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.
Evaluation of a high-purity and high-stability continuous generation system for nitrous Acid.
A flow-type system for the generation of nitrous acid in the mass flow rate range of 3.5-400 nmol/min is described. The system based on the reaction between gaseous hydrochloric acid, generated by means of a low-pressure permeation device, and solid sodium nitrite allows the continuous production of highly pure nitrous acid (purity >99.5%) and thus the generation of standard atmosphere in a very wide range of nitrous acid mixing ratio (5-20000 ppb). The system is of easy construction and exhibits a very high reproducibility and excellent long-term output stability. These features allow us to obtain any desired value of nitrous acid mass flow rate by simply tuning the temperature and flow rate values. As a consequence of the high purity of the generated compound, it was possible to obtain a clear absorption spectrum of nitrous acid without performing any correction for NO 2 interference.
Assessment of Ground Regeneration around Borehole Heat Exchangers between Heating Seasons in Cold Climates: A Case Study in Bialystok (NE, Poland)
Based on the experimental studies, the process of ground regeneration around the borehole loaded with brine-water heat pumps working exclusively for heating purposes in the period of four consecutive heating seasons in a cold climate was presented. The research was conducted in north-eastern Poland. The aim of the work is to verify the phenomenon of thermal ground regeneration in the period between heating seasons on the basis of the recorded data and to check whether the ground is able to regenerate itself and at what rate. It was noticed that the ground does not fully regenerate, especially during heating seasons with lower temperatures. In the analyzed period, from 22 September 2016 to 12 October 2020, the ground probably cooled irreversibly by 1.5 °C. In order to illustrate and evaluate the speed of changes in the ground, the one’s profile with an undisturbed temperature field was presented for each month of the year. The presented results can be a very important source of information for the analysis of geothermal conditions occurring in the ground. They can be used to verify mathematical models and conduct long-term simulations that allow us to see the complexity of the processes taking place in the ground.