Variation of Carbon Monoxide Concentrations as Related to Sampling Interval, Traffic and Meteorological Factors

Abstract

Diurnal variations of carbon monoxide concentrations and traffic density, exemplified in the literature as common for urban areas, were observed at “curb-side” studies in Nashville, Tenn., and Cincinnati, Ohio. A new technique is suggested for evaluating the effect of changes in traffic density on CO concentrations which may be useful for urban planning purposes and for appreciating the role wind speed can play to modify these assessments. Peak to mean ratios of CO concentrations at Cincinnati were in the same range, 2:1–3:1, as those reported in single-source experiments in open terrain in which the source and receptor were located at the same height. In both cities, the decrease of the average ratios, χ_τ/χ₆₀, (maximum short-period CO concentrations within the hour to the mean value over the hour) with increasing τ, proceeds at a somewhat slower rate for τ > 3 min than in single source cases. Multiple and indefinite sources of CO in the immediate area of the urban sampling sites undoubtedly account for this by providing an atmosphere which is never entirely free of CO contamination.