We have determined the concentrations of carbonyl sulfide (OCS), dimethylsulfide, and carbon disulfide (CS 2) in the breath of a group of cystic fibrosis (CF) patients and one of healthy controls. At the detection sensitivity in these experiments, room air always contained measurable quantities of these three gases. For each subject the inhaled room concentrations were subtracted from the timecoincident concentrations in exhaled breath air. The most significant differences between the CF and control cohorts in these breath-minus-room values were found for OCS. The control group demonstrated a net uptake of 250 ؎ 20 parts-per-trillion-byvolume (pptv), whereas the CF cohort had a net uptake of 110 ؎ 60 pptv (P ‫؍‬ 0.00003). Three CF patients exhaled more OCS than they inhaled from the room. The OCS concentrations in the CF cohort were strongly correlated with pulmonary function. The dimethylsulfide concentrations in breath were greatly enhanced over ambient, but no significant difference was observed between the CF and healthy control groups. The net (breath minus room) CS 2 concentrations for individuals ranged between ؉180 and ؊100 pptv. They were slightly greater in the CF cohort (؉26 ؎ 38 pptv) vs. the control group (؊17 ؎ 15 pptv; P ‫؍‬ 0.04). Lung disease in CF is accompanied by the subsistence of chronic bacterial infections. Sulfides are known to be produced by bacteria in various systems and were therefore the special target for this investigation. Our results suggest that breath sulfide content deserves attention as a noninvasive marker of respiratory colonization.bacterial emission ͉ early detection ͉ Pseudomonas aeruginosa ͉ carbonic anhydrase ͉ mucin sulfation

[1] An extensive set of carbonyl sulfide (OCS) observations were made as part of the NASA Intercontinental Chemical Transport Experiment-North America (INTEX-NA) study, flown from 1 July to 14 August 2004 mostly over the eastern United States and Canada. These data show that summertime OCS mixing ratios at low altitude were dominated by surface drawdown and were highly correlated with CO 2 . Although local plumes were observed on some low-altitude flight legs, anthropogenic OCS sources were small compared to this sink.

Calculations were performed to determine the structures, energetics, and spectroscopy of the atmospherically relevant complexes (HNO 3 )Á(NO 2 ), (HNO 3 )Á(N 2 O 4 ), (NO 3 À )Á(NO 2 ), and (NO 3 À )Á(N 2 O 4 ). The binding energies indicate that three of the four complexes are quite stable, with the most stable (NO 3 À )Á(N 2 O 4 ) possessing binding energy of almost À14 kcal mol À1 . Vibrational frequencies were calculated for use in detecting the complexes by infrared and Raman spectroscopy. An ATR-FTIR experiment showed features at 1632 and 1602 cm À1 that are attributed to NO 2 complexed to NO 3 À and HNO 3 , respectively. The electronic states of (HNO 3 )Á (N 2 O 4 ) and (NO 3 À )Á(N 2 O 4 ) were investigated using an excited state method and it was determined that both complexes possess one low-lying excited state that is accessible through absorption of visible radiation. Evidence for the existence of (NO 3 À )Á(N 2 O 4 ) was obtained from UV/vis absorption spectra of N 2 O 4 in concentrated HNO 3 , which show a band at 320 nm that is blue shifted by 20 nm relative to what is observed for N 2 O 4 dissolved in organic solvents. Finally, hydrogen transfer reactions within the (HNO 3 )Á(NO 2 ) and (HNO 3 )Á(N 2 O 4 ) complexes leading to the formation of HONO, were investigated. In both systems the calculated potential profiles rule out a thermal mechanism, but indicate the reaction could take place following the absorption of visible radiation. We propose that these complexes are potentially important in the thermal and photochemical production of HONO observed in previous laboratory and field studies.