EVALUATION OF NOy AND NITRIC ACID MEASUREMENT METHODS AND COLLECTION OF AMBIENT DATA
California has an ambient air quality standard for nitrogen dioxide (NO2), and oxides of nitrogen are also critical participants in atmospheric photochemistry to form ozone. Ambient air quality monitoring networks use chemiluminescent analyzers that alternately measure NO and all nitrogenous species that are converted to NO by a heated catalyst. The difference is defined as NO2. In the atmosphere these nitrogenous species (NOy) consist of, in addition to NO and NO2, nitrogenous acids (nitric and nitrous), ammonia (NH3), and organic nitrates. Dual converter NOx analyzers were used during SCOS97-NARSTO to measure NOy and nitric acid. These instruments were refurbished by replacing or reactivating their reduction converters and thoroughly evaluating their efficiency to convert nitrogen-containing species. These instruments are equipped with dual converters with one channel fitted with a NaCl-coated fabric denuder to selectively remove nitric acid (NOy*). Since the instrument automatically cycles between the two channels, the difference is a measure of nitric acid. A pair of collocated analyzers was set up at the CE-CERT laboratory in Riverside and a single analyzer was installed in Azusa at the monitoring site operated by the South Coast Air Quality Management District (SCAQMD). Data collection started April and October 2000, respectively, for the Riverside and Azusa measurement sites. Data were compiled and validated until April 2001. NOy values at Riverside ranged up to 300 ppb, and values at Azusa reached up to 500 ppb. The Azusa NOy and NOx reported by the SCAQMD compared quite closely. Since it was not possible to have both analyzers sample the same span gas, the significance of differences between the two approaches could not be evaluated. The diurnal pattern of nitric acid was observable nearly every day during the smog season. The concentrations at Riverside ranged up to 6 ppb in the summer. Despite the measurement period at Azusa not including the summer smog season, nitric acid concentrations as high as 8 ppb were observed. A thermoevolution denuder (TED) to measure nitric acid was evaluated under laboratory conditions. This device uses a special ceramic fabric denuder coated with sodium chloride to selectively remove nitric acid. Since this fabric strongly adsorbs microwave radiation at the same wavelength as that for cooking, the fabric can be heated rapidly and controllably to high iv temperatures using a standard microwave oven. This heating will decompose the collected sodium nitrate to NOx. While this design allowed the denuder to adsorb nitric acid, the amount recovered was low and variable. We found that the denuder was not evenly heated, and the amount recovered when drops of dilute nitric acid were placed on the denuder depended on the location on the denuder that was used. It was likely that the microwave oven, which was a consumer product, was not designed to produce a uniform microwave field. We concluded that additional research was needed before the system was ready to evaluate with other methods of measuring nitric acid. This report included the initial year of NOy and nitric acid data. We continued to maintain the NOy analyzers and added NO2/PAN gas chromatographs at both sites. These chromatographs separate NO2 and quantify the amount using luminol detection. This selective method of measuring NO2 will be used to quantify the amount of NO2 contained in the NOy. Under additional funding these instruments will be maintained until October 2002. The results from this period will be the subject of a final report for the second period of funding.
Nitric acid measurement methods: An intercomparison
Abstract An interlaboratory comparison of methods to measure gaseous nitric acid is described. Field experiments were conducted in Claremont, CA in late August and early September of 1979. Ten nitric acid measurement methods were compared during the 8 day field experiment. Six different research groups participated in the nitric acid measurements. The methods compared include 2 which employed chemiluminescence principles, 1 infrared, 2 diffusion denuder and 5 filtration techniques. The 8 study days were divided into 32 sampling intervals of 3, 6 and 12 h. Based on the median of the 10 methods, the nitric acid concentration ranged from 1.85 to 37.05μ gm −3 . The nitric acid concentration was highly correlated with other photochemical pollutants such as O 3 and PAN, and all three were strongly correlated with temperature and solar intensity. On the average, gaseous nitric acid and paniculate nitrate contributed equally to the total inorganic nitrate burden at the site. Of the 10 methods investigated, 5 exhibited excellent agreement with the median nitric acid concentration, 2 yielded slopes significantly exceeding 1.0 and 3 suffered from problems which resulted in relatively poor agreement with nitric acid concentration. A great many chemical and meteorological variables were measured during the study, and the effects of these ancillary variables on the nitric acid measurement methods are discussed.
Implementation of Tourism Satellite Account: Assessing the Contribution of Tourism to the Croatian Economy
Compiling the indicators of tourism consumption and the output of tourism industries, Tourism Satellite Account (TSA) provides a framework for internationally harmonized measurements of direct macroeconomic contribution of tourism. Ivandic and Marusic provide a detailed methodological approach for the transfer of TSA theoretical concepts to the assessment of tourism economic contribution on the case of the Croatia. Giving that the TSA compilation is still characterized by a surprisingly wide range of ‘styles’ used, the chapter contributes to a better understanding of the issues related to measurement of direct tourism impacts. It also gives a set of baseline criteria for resource allocation within tourism policy and the further evaluation of its effectiveness.