Effect of Cold Weather on Motor Vehicle Emissions and Fuel Economy

The effect of soaking temperature on exhaust emissions has been studied using a variety of automobiles representing three different emission control levels and testing them at ambients of 20°C down to -30°C(60°F to -22°F).

It was found that emissions of the three gaseous pollutants demonstrated a mild power relationship with ambient (soaking) temperatures. All regulated pollutants and fuel consumption were higher at -30°C than at 20°C: hydrocarbons (HC) - 3.5 to 9.2 times; carbon monoxide (CO) - 2.4 to 6.4 times; oxides of nitrogen (NO_x) - only 1.1 to 1.4 times; and fuel consumption 1.2 to 1.8 times higher. Analysis of the data has indicated that HC and CO emissions from the cold start phase of the Federal test were the most sensitive to soaking temperature. With NO_x emissions the soaking temperature sensitivity was fairly constant throughout the three phases of the Federal test.

The data also indicate that the temperature sensitivity of both fuel economy and, to a lesser extent, emissions is a function of inertia weight.