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An aircraft-based measurement campaign was conducted during the summer of 1996 in the vicinity of Toronto, Canada. The objective of the campaign was to assess the errors in a particular emission inventory used by three-dimensional air quality models. Measurements of NO 2 and hydrocarbons were made both upwind and downwind of Toronto, on days with strong synoptic-scale flow from a west to northerly direction. The chemical composition of the background airmass on these days was typical of unpolluted continental air. Measurements have been compared with the output from an on-line air quality model (MC2-AQ) run at 5 km resolution and suggest that emissions of NO x from Toronto are well described in the emission database, though evidence that NO x emissions are underestimated for suburban regions surrounding Toronto was found. In general, no significant underestimation of hydrocarbon emissions was found, though emissions of the model propane species, which includes acetylene and benzene, was underestimated by at least a factor of two.

Very rapid increases in the concentrations of ozone and ozone precursors, in the late afternoon, have been observed at a rural and an urban site in southern Ontario. Ozone concentration increases of 30 ppbv in a few minutes have been observed. These increases occur simultaneously with the arrival of a Lake Ontario lake breeze front as identified from meteorological measurements and visible satellite imagery. This indicates that polluted air masses from over Lake Ontario are being transported inland by the lake breeze. Aircraft measurements of ozone, NOx, and hydrocarbons show such an air mass moving inland. Chemical measurements at the sites show that the polluted air masses are not of local origin, but are of similar age to those regularly encountered in rural areas.

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.

A highly selective and sensitive detector for measuring organic nitrates in atmospheric air samples has been developed. This detector is based on the luminol chemiluminescence-based detection of NO 2 produced by postcolumn thermal decomposition of organic nitrates. Determination of the relative detector sensitivities to C 3 -C 6 alkyl nitrates, α,β-hydroxy nitrates, α,β-dinitrates, and several mono- and multinitro aromatic compounds as well as N-nitrosodimethylamine has been conducted. The detector is shown to produce one NO 2 per molecule at a pyrolysis temperature of 350 o C, yielding identical sensitivities for alkyl and hydroxy nitrates, consistent with the known thermal decomposition pathway and thermal lifetimes at this temperature

A gas chromatographic technique for trace level detection of peroxyacetyl nitrate (PAN) that relies on postcolumn chemical amplification as a means of improving the detection limit has been developed. The GC detector is based on luminol chemiluminescence detection of NO 2 . PAN eluting from the chromatographic column is thermally decomposed, resulting in a free-radical chain reaction in which NO is converted to NO 2 , using CO as a chain carrier. The system operates at optimized carrier gas NO and CO concentrations of 6 ppm and 8%, respectively

A 24 day intercomparison study of peroxyacetyl nitrate (PAN) measurement was conducted in Egbert, Ontario, in February–March 1989. Two GC/ECD systems and one GC using a luminolchemiluminescence based detection device were involved. To separate the influence of calibration errors vs possible chromatographic interferences, a series of laboratory standards (gaseous PAN concentrations determined by either i.r. or by chemiluminescence) were exchanged. For all three GCs the results of analysis of standard samples were within ±25% of the standard concentration. For ambient air PAN measurements (concentrations ranging from 0.15 to 2 ppb), plots of each set of measurement data regressed against those of the other two techniques were obtained. Linear regression of the data from ambient air analysis for the two GC/ECD systems yielded a slope and intercept of 1.14±0.01 and −0.03±0.05, respectively (r = 0.995). The plot of the Luminol-based GC against the AES GC/ECD yielded a slope of 1.08±0.03 and an intercept of 0.08±0.24 (r = 0.864). The results demonstrated the reliability of the chemiluminescence calibration technique, and indicated that the luminol-based PAN measurement device can yield accurate and sensitive measurements of ambient PAN concentrations.

Small battery-powered instruments for the sensitive detection of nitrogen dioxide (NO2), and ozone (O3) are described. Because of their portability, they are ideal for studies of indoor air quality, measurements from aircraft, and other mobile platforms where power may be limited. For example, a miniature balloon-borne sonde, based on the chemiluminescence between luminol and NO2 has recently demonstrated the ability to measure ambient mixing ratios of NO2 between ground level and an altitude of 33 km. Recent 'add-on's to the model LMA-3 NO2 analyzer are discussed and the model LOZ-4 ozone monitor is described.

A commercial instrument for measuring PAN (peroxyacetyl nitrate), NO2, and optionally, NOx, is described. It is based on a gas chromatograph (GC), and uses a LuminoxR luminol detector following conversion of the PAN to NO2. A detection limit (based on a peak height of 3 X noise) of 30 pptV is achieved for injections made every five minutes. The instrument is computer driven and contains its own peak integrator and graphics output. No interferences have been identified, including chlorinated hydrocarbons, NO2 and ozone. However, the PAN analog peroxypropanyl nitrate (PPN) is not fully resolved from PAN. The maintenance interval is monthly. The calibration of the instruments is relatively easy: known mixing ratios of NO2 in air are used to calibrate the sample injection system and LuminoxR detector. The passage of PAN through the column and the subsequent conversion of PAN to NO2 has been found to be stable over times of one year, and is reproducible between instruments. Atmospheric measurements for PAN have been carried out for both very polluted environments and very clean environments. The results from a month long formal intercomparison between the LuminoxR PAN and two GCs equipped with electron capture detectors is presented. Those results demonstrate that the luminol based PAN detector can yield accurate measurements of ambient PAN concentrations. A method for calibrating PAN instruments in the field is described.

A detector for the chemiluminescent measurement of NO in background air is described. A large reduction of interferences is achieved by using a stabilized ozone generator which allows operation of the instrument at lower O3 concentrations. Purification and humidification of the O3 stream further reduces interferences and shortens the instrumental clean-up time, which is important for aircraft missions. From a series of laboratory tests and from measurements performed aboard an aircraft it is demonstrated that the remaining interferences are acceptable for measurements in the undisturbed troposphere. In particular, no remnant NO signal is observed in clean air at night. During flight, a detection limit (2σ) of 20 ppt is achieved for a 1 min integration time.

A sensitive chemiluminescent detector for the measurement of NO and NO2 in the unpolluted atmosphere is described. For NO2 measurement, a photolytic converter is employed. For a 200 s integration time, a detection limit (2 σ) of 5 and l0ppt is achieved for NO and NO2, respectively. Interferences are measured and corrected by using a chemical zeroing procedure. Remaining interferences are below the detection limit. The calibration is based on NBS standards and agrees with independent techniques within 10%. Measurements of the vertical profile of NO and NO2 in the troposphere exemplify the performance of the instrument.

MEASUREMENT of nitric oxide (NO) above an altitude of 40 km is of interest because in this region of the stratosphere >70% of the total odd nitrogen (NO+NO2+HNO3+N2O5) is thought to exist as NO, and at 45 km the NO is predicted to be approximately 90% of the total1. This measurement thus provides an important test for odd nitrogen concentrations as predicted by theoretical models for ozone chemistry. Some models show that of the total ozone destruction necessary to explain the observed ozone concentration, approximately 50–70% is due to the odd nitrogen catalytic cycles2.