Trajectories and related variations in the chemical composition of air for the Mauna Loa observatory during 1991 and 1992

Isentropic 10-day back trajectories are computed each day for the fall 1991 and winter, spring, and summer 1992 intensives of the second Mauna Loa Observatory Photochemistry Experiment (RILOPEX 2). The trajectories are computed on an isentropic surface at the approximate height of the Mauna Loa Observatory (MLO). Trajectory variations on the daily, as well as annual timescale, are documented and compared to trajectory climatologies for Hawaii. During MLOPEX 2 the Pacific anticyclone was consistently farther west than normal, with important consequences for the computed trajectories. The concentrations of ozone, total reactive oxidized nitrogen, water, methyl nitrate, carbon monoxide, acetylene, radon, and peroxyacetyl nitrate (PAN) measured at MLO are examined in relation to trajectory characteristics on the daily and annual timescales. During the fall intensive and the summer intensive, changes in trajectory characteristics are related, in a broad sense, to changes in the measured concentrations of the above species; during the winter and especially the spring intensives, the trajectories prove to be poor indicators of the measured concentrations. For most species the seasonal variation in the computed trajectories does not satisfactorily explain the annual cycle in their measured concentrations.