Using Peroxynitric Acid (PNA) to Assess HOx and NOx Budgets during the NASA ATom Mission

Peroxynitric acid (PNA, HO2NO2 or HNO­­­4) is a key species in the coupling of the HOx (=OH+HO2) and NOx (=NO+NO2) chemical cycles. PNA is formed (and lost) via the association reaction of HO2 and NO2: HO2 + NO2 + M <-> HO2NO2 + M As a result, PNA acts as a significant reservoir and sink for HOx and NOx, particularly at low temperatures, with the potential to greatly impact the atmosphere's oxidative potential. Using chemical ionization mass spectroscopy measurements made during the first few deployments of the Atmospheric Tomography Mission (ATom) aboard the NASA DC-8 aircraft, we present variations in PNA mixing ratios and lifetimes from vertical profiles collected along longitudinal global transects. We compare these measurements, as well as simultaneous measurements of HOx, NOx, and other photochemically active species in the atmosphere, with steady-state calculations and photochemical models to obtain an observationally constrained mass balance and gain insight into the HOy and NOy chemical families. From this combination of observations and modeling, we evaluate the importance of PNA and its role in HO­x and NOx reactivity on a global scale.