Abstract
Hourly measurements at an urban airport and at a rural laboratory have been used in a study of Chicago area urban-rural humidity differences. Although the relative humidity was usually lower in the city than in the country, largely a consequence of the urban heat island, this was not the case for parameters less sensitive to temperature. On average, urban vapor pressures and dew points were less than rural ones only in the forenoon and spring afternoons. Urban-rural differences in these two variables also varied with ambient wind speed, cloud cover and moisture stratification in the surface boundary layer.
