Temporal Variations in CO2 in Air in Pasadena, California
S. Newman and E. Stolper
California Institute of Technology, Pasadena, CA 91125; 626-395-6474, E-mail: firstname.lastname@example.org
How does an urban environment modify the global cycle of observed atmospheric CO2? To address this question, we have studied CO2 since 1998 on the Caltech campus and compared the observed temporal variations with relatively local clean air data from La Jolla (http://scrippsco2.ucsd.edu/data/ljo.html). Time series analysis of daily [CO2] and isotopic composition Caltech data reveal periodicities at 1 and 0.5 year and 7 days. This last period is not observed in La Jolla. In addition, the δ13C pattern is inverted in Pasadena relative to that at La Jolla, and there is no well-defined seasonal variation in CO2 mixing ratio in Pasadena, in contrast to the La Jolla pattern (Figure 1). The seasonal variations in Pasadena reflect the superposition of local contributions of CO2 in Pasadena on global clean air temporal variations. The local contributions are significant: e.g., the total CO2 concentration in Pasadena is ~25 ppm higher than in clean air. Although the typical diurnal variation in CO2 mixing ratio consists of a low [CO2] plateau at about ~10 AM-4 PM PST and a high [CO2] plateau at ~9 PM-3 AM, there are significant variations with season and day of the week (Figure 2). The amplitude of the diurnal variation in Pasadena varies from ~20 ppm in June to ~80 ppm in December. We typically observe a maximum in [CO2] at ~5-9 AM on weekday mornings, which is smaller on weekends and coincides with increased traffic on surface streets in Los Angeles due to weekday morning rush hour. There is no corresponding peak that can be associated with afternoon rush hour.