NO2 Mixing Ratios Research Articles

Metabolism of nitric oxide in soil and denitrifying bacteria

Production and consumption of NO was measured under anaerobic conditions in a slightly alkaline and an acidic soil as well as in pure cultures of denitrifying Pseudomonas aeruginosa, P. stutzeri, P. fluorescens, Paracoccus denitrificans, Azospirillum brasilense, and A. lipoferum. Growing bacterial cultures reduced nitrate and intermediately accumulated nitrite, NO, N2O, but not NO2. Addition of formaldehyde inhibited NO production and NO consumption. In the presence of acetylene NO was reduced to N2O. Net NO release rates in denitrifying bacterial suspensions and in soil samples decreased hyperbolically with increasing NO up to mixing ratios of about 5 ppmv NO. This behaviour could be modelled by assuming a constant rate of NO production simultaneously with a NO consumption activity that increased with NO until Vmax was reached. The data allowed calculation of the gross rates (P) of NO production, of the rate constants (k), Vmax and Km of NO consumption, and of the NO compensation mixing ratio (mc). In soil, P was larger than Vmax resulting in net NO release even at high NO mixing ratios unless P was selectively inhibited by chlorate + chlorite or by aerobic incubation conditions. In bacteria, Vmax was somewhat larger than P resulting in net NO uptake at high NO mixing ratios. Both P and Vmax were dependent on the supply of electron donor (e.g. glucose). Both in soil (aerobic or anaerobic) and in pure culture, the Km values of NO consumption were in a similar low range of about 0.5–6.0 nM. Anaerobic soil and denitrifying bacteria exhibited mc values of 1.6–2.1 ppmv NO and 0.2–4.0 ppmv NO, respectively.

Diurnal variation of nitric oxide in the upper stratosphere

Two recent measurements of the temporal variation of nitric oxide at constant altitude near 40 km are reported. The observations were made at float altitude with a balloon‐borne chemiluminescence detector together with in situ ozone measurements. The first measurement was made at 44°N on September 17, 1987, at an altitude of 40 km from before sunrise until 1000 LT. The second observation was made at the same latitude on June 18, 1988 at 39 km from 0800 to 1230 LT. The precision of the NO measurements is about 10% at these altitudes, obtained through a more accurate determination of the sample flow rate at pressures down to 2 mbar with a reduced ozone/oxygen flow rate. At an altitude of 40 km, nitric oxide was observed to start increasing very rapidly at sunrise when the solar zenith angle reached about 95°. After the rapid initial buildup, the rate of NO increase stabilized for 3 hours at about 1.2 ppbv/hour. Near 1100 LT at 39 km in summer the NO mixing ratio was observed to become nearly constant. These features of the diurnal variation of NO are in accord with the temporal variation expected from a time‐dependent zero‐dimensional photochemical model. Mixing ratios of NOy and N2O5 have been determined from the measured temporal variation of NO at 39.5±0.5 km, using the photochemical model of Pirre et al. (1989). These derived values of the NOy and N2O5 mixing ratios, 15.5±5.0 ppbv and 1.4±0.6 ppbv, respectively, are in good agreement with other recent measurements by balloon‐borne and space‐borne infrared experiments.

Active nitrogen partitioning and the nighttime formation of N2O5 in the stratosphere: Simultaneous in situ measurements of NO, NO2, HNO3, O3, and N2O using the BLISS diode laser spectrometer

Simultaneous in situ measurements of NO, NO2, HNO3, O3, N2O, pressure, and temperature at 30 km have been made from Palestine, Texas (32°N) on September 13, 1988, using the Jet Propulsion Laboratory Balloon‐Borne Laser In‐Situ Sensor (BLISS) instrument, with the NOAA dual‐channel balloon UV ozone spectrometer on the same gondola. Using tunable diode laser absorption spectroscopy over a long path length, measurements were made during a 24‐hour flight of the daytime concentrations of NO, NO2, and O3 and of the diurnal variation in the concentration of NO2. Postsunset measurements of NO2, made every half minute throughout much of the night, show the NO2 mixing ratio falling from a sunset value of 10.5 ppbv to 5.2 ppbv at night's end. According to the simple identity (d/dt)[NO2] = ‐2k[NO2][O3] for the rate of decay of the NO2 concentration, where k is the rate constant for the reaction between NO2 and O3, an exponential fit to the observed decay agrees with that calculated to better than 10%, with a standard deviation of the fit of only ±3%. Photochemical model calculations constrained to the measured temperature and O3 values, and incorporating both N2O5 and ClONO2 chemistry, predict in detail the observed NO2 diurnal behavior. From the sunset/sunrise difference in the volume mixing ratio of NO2 is derived a value of 2.7±0.4 ppbv for the sunrise N2O5 mixing ratio, in excellent agreement with the model predictions of 2.9 ppbv at this latitude. The measured daytime NO2/NO ratio was found to be in good agreement with model predictions at 30 km. The measured presunset sum NO +NO2 of 10.1±0.8 ppbv agreed well with the measured postsunset NO2 amount of 10.5±0.8 ppbv. Simultaneous measurements of the mixing ratios of HNO3 and postsunset NO2 allow an estimate of total reactive nitrogen, approximated at this time by NO2 + HNO3 + 2(N2O5) + ClONO2, of 16.4±1.2 ppbv at 30 km, and (from an earlier flight) of 13.7±1.7 ppbv at 37 km. Using model predictions incorporating corrections for non‐steady state and for diurnal chemistry, an OH mixing ratio of 8±4 pptv is derived from the measured HNO3/NO2 ratio of 0.72±0.17 at 30 km.

An intercomparison of airborne nitrogen dioxide instruments

Results from an airborne intercomparison of techniques to measure tropospheric levels of nitrogen dioxide (NO2) are discussed. The intercomparison was part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and was conducted during the summer of 1986. Instruments intercompared included a two‐photon nitric oxide (NO) laser‐induced fluorescence system with laser photolysis of NO2 to NO, an NO/O3 chemiluminescence detector using FeSO4 for conversion of NO2 to NO, an NO/O3 chemiluminescence detector with arc lamp photolysis of NO2 to NO, and a tunable diode laser multipath absorption system. All intercomparisons were for NO2 mixing ratios of <200 pptv with most at mixing ratios of <100 pptv. The FeSO4 converter was found to convert peroxyacetyl nitrate (PAN) to NO, resulting in NO2 values a factor of 2–3 higher than reported by the other techniques. Thus the FeSO4 converter data are excluded from the analyses. Intercomparison data were analyzed in various mixing ratio ranges. Good correlation was observed between the remaining three instruments for those data sets which included mixing ratios to 100 or 200 pptv, showing on the average a 30–40% level of agreement among the techniques. However, when the data were restricted to mixing ratios of <50 pptv, little correlation among the measurements was observed. Even though correlations were poor at mixing ratios of <50 pptv, the tunable diode laser system tended to be high compared to data reported by the two‐photon laser and arc lamp chemiluminescence systems, and agreement between the latter two instruments was generally better than 20 pptv with an equal tendency for one to be high relative to the other.

Release of nitric oxide from building stones into the atmosphere

Stone material from the corroding surface of buildings generally released nitric oxide with rates of 0.42–4.2 ng NON h −1 g −1 d.w. despite their large range of moisture, pH and content of ammonium, nitrite and nitrate. The net release rates of NO were independent of the NO mixing ratio of the atmosphere up to 1 ppmv NO. Whereas NO 2 was taken up by all stones tested, uptake of NO was only observed in one out of five types of stone. NO release rates were highest at the stone surface and rapidly decreased in depth lower than 1 cm. NO release persisted for up to >3 months after the stone sample was removed from the building. NO was mainly produced during the biogenic oxidation of ammonium to nitrate at the stone surface which was probably due to endolithic nitrifying bacteria. Chemical decomposition of nitrite to NO and NO 2 was only observed under acidic conditions.

Trends of tropospheric CO, N2O and CH4 as observed at cape point, South Africa

The results of CO, CH4 and N2O measurements performed over several years at the station Cape Point (34°21′S, 18dg29′E), South Africa, are presented. The analytical technique and data filtering procedure are described. The results indicate seasonal variations of the CO and CH4 mixing ratios with maximum values around October and minimum values in February/March. The patterns and the amplitudes of the seasonal variations of both gases compare suprisingly well, indicating interrelations between the source-sink and/or transport mechanisms of CH4 and CO in the Southern Hemisphere. CO measurements performed over a period of 9 years do not show any significant trend of the mean annual CO mixing ratios while the N2O mixing ratios increase at a rate of 0.2% per year for the observation period from 1983 to 1987. The data obtained for CH4 between 1983 and 1987 yield an increase rate of 0.7% per year indicating a reduction of the CH4 increase in the Southern Hemisphere during recent years.

Ozone precursors and ozone photochemistry over eastern North Pacific during the spring of 1984 based on the NASA GTE/CITE 1 airborne observations

Simultaneous, high‐resolution measurements of O3, NO, CO, dew point temperature, and UV flux obtained during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation (GTE/CITE 1) spring 1984 airborne field exercise over the eastern North Pacific Ocean are analyzed. Mid‐tropospheric CO, O3, and NO mixing ratios averaged about 120 parts per billion by volume (ppbv), 50 ppbv, and 10 parts per trillion by volume (pptv), respectively. Statistical analysis of the high‐resolution data indicates the existence of two ozone sources: one related to the downward transport of ozone‐rich air from the upper troposphere and stratosphere and the other to the transport of ozone‐rich air from the continents. Modeling calculations based on these average levels imply that from the surface to about 8 km, photochemical reactions probably supplied a net sink of ozone to the region overlying the eastern North Pacific Ocean during the sampling period. However, because the NO levels measured during the flights were frequently at or near the detection limit of the instruments and because our results are very sensitive to the absolute NO levels and their temporal variability, our conclusion must be considered provisional.

Microbial production and uptake of nitric oxide in soil

Fluxes of NO from three different soils have been studied by a flow-through system in the laboratory as a function of gas flow rate, of NO mixing ratio, and of incubation conditions. The dependence of net NO fluxes on gas flow rates and on NO mixing ratios could be described by a simple model of simultaneous NO production and NO uptake. By using this model, rates of gross NO production, rate constants of NO uptake, and NO compensation mixing ratios could be determined as function of the soil type and the incubation condition. Gross NO production rates were one to two orders of magnitude larger under anaerobic than under aerobic conditions. NO uptake rate constants, on the other hand, were only 5–8 times larger so that the compensation mixing ratios of NO were in a range of about 1600–2200 ppbv under anaerobic and of about 50–600 ppbv under aerobic conditions. The different soils exhibited similar NO uptake rate constants, but the gross NO production rate and compensation mixing ratio was significantly higher in an acidic (pH 4.7) sandy clay loam than in other less acidic soils. Experiments with autoclaved soil samples showed that both NO production and NO uptake was mainly due to microbial metabolism.

Microbial production and uptake of nitric oxide in soil

Fluxes of NO from three different soils have been studied by a flow-through system in the laboratory as a function of gas flow rate, of NO mixing ratio, and of incubation conditions. The dependence of net NO fluxes on gas flow rates and on NO mixing ratios could be described by a simple model of simultaneous NO production and NO uptake. By using this model, rates of gross NO production, rate constants of NO uptake, and NO compensation mixing ratios could be determined as function of the soil type and the incubation condition. Gross NO production rates were one to two orders of magnitude larger under anaerobic than under aerobic conditions. NO uptake rate constants, on the other hand, were only 5–8 times larger so that the compensation mixing ratios of NO were in a range of about 1600–2200 ppbv under anaerobic and of about 50–600 ppbv under aerobic conditions. The different soils exhibited similar NO uptake rate constants, but the gross NO production rate and compensation mixing ratio was significantly higher in an acidic (pH 4.7) sandy clay loam than in other less acidic soils. Experiments with autoclaved soil samples showed that both NO production and NO uptake was mainly due to microbial metabolism.

Approximation for the vibrational excitation of middle atmospheric NO by upwelling radiation

A plane-parallel approximation using FASCODE to calculate upward and downward IR flux density and angle-averaged radiance is described and tested against results that account for planetary curvature. The method is further developed to calculate the excitation of NO(v = 1) due to absorption of upwelling radiation in the earth's atmosphere. The algorithm is applied to a standard set of atmospheric models, in addition to typical and extreme desert atmospheric models which are included to maximize the effect. The results of this work show that upwelling radiation typically contributes <2.5% to the total NO(v = 1) excitation in the midstratosphere rises to ~5% at 50 km and becomes increasingly significant at higher altitudes. It is shown that in the mesosphere excitation due to upwelling and solar radiation become important compared to the dominant processes, thermal collisions, and chemical excitation. An approximate technique utilizing meteorological data, namely, tropospheric temperature, pressure, and humidity profiles, is developed to estimate the excitation of NO(v = 1) in the middle atmosphere. This technique would facilitate the retrieval of the NO mixing ratio from earthlimb emission data, as might be obtained from a satellite-borne limb sounding experiment, since it could be used to approximate the contribution of upwelling radiation to the NO(v = 1) non-LTE vibrational temperature efficiently.

Measurements of nitric oxide between 0–12 km altitude and 67°N to 60°S latitude obtained during STRATOZ III

Using a chemiluminescent detector, vertical profiles of NO were measured during the STRATOZ III mission from June 4–26, 1984. The mission's flight track started close to Paris, went west across the North Atlantic, south along the east coast of North America and the west coast of South America. It returned north along the east coast of South America, crossed the Atlantic around the equator and continued north along the west coast of North Africa and continental Europe. It covered the latitudes between 67°N and 60°S and the altitudes between 0 and 12 km. The coastal profiles in the northern hemisphere and in the tropics exhibited a C shape, with higher NO concentration values in the planetary boundary layer and the upper troposphere, whereas the measurements over the ocean showed low values in the upper troposphere. The NO mixing ratios in the southern hemisphere, south of 20°S latitude, were lower than in the northern latitudes and showed little increase in the upper troposphere. The two‐dimensional NO distribution along the flight track is derived, and the possible sources of the NO in the high troposphere are briefly discussed.

Stratospheric nitrogen dioxide concentrations as determined from limb brightness measurements made on June 17, 1983

A multiwavelength spectrometer with limb‐scanning optics was developed to make NO2 measurements in the stratosphere. The instrument observes light scattered by aerosol particles and air molecules and measures the differential attenuation of light at different wavelengths by NO2. A vertical profile of NO2 was determined from the brightness measurements, using the results of a single scattering model. The instrument was flown from Palestine, Texas, and observed the stratosphere from an altitude of 33 km at 32°N, 98°W for a period of several hours on the afternoon of June 17, 1983. The mixing ratio of NO2 was observed to be (3.5±0.8) parts per billion by volume (ppbv) at 28 km, in reasonable agreement with solar occultation measurements. The time rate of change of the NO2 concentration at 28 km is estimated at (0.18±0.06) ppbv per hour at 2200 coordinated universal time (CUT).

Diurnal variation of nitric oxide at 32 km: Measurements and interpretation

On September 19–20 and October 4, 1985, in situ measurements of nitric oxide and ozone were carried out on board balloons launched from Aire sur l'Adour (44°N, 0°W) in France as a part of the Middle Atmosphere Program Global Budget of Stratospheric Trace Constituents NOx campaign. On September 19 a daytime NO profile from 6 to 33 km and the variation of NO in the afternoon at a float altitude of about 32 km were measured precisely. In the afternoon, when the solar zenith angle was between 48° and 70°, NO concentration was fairly stable, probably to within 10%. The slow decrease of NO near sunset at solar zenith angles larger than 80° was observed. A calculation assuming photochemical equilibrium between NO and NO2 has shown that the decay of NO toward sunset can be explained mainly by the decrease of the photodissociation rate of NO2 at large solar zenith angles. On October 4 the variation of NO at an altitude of about 33 km was measured for 2.5 hours after sunrise. Following the rapid buildup, which takes place for 30 min after visible sunrise, NO increases at a rate of approximately 1.2 parts per billion by volume (ppbv) per hour. From the rate of increase in NO in the morning, the N2O5 mixing ratio at sunrise at 33 km has been estimated to be 3.9±1.5 ppbv.

Extremely low N2O concentrations in the springtime stratosphere at McMurdo Station, Antarctica

Nitrous oxide is an important tracer of transport, as well as the ultimate source gas for NOx in the stratosphere. Its calculated chemical lifetime in the troposphere and lower stratosphere is longer than transport timescales worldwide, so that its mixing ratio is not expected to be strongly dependent on latitude or season. However, we have now made frequent measurements of stratos-pheric N2O using the Stony Brook millimetre-wave remote sensing spectrometer at McMurdo Station, Antarctica, as part of the investigation of the 'ozone hole'1 and find N2O mixing ratios that are less than 1/5 at 20km, and less than 1/10 at 25km compared to values measured during the Antarctic summer. The observed mixing ratios are also much less than those predicted by global-scale models of stratospheric chemistry and dynamics. As the N2O signal remained very weak when McMurdo was at the edges of the ozone hole and snowed no signs of recovering during October, we conclude that the geographical and temporal extent of the region of low N2O is comparable to, or greater than that of the ozone hole. Our results argue against theories that require springtime upwelling to explain the Antarctic ozone hole, and suggest that the air in the Antarctic lower stratosphere during late winter and early spring has been subjected to considerable down-ward transport.

A ground‐based intercomparison of NO, NOx, and NOy measurement techniques

At a site near Boulder, Colorado, simultaneous atmospheric measurements were made of NO, NOx, and NOy in a field intercomparison of instruments involving two currently employed techniques of NOx and NOy measurement. Both NOy instruments depended upon the reduction of the NOy species to NO with detection by chemiluminescence, but different catalysts were employed for the reduction: (1) a gold catalyst (with addition of 0.3% CO) at 300°C, or (2) a molybdenum catalyst at 400°C. The two systems of NOx detection involved (1) photolysis of NO2, and (2) reduction of NO2 by solid ferrous sulfate. Several times during the intercomparison the response to calibrated samples of reference compounds NO, NO2, PAN, HNO3, n‐propyl nitrate (NPN), and NH3 was measured. From the results the following conclusions were made: (1) The two NO instruments agreed on NO mixing ratios that were measured during the daytime hours over a range from the limits of detection to 35 parts per billion by volume (ppbv), (2) the two NOy instruments gave similar estimates of NOy in ambient air over a wide range of mixing ratios (0.4–10 ppbv), and (3) the ferrous sulfate converter used for NOx detection showed a significant interference from NPN and PAN.

Helium-cooled balloon-borne infrared experiment for measurements of stratospheric trace gas emissions

A helium-cooled IR spectrometer with a diffraction-limited telescope was launched on 23 Sept. 1983 from Aire-sur-l'Adour (France) as part of the MAP/Globus 1983 campaign. The float altitude of the balloon was 38 km. Limb scan measurements of atmospheric emissions were taken in the 5.5-19-microm wavelength region. The measurements were performed ~1 h before sunrise. From several spectral features volume mixing ratios of NO(2), H(2)O, CH(4), HNO(3), O(3), and N(2)O were derived.

Stratospheric NO profiles measured simultaneously using two chemiluminescent balloon-borne sondes

During the 1983 MAP/GLOBUS campaign at Aire sur 1'Adour, France, an intercomparison of two balloon-borne chemiluminescent NO detectors was carried out. Stratospheric NO profiles measured simultaneously by the NO sonde of the Institute of Atmospherics (RIA) of Nagoya University and the NO/NO 2 sonde developed at the Max-Planck-Institut für Aeronomie (MPAE) are reported. Above 20 mb (about 26 km), both data sets show very good agreement, with daylight NO mixing ratios increasing from 1.5 ppbV at 26 km to 9 ppbV at 33 km altitude, with only small diurnal variations observed for solar zenith angles of less than 57°. Some preliminary NO 2 data measured by the MPAE instrument by diverting the air flow through a hot metal converter are also presented. The results are compared with predictions from a diurnal variation model.

Measurements of nitric oxide in the boundary layer and free troposphere over the Pacific Ocean

Measurements of NO and O3 are presented from 13 aircraft flights made over the Pacific Ocean in the autumn of 1983 during one phase of the NASA Global Tropospheric Experiment (GTE). All of the flights were made between 15° and 42°N and from the coast of California to west of the Hawaiian Islands. Within the upper marine boundary layer the median daytime mixing ratio of NO was near 1 part per trillion by volume (pptv). As well, values of NO less than 10 pptv were often observed up to altitudes near 6 km. Thus for the location and season of the measurements, a net photochemical destruction of O3 would be anticipated for the boundary layer region and to altitudes of 2–3 km. At higher altitudes of 7–11 km in the free troposphere, larger mixing ratios and greater variability were usually observed for NO. Both features are consistent with observed examples of injection of NO and O3 from the lower stratosphere and with the injection of NO from towering, electrically active, cumulonimbus clouds.

On the origins of night-time NO at a rural measurement site

Mixing ratios for NO and NO 2 were measured during 1980/1981 at Deuselbach, a rural site in Germany. The data are analyzed with regard to the occurrence of nocturnal NO signals and their origins. Anthropogenic influences arising from road traffic and home heating activities are identified by their dependence on wind direction. An additional non-directional component is found to exist. It shows up most frequently in summer and when it occurs, the NO mixing ratio increases with rising temperature indicating a biological origin of night-time NO. The temporal behavior of night-time NO is usually correlated with that of CO 2 but anticorrelated to that of O 3. This shows that NO is brought upwards to the air intake of the NO x monitor from lower levels and that the source of the non-directional component of nocturnal NO is the earth's surface. The release of NO from soils is known from other work and this process is probably also responsible for the present observations. A flux estimate agrees with soil fluxes reported by other authors. The accumulation of NO in the surface air layer under stagnant conditions leads to the appearance of a morning peak of NO after sunrise when increased vertical mixing brings NO rich air up to the monitoring level. During summer, the morning peak may override the NO peak expected to occur at noon due to the photodissociation of NO 2.

An analysis of preliminary SAGE II data on ozone and NO 2

Zonal mean mixing ratios of ozone and NO 2 measured by SAGE II on several days in March and April, 1985 are compared against zonal means for this time of year previously measured by SAGE I, SBUV, and LIMS. After allowing for calculated diurnal variations of these gases, agreement within 15% is found for ozone and 20% for NO 2. It is noted that the profile error bars given on the SAGE II data tapes need to be carefully interpreted and that the measured tropical variances suggest that these error bars are being somewhat overestimated. Planetary waves in both ozone and NO 2 in the middle stratosphere should be derivable from the SAGE II measurements.