A test program was conducted to study the effects of ambient conditions on exhaust emissions from a variety of automobiles. Twenty-six cars, ranging from 1967 models through catalytic converter-equipped prototypes and cars powered by unconventional engines (rotary, Diesel, and stratified charge), were tested at 20 degrees, 50 degrees, 75 degrees and 110 degrees F. Test procedure was the 1975 FTP, but with engine hoods closed and cooling air flow keyed to vehicle speed. HC, CO, NOx, total aldehydes, and reactive hydrocarbons, plus carbon balance fuel economy, were measured. From production cars and catalyst-equipped cars, '75 FTP composite emissions of all three gaseous pollutants were highest at 20F. HC and CO were generally lowest at 75F; composite values were greatly influenced by cold start (Bag 1) emissions. Composite NOx emissions were generally lowest at 110F, and were relatively unaffected by ambient temperature. Fuel economy at 20F was about 10% lower than at 110F. The Diesel and stratified charge cars had low emissions and little temperature sensitivity. Use of air conditioners at 110F caused higher emissions and about 10% lower fuel economy. Reactivity of HC emissions and aldehyde emissions were unaffected by temperature and were lower from catalyst-equipped cars at all temperatures.

"EPA-460/3-74-028-a." "March 1975." "Interagency Agreement Nos. OMSAPC-IAG-007, OMSAPC-IAG-D4-F402, and OMSAPC-IAG-D4-F533"--T.p. "EPA project officer: H. Anthony Ashby"--T.p.