Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991) / Chapter Skim
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7 Techniques For Measurement of Reactive Nitrogen Oxides, Volatile Organic Compunds, and Oxidants
7 Techniques For Measurement of Reactive Nitrogen Oxides, Volatile Organic Compunds, and Oxidants
Pages 187-210
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From page 187... ...
, and oxidizing radicals, the concentration of these compounds also must be measured to test present understanding of atmospheric oxidation mechanisms. If measurements are to be meaningful, reliable instruments and techniques are necessary.
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From page 188... ...
MEASUREMENT TECHNIQUES FOR OXIDES OF NITROGEN AND THEIR OXIDATION PRODUCTS The reactive oxides of nitrogen in the atmosphere are largely nitric oxide (NO) and nitrogen dioxide (NO2)
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From page 189... ...
, chemiluminescence instruments and a laser-induced fluorescence instrument measured ambient concentrations simultaneously at a rural site and from an aircraft. The data agreed within 30% in all of these chemically different environments and over concentrations of NO spanning a range of 0.005 to 0.2 parts per billion (ppb)
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From page 190... ...
, and luminol chemiluminescence. The LIF and TDLAS techniques provide specific spectroscopic methods to measure NO2; the luminol technique provides a sensitive, portable method with low power requirements.
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From page 191... ...
Over an 8-day period at a site with urban and suburban characteristics, six methods were used to make simultaneous measurements: filter pack, denuder difference, annular denuder, transition flow reactor, tunablediode laser, and Fourier transform infrared spectrometer. The reported concentrations of HNO3 varied by more than a factor of 2.
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From page 192... ...
The filter packs exhibited a positive bias (systematically higher than average HNO3 concentrations) that increased as the sampling time average increased, indicating an artifact due to ammonium nitrate particle evaporation to release HNO3 (and ammonia)
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From page 193... ...
However, in field measurements made at a rural site, the nylon filter yielded HNO3 mixing ratios 70% larger than those measured simultaneously by mist-chamber techniqes. Subsequent tests revealed a small positive interference for ozone on the nylon filter, but this interference could not account for the large discrepancy noted above.
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From page 194... ...
MEASUREMENT TECHNIQUES FOR CARBON MONOXIDE AND VOLATILE ORGANIC COMPOUNDS Unlike the NOX measurement techniques described above, which are adequate, the techniques for measuring VOCs and their oxidation products do not meet current needs. The analysis of VOCs is complicated by the extreme complexity of the mixtures that can be present in the atmosphere.
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From page 195... ...
Concentrations above this background can indicate air masses that have had recent anthropogenic pollution input. Given the relatively unreactive nature of the gas and its high concentrations, it is expected to be one of the more easily measured trace atmospheric species.
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From page 196... ...
Large amounts of compounds, particularly high-carbon-number compounds, can be retained by the trapping medium. In addition, reactions between the VOCs and oxidants, such as residual ozone that survives the collection procedures, may destroy some hydrocarbons and produce other compounds not originally in the sampled air.
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From page 197... ...
In this study, no large systematic errors were observed in synthetic air mixtures with and without added interferants such as NO2, SO2, 03, and H2O2, or, for the TDLAS, EF, and DNPH techniques, in ambient air where ambient concentrations of HCHO ranged from 1 to 10 ppb. Although reasonably low concentrations of HCHO were encountered during this comparison, no attempt was made to establish detection limits for these instruments.
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From page 198... ...
In GC-FID analysis of ambient air, artifact formation of carbonyl compounds can arise in the cryogenic collection of an air sample. Thus far there have been
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From page 199... ...
Not enough is known about their chemistry and atmospheric distribution to predict how their oxidation will influence ozone formation. There are many measurement techniques for collecting organic acids, but few tests have assessed their validity.
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From page 200... ...
and organic peroxy (RO2) free radicals have been made with two different techniques, peroxy radical chemical amplif~cation (PeRCA)
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From page 201... ...
Each has advantages for certain kinds of tropospheric ozone measurements. The absorption of UV light by the ozone molecule provides a reasonably straightforward and accurate means to measure ozone.
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From page 202... ...
For this reason chemiluminescence has been used to measure ozone fluxes that can be deduced from the correlation of ozone variation with atmospheric turbulence. Electrochemical sondes measure the electrical conductivity of an electrolytic solution and rely on the conversion of chemicals in the solution by ozone in the sampled air, which alters the conductivity of the solution.
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From page 203... ...
These three techniques had detection limits for the measurement of H2O2 of approximately 0.1 ppb. In the tests done in synthetic air containing irradiated mixtures of NMHC and NOX, the agreement among the techniques was not as good, suggesting the presence of some as-yet unidentified H2O2 interference.
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From page 204... ...
The development of measurement techniques to study multiphase chemistry in the troposphere, the validation of these techniques, and the application of these techniques to atmospheric measurements should be encouraged. LONG-TERM MONITORING AND INTENSIVE FIELD MEASUREMENT PROGRAMS The measurement techniques described here must be used in well-designed field studies to collect the data necessary to evaluate tropospheric ozone production.
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From page 205... ...
Intensive Field Studies Understanding of ozone production outside urban areas has been greatly advanced by several field studies designed to elucidate atmospheric photochemical processes (for example, Dennis et al., 1990~. The experience from these studies is that much more is learned from the simultaneous measurement of many photochemical processes and meteorological events than is possible from the separate measurement of each.
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From page 206... ...
Aerosol chemistry sampling included: mutagens, metals, organics, particulate matter, carbon, NO3-, SO4-, and polyaromatic hydrocarbons. Size resolved aerosol chemistry involved organic carbon, elemental carbon, and nighttime bromine and lead.
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From page 207... ...
The evolution of the planetary boundary layer, which controls much of the mixing in the lower troposphere, was monitored by balloon-launched radiosondes and by wind measurements by SODAR and boundary layer radar systems. Other integrated, intensive field studies now planned or under way include the San Joaquin Valley Air Quality Study (SJVAQS)
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From page 208... ...
, even at the low concentrations found in rural and remote air, have been developed recently, and methods that measure nitric oxide (NO) , nitrogen dioxide (NO2)
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From page 209... ...
As a result, it is not known whether the lack of success of ozone control efforts is the result of failure to achieve targeted reductions in ozone precursors or failure to set appropriate targets. Also, questions remain about the relative importance of anthropogenic and biogenic VOCs, the extent to which ozone production is VOC-limited or NOx-limited, and the role of VOC and NOX oxidation products in ozone formation.
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From page 210... ...
210 RETHINKING THE OZONE PROBLEM that could mask important trends. Only measurements made by skilled operators with reliable instruments can ensure that the science on which emission controls are based is correct and that the effectiveness of these controls is adequately assessed.
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