John A. Lind

An intercomparison of formaldehyde measurement techniques at ambient concentration

Abstract A study was conducted to evaluate five techniques for determining ambient formaldehyde concentrations. One technique used a spectroscopic determination, and the other four techniques used derivatization followed by fluorometric analysis or high-performance liquid chromatography with detection by u.v. absorption. Formaldehyde was generated by two techniques. In the first technique, zero air was bubbled through a solution of aqueous formaldehyde to produce gas-phase formaldehyde. Various compounds serving as possible interferences were added singly or in combination to these air mixtures. In the second technique, formaldehyde was generated as a product from controlled irradiations of hydrocarbons and nitrogen oxides in a smog chamber operated in a dynamic mode. The study was conducted as a blind intercomparison with no knowledge by the participants of the HCHO concentrations or the interferences added. The data from each of the techniques were compared against mean values in each sampling period. For formaldehyde in zero air, average deviations for each of the techniques ranged between 15 and 30%. At a formaldehyde concentration of 10 ppb, each technique showed no evidence for interferences by O3 (190 ppbv), NO2 (300 ppbv), SO2 (20 ppbv), and H2O2 (7 ppbv). The agreement for formaldehyde concentrations measured for the photochemical mixtures was similar to that of the mixtures in zero air. Ambient measurements were also performed on three evenings and for one 36-h period. Ambient formaldehyde concentrations ranged from 1 to 10 ppbv. Ambient H2O2 measurements were also performed. A strong correlation in the diurnal concentration profile for formaldehyde and H2O2 was observed over the 36-h period.

Comparison of techniques for measurement of ambient levels of hydrogen peroxide

A study measured hydrogen peroxide (H/sub 2/O/sub 2/) from three sources: (1) zero air in the presence and absence of common interferences; (2) steady-state irradiations of hydrocarbon/NOX mixtures; and (3) ambient air. The techniques employed for measuring H/sub 2/O/sub 2/ included infrared absorption from a diode laser, fluorescence from an enzymatically produced complex, and chemiluminescence from reaction with luminol. Four systems, each of which utilized one of the above techniques, were compared with respect to sensitivity, selectivity, and dynamic range in measuring H/sub 2/O/sub 2/ concentrations ranging from 0.062 to 128 ppbv. There was no indication of interferences for an H/sub 2/O/sub 2/ level of 6 ppbv except in the luminol technique, where a negative interference was caused by SO/sub 2/. Agreement among techniques was much worse for measurement of H/sub 2/O/sub 2/ produced in the photochemical mixtures. Significant concentrations of organic peroxide were measured by the enzymatic technique. During ambient monitoring, the techniques employed showed quantitative agreement.

An airborne study of air quality around the Hong Kong Territory

An airborne study of air quality was made around the Hong Kong Territory during October and November of 1994. The air quality measurements included NO, NO y , O 3 , CO, SO 2 , condensation nuclei, black carbon, aerosol light scattering, and aerosol particle size and number. Complex wind patterns are present, mixing the emissions from Hong Kong with aged pollution transported into the region from the Peoples Republic of China. This leads to poor air quality on the west and north sides of the Hong Kong Territory. CO mixing ratios were 200-800 parts per billion by volume (ppbv), and black carbon was present in the range of 5-7 μg/m 3 . Ozone mixing ratios of 100-120 ppbv were typical. The CO/NO y ratio in the heavily polluted region was 10, similar to the CO/NO y emission ratio for pollution emitted from the Peoples Republic of China immediately upwind of Hong Kong.

Measurements of NO x and PAN and estimates of O3 production over the seasons during Mauna Loa Observatory Photochemistry Experiment 2

Measurements of peroxyacetyl nitrate (PAN) and NOx and a variety of other constituents were made over approximately 1-month-long intensives in the autumn of 1991 and the winter, spring, and summer of 1992 during the second Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2). PAN and NOx in the free troposphere had maximum abundances in spring in concert with the well-known maximum in O3. The ratio of the spring to summer averages was a factor of 4.1 for PAN, a factor of 1.6 for O3, and only a factor of 1.4 for NOx. During most intensives, variations over periods of a few days to a week were often larger than the average seasonal amplitude. In free tropospheric air masses local to Hawaii, average PAN/NOx ratios were a maximum in winter through spring but in the range of 0.25–0.86 in all intensives. PAN decomposition is unlikely to be the major net source of NOx in local air masses in summer and fall. The low HNO3/NOx ratios determined during MLOPEX 1 were confirmed during MLOPEX 2. Intensive average ratios of 1.6–3.8 over the year are lower than some model predictions. Both the low ratio and the magnitude of NOx imply a shortcoming in our understanding of the transformations and sources of NOy constituents in the central Pacific, The 3- to 4-km altitude region near Hawaii was a net importer of O3, on average, over the year. The average net rate of production of O3 in free tropospheric air was near zero in winter, −0.4 to −0.8 ppbv/d in spring, −1.4 ppbv/d in summer, and −0.6 ppbv/d in autumn. Thus the spring maximum in O3 is not due to local photochemistry. We believe, as has been concluded from the long-term measurements of long-lived constituents by the Climate Monitoring and Diagnostics Laboratory, that the variation of ozone precursors over the year and on shorter timescales of a few days to a week is controlled predominantly by changes in long-range transport: more frequent sampling of higher-latitude and higher-altitude air masses in winter and spring versus more frequent sampling of well-aged air from lower altitudes and latitudes in summer and autumn.

Measurements of Hydrogen Peroxide and Formaldehyde in Glendora, California

Gas-phase hydrogen peroxide (H/sub 2/O/sub 2/) and formaldehyde (HCHO) were measured in Glendora, California from August 14-21, 1986. These measurements were part of the Carbonaceous Species Methods Comparison Study sponsored by the California Air Resources Board. Both of these species were measured using enzymatic techniques: H/sub 2/O/sub 2/ by the peroxidase catalyzed dimerization of p-hydroxyphenylacetic acid and formaldehyde by the formaldehyde dehydrogenase catalyzed reduction of NAD/sup +/ to NADH. Both H/sub 2/O/sub 2/ and HCHO showed a strong diurnal variation with the highest concentrations measured during the period of maximum photochemical activity. H/sub 2/O/sub 2/ concentrations ranged less than 0.1 ppbv at night to a maximum of 3 ppbv for the hourly average on one day. The HCHO concentrations ranged from a low of 5 ppbv at night to a maximum of 20 ppbv during the day.

Spring measurements of tropospheric bromine at Barrow, Alaska

The partitioning of bromine in the lower troposphere between particulate, inorganic gaseous, and organic gaseous phases was measured during the arctic spring. Rapid photochemical production of particulate Br[sup [minus]] from organic gaseous Br was indicated by (1) an inverse correlation between particulate bromide and organic gaseous bromine (r[sup 2] = [minus]0.67), (2) a diurnal cycle in the ratio of these two phases, and (3) a diurnal cycle in the ratio of organic gaseous Br to Cl. Organic gaseous Br and Cl were correlated (r[sup 2] = 0.67) indicating a common, possibly marine, source. 9 refs., 6 figs.

A Comparison of Aircraft and Ground-Based Measurements at Mauna Loa Observatory, Hawaii, During GTE PEM-West and MLOPEX 2

During October 19-20, 1991, one flight of the NASA Global Tropospheric Experiment (GTE) Pacific Exploratory Mission (PEM-West A) mission was conducted near Hawaii as an intercomparison with ground-based measurements of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2) and the NOAA Climate Modeling and Diagnostics Laboratory (CMDL). Ozone, reactive nitrogen species, peroxides, hydrocarbons, and halogenated hydrocarbons were measured by investigators aboard the DC-8 aircraft and at the ground site. Lidar cross sections of ozone revealed a complex air mass structure near the island of Hawaii which was evidenced by large variation in some trace gas mixing ratios. This variation limited the time and spatial scales for direct measurement intercomparisons. Where differences occurred between measurements in the same air masses, the intercomparison suggested that biases for some trace gases was due to different calibration scales or, in some cases, instrumental or sampling biases. Relatively large uncertainties were associated with those trace gases present in the low parts per trillion by volume range. Trace gas correlations were used to expand the scope of the intercomparison to identify consistent trends between the different data sets.

Summertime diurnal variations of atmospheric peroxides and formaldehyde in Sweden

Atmospheric peroxides and formaldehyde were measured at two sites in Sweden; inside a Scots pine stand (Jädraås) and on top of Mt. Åreskutan (1250 msl). Peroxide levels at Jädraås were highest during the day and lowest during the night. Mid-day concentrations of H2O2 varied between 0.05 and 2 ppbv. Isentropic trajectories together with local O3 measurements indicated the importance of long range transport on surface H2O2 lévels. Large diurnal variations and vertical profiles showed the importance of turbulent mixing processes and dry deposition. A comparison of H2O2 and O3 diurnal variations indicated a more rapid dry deposition of H2O2 to the forest. It would appear that terpenes emitted from the forest play a minor role in controlling the H2O2 levels. Formaldehyde at Jädraås had a different diurnal variation than peroxides; highest levels were observed in the early evening indicating chemical production of CH2O. Diurnal variations of peroxides on Mt Åreskutan were opposite to those at Jädraås, highest concentrations were observed during the night. This result is to be expected if during the day air from inside the valley, with lower peroxide levels relative to the free troposphere, rises to the mountain top. In the evening, subsidence brings free tropospheric air with higher peroxides levels to the mountain.

Chemical amplifier for peroxy radical measurements based on luminol chemiluminescence

We report measurements of atmospheric peroxy radicals which were made at two rural sites in the eastern United States using the technique of chemical amplification followed by luminol chemiluminescence detection. Several improvements which have been made to the instrumental systems since earlier reports are discussed. Also reported is a new field calibration procedure which allows a critical evaluation of the instrumental stability and provides directions for design changes to improve its performance.