The isotopic composition of carbon monoxide at Montauk Point, Long Island

We present the seasonal cycle of the stable isotopes of CO (¹³CO and C ¹⁸O) along with CO concentration from samples collected weekly at Montauk Point, Long Island, between October 1996 and October 1997. The seasonal cycle of the stable isotopes is similar in shape to studies carried out at more pristine locations, but the isotopic values are quite different as a result of differing relative strengths of seasonal sources. We also observe a fairly strong correlation between oxygen-18 and CO concentration, indicating one predominant source in this region (fossil fuel combustion). The observed isotopic seasonality can help constrain relative source strengths as certain sources have characteristic isotopic signatures. We use a simple isotope chemistry model to simultaneously solve for the relative strengths of the major sources during the sampling period. We find that fossil fuel combustion is the most predominant source, with only small contributions from nonmethane hydrocarbon oxidation and biomass burning, even during the summer and fall months.