Heinz W. Biermann

Measurement of nitrate radical concentrations in continental air

Nighttime profiles of the atmospheric concentrations of the nitrate radical (NO/sub 3/), NO/sub 2/, and O/sub 3/ have been obtained by using a mobile differential ultraviolet/visible absorption spectrometer over path lengths from 3 to 17 km. Measurements were carried out at four semiarid/desert sites in the southern California desert (Death Valley, Edwards Air Force Base, Phelan, and Whitewater), and nitrate radicals were observed at all four locations at typical concentrations of approx. 10-100 parts per trillion. A decrease in the calculated NO/sub 3/ lifetime with increasing relative humidity (RH) was observed with lifetimes up to approx. 60 min for less than or equal to50% RH, but less than or equal to10 min for greater than or equal to50% RH. This suggests the involvement of water in the loss process for NO/sub 3/, either in the gas phase or in the aqueous state at the ground or on aerosol surfaces. These experimental field data support our earlier hypothesis that this loss process of NO/sub 3/ may constitute both a major sink for atmospheric NO/sub x/ and a significant formation route for nitric acid, a key component of acid rain and fog.

The nitric acid shootout: field comparison of measurement methods

Eighteen instruments for measuring atmospheric concentrations of nitric acid were compared in an eight day field study at Pomona College, situated in the eastern portion of the Los Angeles Basin, in September 1985. The study design included collocated and separated duplicate samplers, and the analysis by each laboratory of a set of quality assurance filters, so that the experimental variability could be distinguished from differences due to measurement methods. For all sampling periods, the values for nitric acid concentrations reported by the different instruments vary by as much as a factor of four. The differences among measurement techniques increase with nitric acid loading, corresponding to a coefficient of variation of 40%. In contrast, samplers of the same design operated by the same group show variability of 11–27 %. Overall, the highest reported concentrations are observed with the filter packs and lower concentrations are observed by the annular denuders and tunable diode laser absorption spectrometers. When the nitric acid concentrations are high enough to be detected by the FTIR, the FTIR values are close to those obtained by the denuder difference method and to the mean value from the other sampler groups. In the absence of a reference standard for the entire study, measurement methods are compared to the average of four denuder difference method samplers (DDM). Filter pack samplers are higher than the DDM for both daytime and night-time sampling. Two different filter packs using Teflon® prefilters are higher than the DDM by factors of 1.25 and 1.4. The results from the three annular denuders do not agree; the ratios of means to the DDM value are 1.0,0.8 and 0.6. For the transition flow reactor method and for two dichotomous samplers operated as denuder difference samplers, the ratio of means to the DDM are 1.09 and 0.93, respectively. The tunable diode laser absorption spectrometers gave lower daytime and higher night-time readings compared to the DDM, especially during the last three days of the study. Averaged over the entire measurement period, the daytime ratio of TDLAS to DDM is 0.8 and the night-time ratio is 1.7.

Spectroscopic identification and measurement of gaseous nitrous acid in dilute auto exhaust

We report here the direct spectroscopic detection of gaseous nitrous acid (HONO) in exhaust emissions from certain light duty motor vehicles (LDMV). Co-pollutants such as nitrogen dioxide (NO2), formaldehyde (HCHO), benzaldehyde (C6H5CHO) and sulfur dioxide (SO2) were also readily determined. Nitric oxide (NO) was measured too, but with reduced accuracy. To avoid possible artifactual formation of HONO on the surfaces of conventional dilution and sampling systems (e.g. Federal and California constant volume sampling systems), an instrument was developed consisting of a multiple reflection cell without walls coupled to a u.v. differential optical absorption spectrometer (DOAS), the entire system being placed in the open air ~ 2 m from the tailpipe of the LDMV. At an optical path of 31.2 m, detection limits (in parts per 109, ppb) were: HONO-12; HCHO-78; C6H5CHO-13; NO2-57; and SO2-11. With this instrument, HONO levels observed in diluted exhaust ranged from nondetectable (< 12 ppb) for a 1982 California car with an effective 3-way catalyst (and associated low NOx emissions), to ~ 300 ppb for a heavily used 1974 station wagon having high NOx emissions and run on leaded gasoline. While the number of LDMV tested was too small for statistical treatment, our results show that the older portion of the total LDMV population (i.e. without current emission control devices) may be a significant primary source of gaseous HONO, a key precursor to photochemical air pollution and an inhalable nitrite.

Simultaneous absolute measurements of gaseous nitrogen species in urban ambient air by long pathlength infrared and ultraviolet-visible spectroscopy

Abstract Two new long pathlength spectrometers, utilizing 25-m basepath multiple reflection optical systems, were employed for the first time during an intercomparison of measurement methods for atmospheric nitrogenous species held at Claremont, CA, 11–19 September 1985. Measurement of nitrogenous species using these closed optical path systems, as opposed to single pass systems extending several kilometers, permit the resulting in situ absolute spectroscopic data to serve as benchmark values for point monitors employing denuders or filter packs. The FT-IR spectrometer was operated at a total pathlength of 1150 m and spectral resolution of 0.125 cm −1 , with corresponding detection sensitivities of 160 nmolem −3 for HNO 3 and 60 nmole m −3 for NH 3 (4 and 1.5 ppb, respectively). Concurrent measurements of HONO, NO 2 and NO 3 radicals were conducted with the differential optical absorption spectrometer operated at 800 m total pathlength with detection limits of 24, 160 and 0.8 nmole m −3 (0.6, 4 and 0.02 ppb) for HONO, NO 2 , and NO 3 radicals, respectively.

Identification and measurement of nitrous acid in an indoor environment

Abstract We report here direct observation by differential optical absorption spectroscopy (DOAS) of the formation of ppb levels of gaseous nitrous acid (MONO) from the reaction of ppm levels of nitrogen dioxide (NO 2 ) with water vapor, in an indoor environment. The rate of formation of HONO displayed first order kinetics with respect to NO 2 with a rate of (0.25 ±0.04) ppb min −1 per ppm of NO 2 present. Assuming a lifetime of l h with respect to both physical and chemical removal processes for HONO, this leads to an estimated steady state concentration of ~ 15 ppb of HONO per ppm of NO 2 present. This relatively high level of HONO associated with NO 2 -air mixtures raises new questions concerning the health implications of elevated NO 2 concentrations in indoor environments e.g. HONO is a respirable nitrite known to convert secondary amines in vitro to carcinogenic nitrosamines.

Comparison of atmospheric nitrous acid measurements by annular denuder and differential optical absorption systems

As part of the Southern California Air Quality Study (SCAQS), nitrous acid (HONO) measurements were made at Long Beach, CA during the period 11 November–12 December 1987, using two distinctly different techniqes. One of these, the annular denuder method (ADM), used two denuders in tandem, coated with an alkaline medium to obtain 4- or 6-h integrated measurements. A small FEP Tefloncoated glass cyclone preceded the denuders to exclude coarse particles while minimizing loss or artifactual formation of HONO. Nitrite recoveries from the rear denuder were used to correct for sampling artifacts. In the second method, 15 min average HONO concentrations were measured with a differential optical absorption spectrometer (DOAS) coupled to a 25 m basepath, open multiple reflection system operated at a total optical path of 800 m. Period-averaged HONO concentrations from the two techniques were highly correlated (r = 0.94), with DOAS results averaging about 10% higher. However, ADM results were biased high at low HONO concentrations. HONO and NO concentrations showed a significant, positive correlation (r = 0.8), consistent with a common emission source (e.g. auto exhaust) for the two pollutants.

Time-resolved identification and measurement of indoor air pollutants by spectroscopic techniques: Gaseous nitrous acid, methanol, formaldehyde and formic acid

The results are reported of a quantitative study of HONO, NO{sub 2} and H{sub 2}CO levels in the mobile office/home using a new residential, gas-fired kitchen stove and kerosene- or propane-fueled space heaters. We also report results from the use of an FT-IR spectrometer which allowed us to search not only for nitric acid in the polluted indoor air containing HONO and NO{sub 2}, but also for organics. We report for the first time the unambiguous, simultaneous identification and measurement of indoor gaseous HCOOH and CH{sub 3}OH, apparently from the building materials which, like the HONO, are at levels exceeding those typically found in outdoor urban environments.