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Item Open Access Aircraft Measurements of NOx Over the Eastern Pacific and Continental United States and Implications for Ozone Production(AGU, 1990) Carroll, M.A.; Hastie, D.R.; Ridley, B.A.; Rodgers, M.O.; Torres, A.L.; Davis, D.D.; Bradshaw, J.D.; Sandholm, S.T.; Schiff, H.I.; Karecki, D.R.; Harris, G.W.; Mackay, G.I.; Gregory, G.L.; Condon, E.P.; Trainer, M.; Hubler, G.; Montzka, D.D.; Madronich, S.; Albritton, D.L.; Singh, H.B.; Beck, S.M.; Shipham, M.C.; Bachmeier, A.S.Measurements of NO, NO2, O3, and CO are presented from 13 aircraft flights made over the eastern Pacific Ocean and the continental United States in August and September 1986 during the NASA GTE/CITE 2 program. Measurements of NO by three different groups (two different techniques) and of NO2 by three different groups (three different techniques) are presented and examined along with calculated NO x (NO + NO2) for correlations with O3, CO, and dew-point temperature (DPT) primarily as a function of air mass category. Median values of NO and NO2 in the marine boundary layer were 4.0 and 10.4 pptv, respectively, and 12.4 and 18.0 pptv in the marine free troposphere. In the continental boundary layer, median values of NO and NO2 were 34.5 and 75.0 pptv, respectively, and 13.0 and 36.0 pptv at altitudes above 3 km in air masses having continental influence. In the maritime NO x data set a negative correlation is often observed between NO x and DPT, while positive correlations were typically observed between NO x and O3 and between NO x and CO. As expected, then, negative correlations were often observed between O3 and DPT and between CO and DPT, along with positive correlations between CO and O3. In the continental data set, positive correlations were typically observed between NO x and DPT, O3, and CO. Additionally, the various air masses were examined with respect to regions of net ozone production or net ozone destruction. In all but one case in the marine boundary layer, model calculations indicate that there is significant ozone destruction. In the continental boundary layer, however, calculations indicate significant ozone production. In the middle free troposphere at 5 ± 1 km, the in situ ozone formation was most often nearly in balance with ozone destruction.Item Open Access Atmospheric Concentrations and Temporal Variations of C1-C3 Carbonyl Compounds at Two Rural Sites in Central Ontario(Elsevier, 1991) Shepson, P.B.; Hastie, D.R.; Schiff, H.I.; Polizzi, M.; Bottenheim, J.W.; Anlauf, K.; Mackay, G.I.; Karecki, D.R.Measurements of formaldehyde, acetaldehyde, acetone and propionaldehyde concentrations were made at two rural sites in central Ontario. One site (at Egbert, Ont.) is located ≈60 km northwest of Toronto, while the other site (at Dorset, Ont.) is ≈150 km northeast of the Egbert site. Measurements were made using a modified version of a derivatization technique in which sample air is pumped through Teflon tubes packed with silica gel that is coated with 2,4-dinitrophenylhydrazine (DNPH). The product hydrazones were separated and quantified using HPLC. Quantitative determinations of formaldehyde, acetaldehyde and acetone were made for 49 and 47 samples at the Dorset and Egbert sites, respectively, between 25 July and 30 August 1988. The average concentrations determined at the Dorset site for formaldehyde, acetaldehyde, and acetone were 1.6, 0.46 and 1.8 ppb, respectively, and for the Egbert site the corresponding averages were 1.8, 0.57 and 1.6 ppb. A set of 10 samples from the Egbert site were analysed for propionaldehyde yielding an average concentration of 0.03 ppb. The formaldehyde measurements were compared with measurements made at the same time using Tunable Diode Laser Absorption Spectroscopy. The observed concentrations reported here are compared with previously reported measurements of these species and interpreted in terms of atmospheric variables (e.g. meteorology, concentrations of precursor hydrocarbons) influencing their concentrations.Item Open Access An Intercomparison of Airborne Nitric Acid Measurements During CITE-2(AGU, 1990) Gregory, G.L.; Hoell Jr., J.M.; Huebert, B.J.; van Bramer, S.E.; LeBel, P.J.; Vay, S.A.; Marinaro, R.M.; Schiff, H.I.; Hastie, D.R.; Mackay, G.I.; Karecki, D.R.Results from an airborne intercomparison of techniques to measure tropospheric levels of nitric acid are discussed. The intercomparison was part of the National Aeronautics and Space Administration’s Global Tropospheric Experiment and was conducted during the summer of 1986. Instruments intercompared included a denuder tube collection system (DENUDER) with chemiluminescent detection, a nylon filter collection system (FILTER) with ion chromatography detection, and a tunable diode laser (TDLAS) multipath absorption system. Intercomparison of investigators’ calibration standards were also performed as part of the test protocol. While results were somewhat ‘‘soft’’ and data sparse, these tests suggested that the TDLAS measurements might be high compared to the other techniques. Airborne intercomparisons were conducted predominately in the free troposphere and included encounters with marine and continental air masses. While the intercomparisons included mixing ratios to 1000 parts per trillion by volume (pptv), the majority of the results were for mixing ratios of <300 pptv. The TDLAS participated in an intercomparison of NO2 instruments (major focus) that was also conducted during the same flights. As a result the TDLAS data set is limited. Further, a significant fraction of the nitric acid measurements were below the TDLAS detection limit (75 pptv as configured for these tests). While the lack of simultaneous measurements from the three instruments limits the conclusions that can be drawn, it is clear that there can be substantial disagreement among the three techniques, even at mixing ratios above their respective detection limits. Equally clear is that at mixing ratios below 150 pptv there is very little correlation between their results. Based on these observations, an overall conclusion from the intercomparison is that none of the HNO3 techniques can be identified to unambiguously (e.g., 20% accuracy) provide measurements of HNO3 at levels often encountered in the free troposphere (e.g., 100 pptv). However, at the more elevated levels of HNO3 (e.g., >150 pptv), both the FILTER and DENUDER techniques reported the same levels of nitric acid, while as suggested by the results from the standards intercomparison, the TDLAS reported higher nitric acid values than the other two techniques. ©American Geophysical Union 1990Item Open Access An Intercomparison of Airborne Nitrogen Dioxide Instruments(AGU, 1990) Gregory, G.L.; Hoell Jr., J.M.; Carroll, M.A.; Ridley, B.A.; Davis, D.D.; Bradshaw, J.; Rodgers, M.O.; Sandholm, S.T.; Schiff, H.I.; Hastie, D.R.; Karecki, D.R.; Mackay, G.I.; Harris, G.W.; Torres, A.L.; Fried, A.Results from an airborne intercomparison of techniques to measure tropospheric levels of nitrogen dioxide (NO2) are discussed. The intercomparison was part of the National Aeronautics and Space Administration’s Global Tropospheric Experiment and was conducted during the summer of 1986. Instruments intercompared included a two-photon nitric oxide (NO) laser-induced fluorescence system with laser photolysis of NO2 to NO, and NO/O3 chemiluminescence detector using FeSO4 for conversion of NO2 to NO, and NO/O3 chemiluminescence detector with arc lamp photolysis of NO2 to NO, and a tunable diode laser multipath absorption system. All intercomparisons were for NO2 mixing ratios of <200 pptv with most at mixing ratios of <100 pptv. The FeSO4 converter was found to convert peroxyacetyl nitrate (PAN) to NO, resulting in NO2 values a factor of 2–3 higher than reported by the other techniques. Thus the FeSO4 converter data are excluded from the analyses. Intercomparison data were analyzed in various mixing ratio ranges. Good correlation was observed between the remaining three instruments for those data sets which included mixing ratios to 100 or 200 pptv, showing on the average a 30–40% level of agreement among the techniques. However, when the data were restricted to mixing ratios of <50 pptv, little correlation among the measurements was observed. Even though correlations were poor at mixing ratios of <50 pptv, the tunable diode laser system tended to be high compared to data reported by the two-photon laser and arc lamp chemiluminescence systems, and agreement between the latter two instruments was generally better than 20 pptv with an equal tendency for one to be high relative to the other. © American Geophysical Union 1990Item Open Access Measurement of Gas Phase Hydrogen Peroxide in air by Tunable Diode Laser Absorption Spectroscopy(AGU, 1986) Slemr, F.; Harris, G.W.; Hastie, D.R.; Mackay, G.I.; Schiff, H.I.Tunable diode laser absorption spectroscopy has been applied to the determination of gas phase hydrogen peroxide in ambient air with sub-ppbv (parts per billion by volume) detection limits for measurement times of the order of minutes. The methods for calibrating the instrument and for assuring the absence of spectroscopic and sampling interferences at the level of our present detection limits are described. Ambient air monitoring with our system indicates that the hydrogen peroxide mixing ratio is often < 0.3 ppbv. Five-minute average mixing ratios of up to 2.9 ppbv have been measured at sites in southwestern Ontario, Canada, during the summer months of 1984 and 1985, while the highest 1-hour average value observed was 2.1 ppbv.Item Open Access Ratios of Peroxyacetyl Nitrate to Active Nitrogen Observed During Aircraft Flights Over the Eastern Pacific Ocean and Continental United States(AGU, 1990) Ridley, B.A.; Shetter, J.D.; Grandrud, B.W.; Salas, L.J.; Singh, H.B.; Carroll, M.A.; Hubler, G.; Albritton, D.L.; Hastie, D.R.; Schiff, H.I.; Mackay, G.I.; Karecki, D.R.; Davis, D.D.; Bradshaw, J.D.; Rodgers, M.O.; Sandholm, S.T.; Torres, A.L.; Condon, E.P.; Gregory, G.L.; Beck, S.M.During August and September 1986, 11 aircraft flights were made over the eastern Pacific Ocean and continental United States. The suite of observations included simultaneous measurements of peroxyacetyl nitrate (PAN) and active nitrogen (NOx=NO+NO2). At altitudes of 4.5–6.1 km in the middle free troposphere, PAN was usually 5–6 times NOx in maritime air masses and 2–4 times NOx in continental air masses. In air masses of tropical origin, or in the marine boundary layer, both PAN and NOx were typically less than 20–30 parts per trillion by volume, and the PAN to NOx ratio was less than one. The observations show that PAN can be a major component of the odd nitrogen budget in the middle free troposphere and strongly reinforce earlier views that the abundance is mainly governed by long-range transport processes including formation during transport and continental boundary layer to free tropospheric exchange of PAN and its precursors. Unlike reservoir HNO3, PAN can be transformed to active nitrogen and peroxy radicals by a variety of physical atmospheric processes that lead to air mass warming. Since NOx plays a critical role in determining photochemical O3 production, which in turn determines the oxidative power of the atmosphere, the observed large ratios of reservoir PAN to active NOx imply an important photochemical and dynamical role for PAN in the eastern Pacific remote free troposphere.Item Open Access The Southern Ontario Oxidant Study (SONTOS): Overview and Case Studies for 1992(Elsevier, 1996) Reid, N.W.; Niki, H.; Hastie, D.R.; Shepson, P.B.; Roussel, P.B.; Melo, O.T.; Mackay, G.I.; Drummond, J.; Schiff, H.I.; Poissant, L.; Moroz, W.The southern Ontario oxidant study (SONTOS) is one of the scientific responses to the problem of ozone exceedences in the Windsor/Quebec City corridor, the strip extending from Windsor in the extreme southwest of Ontario, along the north shores of Lake Erie and Lake Ontario and down the St Lawrence valley. This corridor includes the two major metropolitan areas of Toronto and Montreal and experiences more exceedences of the Canadian ozone guideline per year than any other part of the country. The overall objective of SONTOS is to elucidate the factors which lead to these high levels. The study design is based on intensive measurements made at a site to the NNW of Toronto, with supplementary measurements at other sites and on board an aircraft. This paper, and the seven which follow, describe and interpret the measurements made in the summer of 1992. Although this summer was noteworthy for generally very low ozone concentrations, a number of interesting observations have been made which have a bearing on the oxidant phenomenon in southern Ontario. In particular, this paper describes two specific events. In one, which occurred on 6 August 1992, the intensive measurement site experienced the impact of a polluted air mass, which had apparently travelled to the site from Toronto, by way of Lake Ontario. This case has been contrasted with an event in the last week of August, in which large-scale, organised southwesterly flow led to the conditions which more typically give rise to widespread ozone episodes in the province. Events similar to the 6 August episode occurred on several occasions during the study period, and underline the very important role of the Great Lakes in ozone transport and delivery in southern Ontario.Item Open Access A Tunable Diode Laser System for Aircraft Measurements of Trace Gases(AGU, 1990) Schiff, H.I.; Karecki, D.R.; Harris, G.W.; Hastie, D.R.; Mackay, G.I.The advantages of tunable diode laser absorption spectrometry (TDLAS) for measuring trace atmospheric gases are universality, positive identification, good sensitivity, and rapid response time. A TDLAS system is described which is capable of making measurements on board an aircraft. The instrument was employed during the Chemical Instrumentation Test and Evaluation (CITE) 2 program to measure NO2, on 11 flights and HNO3, on five flights. Detection limits were determined to be 25 parts per trillion by volume [pptv] for NO2 and 75 pptv for HNO3 with response times of 3 min. This was sufficient to permit measurements of NO2 in the free troposphere and HNO3, in the continental boundary layer a significant fraction of the time.