Nitrogen dioxide photolysis in the Los Angeles atmosphere

Abstract

Atmospheric measurements of k\, the rate of NO2 photolysis, were made in El Monte, Calif., by use of a tubular quartz reactor to measure directly the conversion of NO2 to NO in an N2 atmosphere. A least-squares treatment of the data from September 1975 resulted in the following empirical relationships for predicting k j from standard UV radiometric data. 0°< Solar zenith angle < 40°:(min-1) = 0.079 (1/cos z) + 0.002 X radiometric UV (mW/cm2); 40°< solar zenith angle < 90°: k\ (min-1) = 0.16 (1 -cos z) + 0.088 X radiometric UV (mW/cm2). Ultraviolet intensities corresponding to k\values greater than 0.4,0.3, and 0.2 min-1 can persist for periods of 8, 10, and 12 h, respectively, during the weeks around the summer solstice. Both the high photochemical light intensity observed and its extended time duration indicate that the potential for ozone formation in the atmosphere is greater than utilized in most previous "smog chamber" studies. This result suggests that the application of existing smog chamber data in such areas as solvent reac-

Measurements of the HONO photodissociation constant

“…(1977). A spherical reactor of the type used by Sickles and Jeffries (1975) and a cylindrical (plug flow) reactor were examined (Zafonte et al, 1977). They found the j value measured in the spherical cell to be flow dependent, yielding higher j values at higher flow rates, while the j values in the cylindrical cell were independent of flow rate.…”

“…Thus, no transmission correction factor need be applied when the reactor is infinite in length, or where there is no inlet/outlet system, since the internally reflected light ray will exactly compensate for the reflected light lost initially (Zafonte et al, 1977). An 'end correction' can be made for a finite tubular reactor, which is proportional to the area of the endcaps and inversely proportional to a function of photolysis cell length.…”

“…Orientation of the tube in the NorthSouth direction resulted in an estimated maximum shading of the cell of < 1% during ambient measurements, so the end correction was considered negligible. Dickerson and Stedman (1980) tested the validity of the calculations done by Zafonte et al (1977) by sliding one to three additional tubes over their photolysis tube, and measuring the j value; within the precision of their experiment (±5%), the additional tubes had no effect on the measured j value. Jackson et al (1975) further verified the validity of the calculations by rotating the cell in a range of orientations and observing <5% change in signal.…”

Measurement of the photodissociation coefficient of NO2 in the atmosphere: I. Method and surface measurements

“…The effect of reflection in the double quartz cylinder was determined by ray-tracing, using an approach similar to that used by Zafonte et al (1977) for a single wall, infInitely long, cylinder. For an infInitely long, non-absorbing, double-walled cell the reflection losses are also compensated by multiple internal reflections for all angles of incidence (Madronich, 1982).…”

“…with those of Zafonte et al (1977). The correlation curve given by Harvey et al (1977) is shown in Figure 8 for comparison.…”