"SCOPE AND SUMMARY OF PROGRAM The current program consisted of three distinct phases involving analytical methods development@ field studies@ and analysis and interpretation of the field study results. The analytical development phase of the program involved developing or refining state-of-the-art techniques for the determination of ambient levels of PAN@ NH3@ HNO3@ and NH4+. The field sampling phase of the program consisted of 5 weeks of air monitoring and particulate collections in St. Louis@ Missouri@ and 5 weeks in West Covina@ California. In addition to the chemical measurements mentioned above@ NO@ NO2@ O3@ NO2@ NO3 and C@H@N were determined. Meteorological variables including wind speed@ wind direction@ temperature@ relative humidity@ and solar intensity were also monitored continuously. In St. Louis@ several rainfall samples were collected and analyzed for trace nitrogen compounds. Vertical NOx sampling using a fixed-wing aircraft was conducted during several days in St. Louis. Composite dust samples were collected in both cities and analyzed for nitrogen constituents. Silver-membrane filter samples were also taken in West Covina for analysis by electron spectroscopy chemical analysis (ESCA). The analysis and interpretation phase of the program involved statistical analysts of the data from both cities with the purpose of deriving relationships among chemical and meteorological parameters in order to help us improve our understanding of the fate of nitrogen oxides. Although the analysis and interpretation of our results will continue into another year@ there are a number of observations and tentative conclusions which stand out at this time. Several of these are summarized below. During the early phases of this program@ two techniques for monitoring nitric add were developed. The first of these is a continuous procedure which utilizes a modified@ acid-detecting coulometric instrument. The second technique is an integrating method wherein nitric acid in the air is separated from nonvolatile particulate nitrate and collected in solution. The solution is subsequently analyzed for nitrate. These two methods have been employed successfully in smog chamber research and in the field studies described in this report. Based on these two techniques@ nitric acid was observed in the atmospheres of both St. Louis and West Covina. The nitric acid concentration was found to vary from less than 1 ppb to greater than 30 ppb on an hourly average basis. In order to derive a ""balance"" between nitrogen oxide reactant and NOx reaction products@ it was necessary to determine the fraction of NOx which was converted to products or removed from the atmosphere at any given time. where (CO/NOx) emission inventory is the based on emissions inventory estimates and (CO) and (NOx) measured are the actual concentrations of CO and NOx at any point in time. The first term on the right hand side of the equation can be thought of as a predicted NOx concentration based on the estimated emissions ratio of CO and NOx and the measured CO concentration at any given time. The assumption is made here that over short time periods (several hours) CO is inert and can be used as a tracer for NOx concentration. Substracting the actual measured NOx concentration from the predicted concentration yields the term ""NOx Loss"". Based on our ""NOx Loss"" calculations it appears that the mechanisms by which the nitrogen oxides are removed from the atmosphere involve relatively slow processes. In West Covina@ the greatest loss of nitrogen oxides was observed during midafternoon on high photochemical smog days. This portion of the ""NOx Loss"" profile was highly correlated with ozone concentration. If certain assumptions are accepted@ the afternoon or photochemical loss of nitrogen oxides appears to be largely accounted for by the sum of the PAN and nitric acid concentrations. There was some evidence that nitric acid is removed from the air by alkaline-surface glass-fiber filters@ but not by high-purity quartz-fiber filters. If true@ this would mean that much particulate nitrate data collected over the years may have been strongly influenced by gaseous nitric acid. There was also some indication that ozone is transported into the St. Louis region during early morning hours. While the source of this ozone is not yet clear@ there is some evidence that PAN and possibly nitric acid are associated with the nighttime ozone. The program is continuing@ and the second year effort will be devoted in part to further validation and documentation of our nitric acid measurements and in part to further analysis and Interpretation of our first-year field results. Special emphasis in the second year will be placed on expanding our data base to include data collected at the same time by other research groups in the St. Louis and Los Angeles area. Inclusion of these data in our analyses will increase both the scope of the investigation and the accuracy of the results."
API 4264-1974 history
1974API 4264-1974 THE FATE OF NITROGEN OXIDES IN THE ATMOSPHERE - FINAL REPORT