Richard A. Wadden

Characterization of potential indoor sources of ozone

Ozone emission factors were developed for domestic electrostatic air cleaners and photocopying machines. The air cleaners had emission rates from 0-546 microgram/min. These rates will ordinarily not produce air concentrations which are greater than 60 microgram/m3 (0.030 ppm) above background. The emission rate for photocopying machines varied from 48-158 microgram/copy. In small, poorly ventilated rooms these emission rates were sufficient to produce incremental steady state ozone concentrations up to 396 microgram/m3 (0.202 ppm). Recent copying machine maintenance was found to reduce ozone production to less than the detectable level, 4 microgram/m3 (0.002 ppm).

Comparison of three methods of particulate measurement in Chicago air

Abstract Simultaneous measurements of suspended particulate concentrations were taken in Chicago over an 8-month period with an integrating nephelometer, a 6-stage fractionating sampler, and a Hi-Vol air sampler. The correlation coefficient ( r ) between light scattering coefficient, b scat , and the Hi-Vol measurements was 0.75. The light scattering coefficient was found to be highly correlated with the impactor stages which had cut-off diameters of 0.38 μm ( r = 0.79) and 0.84 μm ( r = 0.89). These associations were independent of relative humidity. In contrast, correlations between b scat and all other size fractions, and with TSP, were greatly affected by relative humidity. Relatively strong relationships were also found between NO 2 , O 3 and b scat which support the contention that nephelometer measurements are a reflection of photochemical activity.

A model of a growing, coagulating aerosol

A continuously reinforced aerosol, undergoing change by particle growth and coagulation, and particle removal at some selected large size, is described by a number balance equation. For the steady state condition, the number balance equation was solved numerically for the distribution of particle concentrations as a continuous function of particle volume. The particle growth rate, Φ(v), was based on rate data describing the Mn2+, Fe3+, and non-catalyzed aqueous phase conversion of SO2(g) to H2SO4(aq). The catalyst and the H2SO4 were assumed to be contained in drops, which grew with acid production, due to the accretion of water vapor. The number balance equation without growth was also solved. Calculations on the Mn2+ catalyzed systems resulted in distributions which reflected detectable effects of both growth and coagulation. For sufficiently large values of Φ(v) (> 10−10 μ3min−1), corresponding to SO2(g) concentrations of 0.1–10 ppm. the resulting distributions were found to display two regions, one dominated by growth and the other by coagulation. The particle size distribution in the growth region (small v) is similar in shape to 1/Φ(v), while in the coagulation region (large v) the particle distribution is a straight line on a log-log plot. The shape of the input distribution did not have an effect on the shape of the calculated distribution. The neutralizing effects of NH3(g) on the Mn2+ catalyzed aqueous phase reaction were also checked and the resulting distribution has a shape similar to those at high SO2(g) concentrations (10 ppm). The Fe3+ catalyzed and non-catalyzed systems (Φ(v) ≦ 10−12μ3 min−1) displayed only a coagulation region. At large values of v, calculated distributions for all systems displayed a power law relationship between particle concentration and volume with a slope of − 1.3 to −1.5. The H2SO4 or (NH4)2SO4 composition of the particles was found not to be a function of size.

Analysis of indoor concentrations of carbon monoxide and ozone in an urban hospital

Carbon monoxide (CO) and ozone (O3) were monitored in an office and two intensive care units of an urban hospital for 1 year. Annual average indoor CO concentrations averaged 0.2 to 1.3 ppm higher than outdoor concentrations (significant at P < 0.05), with indoor levels of 2.2 to 3.1 ppm. These differences were the result of indoor sources, probably smoking. Annual average indoor O3 concentrations averaged 0.005 ppm less than those outdoors (significant at P < 0.05), with a range of indoor means from 0.007 to 0.013 ppm. Indoor concentrations of both pollutants were modeled by performing a mass balance for each area. The predicted and observed annual average indoor concentrations were within 0.3 ppm for CO for areas with identified sources and 0.003 ppm for O3. Because of a relatively unsophisticated characterization of indoor sources, comparisons of hourly predictions were less accurate, although correlation coefficients between observed and predicted were as high as 0.71 for CO and 0.91 for O3.

Modification and operation of a size selective atmospheric particulate sampler

Statistically significant differences were observed between total suspended particulate measurements in Chicago collected concurrently with a HiVol and a six-stage fractionating sampler. The size-selective sampler was modified and atmospheric suspended particulate data were collected for 1 year using the modified sampler. Based on these data it appears that: 1. (1) the agreement between HiVol and the size selective sampler is seasonally dependent; 2. (2) comparison of HiVol and size-selective sampler data, before and after modification, indicates that the modifications were partially successful but that a significant difference remained between the two collection devices; 3. (3) a least squares fit of total particulate concentration for the modified sampler vs the HiVol gave a relationship essentially the same as one reported by other observers for a similar type of sampler; 4. (4) correlation coefficients between each fraction of the modified size-selection sampler and the HiVol were > 0.74 for the largest and smallest fractions (d > 2.76 μm; d < 0.39 μm) and < 0.31 for the intermediate fractions (0.39 μan < d < 2.76μm): and 5. (5) the annual average size distribution shows a lower mass median diameter than has been reported for 1970 and 1972 for Chicago, which may reflect the implementation of stationary source control regulations.

Specification of Source Characteristics for Ozone Prediction in a Complex Airshed

Photochemical O3 is formed in the atmosphere as a result of complex non-liner interaction of meteorology, emission distribution and chemical reactions. To investigate the urban O3 reduction strategy a three-dimensional grid model including meteorology, chemistry and emissions based on the real conditions should be needed.