Hi, Higher humidity results in lower NOx emissions. Historically, the impact of ambient temperature and humidity on emissions was of, The hourly ambient conditions were derived from data recorded at monitors. Humidity is the measure of the amount of moisture in the air. A psychrometer is an example of a hygrometer. A psychrometer uses two thermometers to measure relative humidity; one measures the dry-bulb temperature and the other measures the wet-bulb temperature.