Radiocarbon (14C) measurements to quantify sources of atmospheric carbon monoxide in urban air

Atmospheric air samples were collected during the winter of 1989–1990 in Albuquerque, NM, U.S.A., for radiocarbon (14C) analysis of carbon monoxide (CO). An experimental sample design was prepared to target periods when the concentration of CO exceeds the 9 μl −1 (volume fraction), 8 h National Ambient Air Quality Standard (NAAQS) and during periods of attainment. Sampling sites, time of day, sampling duration, and meteorology were carefully considered so that source impacts be optimal. A balanced sampling factorial design was used to yield maximum information from the constraints imposed; the number of samples was limited by the number of sample canisters available, time and resources. Radiocarbon measurements of urban CO, “clean-air” CO background from Niwot Ridge, Colorado, average (wood) logs and oxygenated-gasolines were used in a three-source model to calculate the contribution of wood burning to the total atmospheric CO burden in Albuquerque. Results show that the estimated fractional contribution of residential wood combustion (Θ′Rwc) ranged from 0 to 0.30 of CO concentrations corrected for “clean-air” background. For these same samples, the respective CO concentrations attributed to wood burning range from 0 to 0.90 μmol mol−1 (mole fraction), well below the NAAQS. In all cases, fossil CO is the predominant source of ambient CO concentrations ranging from 0.96 to 6.34 μmol mol−1 A final comment is made on the potential of fossil CO measurements as an indirect tracer of atmospheric benzene, relevant to exposure risk estimates of motor vehicle emissions and occupational health and safety standards.