Abstract
Atmospheric humidity exerts a significant influence on nitrogen oxides emission from gasoline engine, and therefore, it is necessary to establish a correction coefficient with the humidity change. The article describes the determination of correction coefficient and analysis of influence factors by humidity change. It is shown that variations in nitrogen oxides emission levels are mainly affected by the air fuel ratio change and water injection effect. Variation of the atmospheric temperature causes a change of the air fuel ratio. The tests were carried out in California, U. S. A.