Total reactive oxidized nitrogen (NO_y) in the remote Pacific troposphere and its correlation with O₃ and CO: Mauna Loa Observatory Photochemistry Experiment 1988

Abstract

As part of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX) total reactive oxidized nitrogen (NOy) was measured during May and early June of 1988 at the Mauna Loa Observatory, the NOAA‐Geophysical Monitoring for Climatic Change Baseline Monitoring Station, located at 3.4‐km elevation on the island of Hawaii. Gold catalytic surface conversion of individual reactive oxidized nitrogen species to NO and subsequent quantification of the NO by NO/O3 chemiluminescence was used to measure the NOy mixing ratio. The NOy abundance at the site was governed by the local downslope/upslope wind systems as well as synoptic‐scale transport. With some exceptions, downslope wind brought air representative of the free troposphere, while upslope winds transported air from below the trade wind inversion to the site. The upslope air masses could be a mix of marine boundary layer air and free tropospheric air modified by anthropogenic and natural emissions from island sources. It was possible to identify free tropospheric air in the downslope flow through meteorological and chemical tracers. Reflecting the remote location, low NOy mixing ratios with median values of 262 and 239 pptv were found in free tropospheric and upslope air masses, respectively. The median NOy levels in free tropospheric air are consistent with airborne NOy measurements made during NASA's Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation (CITE 2) program over the northeastern Pacific Ocean at corresponding altitudes. The median NOy values in upslope flow are significantly higher than those measured in the remote marine boundary layer during CITE 2, reflecting probably the influence of island source and/or mixing of free tropospheric air with boundary layer air. The low correlation found between NOy and tracers of anthropogenic sources, such as carbon monoxide, tetrachloroethylene, and n‐propyl nitrate, in free tropospheric air samples is consistent with a stratospheric or upper tropospheric source for NOy. Simultaneous particulate nitrate (NO3−) measurements suggest that at times not all aerosol NO3− was quantitatively converted to NO by the Au‐surf ace converter technique. These episodes were usually found during upslope flow and were characterized by high sodium concentrations, suggesting that possibly the sodium nitrate contained in these aerosols was not converted efficiently by the Au converter.

First simultaneous measurements of ozone, CO, and NOy at a high‐altitude regional representative site in the central Himalayas

“…This is also in agreement with the conclusion drawn previously. The average CO to NO y ratios were observed to be ~26 in the most polluted and 230 in the cleanest air over rural sites in the U.S. [ Hubler et al ., ; Parrish et al ., ].…”

“…The relationship between CO and NO y can also be used as a tracer of anthropogenic influence in different air masses [Parrish et al, 1991;Hubler et al, 1992;Stohl et al, 2002;Zellweger et al, 2003]. As the air mass ages, CO levels are expected to increase due to longer lifetime as compared to short-lived NO y .…”

Trace gas composition of midlatitude cyclones over the western North Atlantic Ocean: A conceptual model

“…However, these additional NO y sources are relatively small compared to surface emissions, and the result is much less NO y in the middle and upper troposphere than in the lower troposphere. The clean free troposphere has a positive ozone/NO y slope independent of stratospheric influence, but the slope increases as the stratospheric component increases [ Hübler et al , 1992; Koike et al , 1997], as evident in the middle and upper troposphere DA.…”

Occurrence of upslope flows at the Pico mountaintop observatory: A case study of orographic flows on a small, volcanic island

“…They suggested that low‐elevation air could nevertheless impact the station as a result of lifting in thermals. As one example of the apparently complex nature of the upslope flow, Hübler et al [1992] found daytime/nighttime differences in total reactive nitrogen oxides (NO y ) at MLO were smaller than expected if upslope flow simply carried MBL air to the station. They concluded that daytime air at MLO may instead be a mixture of island‐modified MBL air and FT air.…”