The late winter/early spring (February/March, 1994) measurements of Pacific Exploratory Mission-West (PEM-W) B have been analyzed to show latitudinal distributions (45°N to 10°S) of the mixing ratios of reactive nitrogen species (NO, peroxyacetylnitrate (PAN), HNO3, and NOy), ozone, and chemical tracers (CO, NMHCs, acetone, and C2Cl4) with a focus on the upper troposphere. Mixing ratios of all species are relatively low in the warm tropical and subtropical air south of the polar jetstream (≈28°N) but increase sharply with latitude in the cold polar air north of the jetstream. Noteworthy is the continuous increase in reservoir species (PAN and HNO3) and the simultaneous decrease in NOx toward the northern midlatitudes. The Harvard global three-dimensional model of tropospheric chemistry has been used to compare these observations with predictions. In the upper troposphere the magnitude and distribution of measured NOy and PAN as a function of latitude is well represented by this model, while NOx (measured NO + model calculated NO2) is underpredicted, especially in the tropics. Unlike several previous studies, where model-predicted HNO3 exceeded observations by as much as a factor of 10, the present data/model comparison is improved to within a factor of 2. The predicted upper tropospheric HNO3 is generally below or near measured values, and there is little need to invoke particle reactions as a means of removing or recycling HNO3. Comparison between measured NOy and the sum of its three main constituents (PAN + NOx + HNO3) on average show a small mean shortfall (<15%). This shortfall could be attributed to the presence of known but unmeasured species (e.g., peroxynitric acid and alkyl nitrates) as well as to instrument errors. Copyright 1998 by the American Geophysical Union.

Airborne, in situ measurements from PEM-Tropics-A (September/October 1996) are analyzed to show the presence of distinct pollution plumes in the middle-tropical troposphere of the remote South Pacific (10-30°S). These elevated plumes cause a relative maximum at about 5-7km altitude in the vertical distribution of primary and secondary species characteristic of fuel combustion and biomass burning (CO, C2H2, C2H6, CH3Cl, PAN, O3). Similar plumes were also observed at mid-latitudes in the middle troposphere during three flights east of New Zealand (40-45°S). In all, pollution plumes with CO larger than 100 ppb were observed 24 times on seven separate flight days south of the equator. The observed plumes were frequently embedded in very dry air. Ten-day back trajectory analysis supports the view that these originated from the biomass burning regions of South Africa (and South America) and were transported to the South Pacific along long-distance subsiding trajectories. The chemical composition of the southern Pacific troposphere analyzed from the PEM-Tropics-A data is compared with data from the tropical regions of the northern Pacific (PEM-West-A) and southern Atlantic (TRACE-A) during the same Sept/Oct time period. Sizable perturbations in the abundance of ozone and its key precursors, resulting from the transport of pollution originating from biomass burning sources, are observed in much of the Southern Hemispheric troposphere. Copyright (C) 2000 Elsevier Science B.V.

We report the first in situ measurements of hydrogen cyanide (HCN) and methyl cyanide (CH3CN, acetonitrile) from the Pacific troposphere (0-12 km) obtained during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) airborne mission (February-April 2001). Mean HCN and CH3CN mixing ratios of 243 ± 118 (median 218) ppt and 149 ± 56 (median 138) ppt, respectively, were measured. These in situ observations correspond to a mean tropospheric HCN column of 4.2 × 1015 molecules cm-2 and a CH3CN column of 2.5 × 1015 molecules cm-2. This is in good agreement with the 0-12 km HCN column of 4.4 (±0.6) × 1015 molecules cm-2 derived from infrared solar spectroscopic observations over Japan. Mixing ratios of HCN and CH3CN were greatly enhanced in pollution outflow from Asia and were well correlated with each other as well as with known tracers of biomass combustion (e.g., CH3Cl, CO). Volumetric enhancement (or emission) ratios (ERs) relative to CO in free tropospheric plumes, likely originating from fires, were 0.34% for HCN and 0.17% for CH3CN. ERs with respect to CH3Cl and CO in selected biomass burning (BB) plumes in the free troposphere and in boundary layer pollution episodes are used to estimate a global BB source of 0.8 ± 0.4 Tg (N) yr-1 for HCN and 0.4 ± 0.1 Tg (N) yr-1 for CH3CN. In comparison, emissions from industry and fossil fuel combustion are quite small (<0.05 Tg (N) yr-1). The vertical structure of HCN and CH3CN indicated reduced mixing ratios in the marine boundary layer (MBL). Using a simple box model, the observed gradients across the top of the MBL are used to derive an oceanic loss rate of 8.8 × 10-15 g (N) cm-2 s-1 for HCN and 3.4 × 10-15 g (N) cm-2 s-1 for CH3CN. An air-sea exchange model is used to conclude that this flux can be maintained if the oceans are undersaturated in HCN and CH3CN by 27% and 6%, respectively. These observations also correspond to an open ocean mean deposition velocity (vd) of 0.12 cm s-1 for HCN and 0.06 cm s-1 for CH3CN. It is inferred that oceanic loss is a dominant sink for these cyanides and that they deposit some 1.4 Tg (N) of nitrogen annually to the oceans. Assuming loss to the oceans and reaction with OH radicals as the major removal processes, a mean atmospheric residence time of 5.0 months for HCN and 6.6 months for CH3CN is calculated. A global budget analysis shows that the sources and sinks of HCN and CH3CN are roughly in balance but large uncertainties remain in part due to a lack of observational data from the atmosphere and the oceans. Pathways leading to the oceanic (and soil) degradation of these cyanides are poorly known but are expected to be biological in nature.