75–3.90 times, and 9.98–22.34 times). Test vehicles mainly emitted nucleation-mode and Aitken-mode particles, and the increase of the PN concentration emission rate in low-speed and high-speed regions was higher than that in the medium-speed region. The exhaust gas recirculation (EGR) + diesel particulate filter (DPF) could effectively inhibit the Aitken output caused by turbocharged intercooler (CIC). The selective catalytic reduction (SCR) might cause more nucleation-mode particles.
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