NO3 and NO2 in the mid-pacific troposphere

Spectroscopic measurements from Mauna Loa, Hawaii, yield mixing ratios for NO₃ and NO₂ at night of ∼0.3 and ∼30 ppt, respectively, at 3 km altitude in the free troposphere. The mixing ratio of NO₂ in November is close to that measured earlier in June, and no significant seasonal change is apparent. The mixing ratio of NO₃ is far below that expected, implying the existence of a scavenger for NO₃; the scavenging rate (∼10^-3 s^-1) is close to that found earlier in the Colorado mountains. While the scavenger remains unidentified, it appears to be a well-mixed and long-lived atmospheric component. It is not known whether the scavenger acts as a sink for NO_x or whether it merely sequesters it until the following day.