NO3 has been measured in slightly polluted Colorado mountain air up to a few hundred ppt. There is clear evidence that it is removed by scavenging reactions in less than one hour. The identity of the scavenger is not yet established in mountain air, nor is it yet known whether the reaction removes odd nitrogen from the troposphere. In urban air the scavenging occurs in less than a few hundred seconds and may in part be due to the reaction of NO3 with NO.

The determination of the concentration of OH in the Earth's troposphere is of fundamental importance to an understanding of the chemistry of the lower atmosphere. Although many experiments to measure OH concentration have been performed in recent years, very few operate at sensitivities necesssary to measure the extremely low amount of OH in the clean troposphere (0.1-0.2 parts per trillion by volume at summertime local noon). This paper describes an informal intercomparison campaign held at Fritz Peak, Colorado, in summer 1991 to intercompare the OH concentrations determined from a spectroscopic instrument and an in situ chemical conversion instrument, both with sensitivities at or below 5 x 105 molecules cm -3. Ancillary measurements including those of 0 3, CO, NO, NO 2, NO., H20, SO 2, aerosols, solar flux, and meteorological parameters were also performed to test photochemical theories of OH formation. These measurements also provided a means for comparing air masses at the long path and in situ sites. The intercomparison was very successful with measured values of OH concentration in agreement within one standard error much of the time. OH concentrations were typically low, rarely above 4 x 106 cm -3, with only slow growth during the morning hours, indicating the possible presence of scavenger species. Model results suggest higher than measured OH concentrations or the presence of scavenger species. Logan et al. [1981] have placed OH chemistry in the framework of the global troposphere. Tropospheric OH is formed (mainly) by the reactions EISELE ET AL.' TROPOSPHERIC OH AND TRACE GAS MEASUREMENTS 18,607 Boulder/Gilpin County, Colorado Caribou Mine ? er ,,,17 km •" '•'"'•':• N e d e r I a n d Eldore North o linsvi e contour intsrval-122 meters Fritz Peak Observatory 2,676m Figure 2. Topographic map of the area, including Fritz Peak Observatory and Caribou with local (very small) towns shown. Wind is typically from the west. measurement of atmospheric absorption of individual rotational lines in the ultraviolet electronic OH bands near 308 nm; (5) a two-channel arra• detector system with signalto-noise ratio greater than 10•* per integration that allows simultaneous observation of both laser and atmospheric absorbed laser light at all wavelengths in a spectral interval sufficient to include measurement of several OH rotational Caribou Mlnl• / Ob•,•tmO, , ,o.• / -I 2.50 m Retro Reflector Array Laser • • OH Path Geometry Cross Section As Seen From East concentration of H2SO 4 and methane sulfonic acid and estimates of H2SO 4 production and loss in the atmosphere, J. Geophys. Res., 98, 9001-9010, 1993. Evaluation of a catalytic reduction technique for the measurement of total reactive odd-nitrogen, NOy, in the atmosphere, J. Atmos. Chern., 3, 435-468, 1985. nitrogen species in the troposphere: Measurements of NO, NO 2, HNO 3, particulate nitrate, peroxyacetyl nitrate (PAN), 03, and total reactive odd nitrogen (NO) at Niwot Ridge, Colorado, J. Geophys. Res., 91, 9781-9793, 1986. Impact of natural hydrocarbons and hy...

No abstract

Satellite electron temperature and density data are used to calculate the structure of several stable auroral red arcs (SAR arcs) according to the thermal conduction model of the arc. The calculated λ6300 emission rates are compared with ground‐based photometric observations taken at the same time and in the vicinity of the satellite crossings of the arcs. The SAR arcs analyzed include a range of λ6300 intensities, geographical locations, and times during the associated geomagnetic storm. In addition, satellite data were obtained at different altitudes over and within the SAR‐arc region. Enhanced electron temperatures within or on the equatorward edge of an electron‐density depression are common features of all the SAR arcs examined. There is general agreement between the calculated and observed X6300 emission features for SAR arcs observed during the geomagnetic storm periods of October 29 to November 2, 1968, May 14–15, 1969, and March 8–9, 1970. For these SAR arcs, thermal conduction from the magnetosphere alone is sufficient to excite the λ6300 emission to its observed intensity.

Abstract. The determination of the concentration of hydroxyl (OH) in the Earthat or below 1 x 106 molecules cm -3. In addition to the OH measurements, a nearly complete suite of trace gas species that affect the OH concentration were measured simultaneously, using both in situ and/or long-path techniques, to provide the information necessary to understand the OH variation and concentration differences observed. Measurements of OH, NO 2, CH20, SO2, H20, and 0 3 were made using long-path spectroscopic absorption of white light or laser light and OH, NO, NO 2, NOy, 03, CO, SO 2, CH20, j(O3) , j(NO2) , RO2/HO2, HO2, H20 , SO2, PAN, PPN, HNO 3, and aerosols (size and composition) and ozone and nitrogen dioxide j-values were measured using in situ instruments. Meteorological parameters at each end of the long path and at the Idaho Hill in situ site were also measured. The comparison of the long-path and in situ species from this set of complementary measurements provides an effective way of interpreting air masses over the long path with those at the in situ site; this is a critical issue since the long-path spectroscopic OH determinations provide a nonchemical and well-calibrated measurement of OH which must be compared in a meaningful manner with the in situ determinations. Over the period of the TOHPE experiment, OH concentrations were typically low during periods of clean and clear airflow, averaging about 4 x 106 molecules cm -3 at noon. In contrast, during the well-defined pollution episodes which occurred during the campaign, OH concentrations rose as high as 15 x 106 molecules cm -3.