Tropospheric OH Concentrations Research Articles

Cloud Albedo, Greenhouse Effects, Atmospheric Chemistry, and Climate Change

Changes in global atmospheric chemistry and climate are taking place as a result of observed trends in long-lived species such as CO2, CH4, N2O, and the CFCs. The continuation of these trends is expected to eventually lead to a major atmospheric warming that might profoundly affect the society we live in. Trends in short-lived species such as NOx and SOx are also suspected. These trends are not as well established, because the shorter-lived species vary spatially and temporally. Trends in NOx would be expected to lead to increases in tropospheric ozone that would add to the warming created by the other greenhouse gases. Trends in NOx could also alter tropospheric OH concentrations that could lead to changes in CH4 and some of the CFCs. On the other hand, increases in sulfur emissions may alter cloud optical properties. The changes in cloud optical properties could possibly offset the warming expected from increases in greenhouse gases, depending on the role of natural oceanic sulfur emissions. This paper summarizes recent research in these areas and the interactions of climate and atmospheric chemistry.

Measurement of tropospheric OH concentrations by laser long-path absorption spectroscopy

Measurement of tropospheric OH concentrations by laser long-path absorption spectroscopy

Responses of the tropospheric ozone and odd hydrogen radicals to column ozone change

The response of tropospheric ozone to a change in solar UV penetration due to perturbation on column ozone depends critically on the tropospheric NO x (NO+NO2) concentration. At high NO x or a polluted area where there is net ozone production, a decrease in column ozone will increase the solar UV penetration to the troposphere and thus increase the tropospheric ozone concentration. However, the opposite will occur, for example, at a remote oceanic area where NO x is so low that there is net ozone destruction. This finding may have important implication on the interpretation of the long term trend of tropospheric ozone. A change in column ozone will also induce change in tropospheric OH, HO2, and H2O2 concentrations which are major oxidants in the troposphere. Thus, the oxidation capacity and, in turn, the abundances of many reduced gases will be perturbed. Our model calculations show that the change in OH, HO2, and H2O2 concentrations are essentially independent of the NO x concentration.

Measurement of tropospheric OH concentrations by laser long-path absorption spectroscopy

Tropospheric hydroxyl (OH) radical concentrations were measured in summer 1987 in Jiilich by broadband laser long-path absorption (laser-LPA) spectroscopy observing the Q 1 (2), Q 2 1 (2).Q 1 (3).Q 2 1 (3). and P 1 (1) rotational absorption lines around 308 nm. The measurement technique was improved using a multichannel spectrometric detector to record the OH absorption spectra. Now a much wider spectral interval can be observed at high resolution; thus, registration and correction of overlapping absorption features of interfering trace gases is improved. Simultaneous to the OH measurements, the concentrations of nitrogen dioxide (NO 2 ), formaldehyde (HCHO), and sulfur dioxide (SO 2 ) were monitored by a second LPA spectrometer. Ozone (O 3 aerosol concentrations, meteorological parameters, and absolutely calibrated photolysis frequencies of O 3 and NO 2 were also recorded. Carbon monoxide (CO), methane (CH 4 ), and light hydrocarbons were determined by gas chromatographic analysis. OH concentrations ranged up to 6.8.10 6 molecules/cm 3 . At one day in July, an 'asymmetric' diurnal profile of the OH concentration was observed, which could be qualitatively explained by a strong decrease in the NO 2 concentration during the morning hours. DOI: 10.1111/j.1600-0889.1988.tb00115.x

Measurements of tropospheric OH concentrations: A comparison of field data with model predictions

Using long path UV absorption spectroscopy we have measured OH concentrations close to the earth's surface. The OH values observed at two locations in Germany during 1980 through 1983 range from 0.7×106 to 3.2×106 cm-3. Simultaneously we measured the concentrations of O3, H2O, NO, NO2, CH4, CO, and the light non methane hydrocarbons. We also determined the photolysis rates of O3 and NO2. This allows calculations of OH using a zero dimensional time depdendent model. The modelled OH concentrations significantly exceed the measured values for low NO x concentrations. It is argued that additional, so far unidentified. HO x loss reactions must be responsible for that discrepancy.

A laser optical method for the determination of tropospheric OH concentrations

A long-path absorption procedure for the determination of tropospheric OH concentrations is described in detail. Initial measurements using this method were carried out in Frankfurt a. M. By including in the evaluation the visible radiation of a frequencydoubled dye laser used in the measurements, it was possible to mathematically reduce the signal fluctuations caused by the scattering and density fluctuations of tropospheric air. The resulting detection limit was 3×106 OH per cm3. SO2 concentrations which had to be simultaneously determined in order to eliminate an interference effect, could be detected in the range of 1–40 ppb on the absorption path.

The Atmospheric Lifetime Experiment: 5. Results for CH3CCl3 based on three years of data

We present gas chromatographic determinations of the concentrations of CH3CCl3 at Adrigole (Ireland), Cape Meares (Oregon), Ragged Point (Barbados), Point Matatula (American Samoa), and Cape Grim (Tasmania) for the 3‐year period July 1978 through June 1981. The determinations involve approximately four measurements each day with on‐site calibration. The absolute values and trends for these observed concentrations are interpreted in terms of the industrial production, global circulation rate, and atmospheric lifetime of CH3CCl3 by using an optimal estimation technique that incorporates a nine‐box model of the atmosphere. The globally and annually averaged trend in the lower troposphere at the midpoint of the second year of the experiment is 8.7% per year, and the inferred global atmospheric content of CH3CCl3 at this midpoint is 2.58×109kg. The global atmospheric lifetime deduced by using the observed trends and global content together with current estimates of industrial CH3CCl3 emissions is years. This deduced lifetime is sufficiently long to imply that the observed variability in the data on seasonal and shorter time scales must be dominated by meteorological (and perhaps industrial emission) variabilities rather than by spatial and temporal variations in the rate of chemical destruction of CH3CCl3 by OH. However, the observed variations on annual and longer time scales are sensitive to the spatially and temporally averaged OH concentrations. In particular, the globally averaged tropospheric OH concentration compatible with the above‐deduced CH3CCl3 lifetime is (5 ± 2) × 105 molecule cm−3; in reasonable agreement, for example, with the value of ( ) × 105 molecule cm−3 deduced by Volz et al. (1981) from measurements of CO. Our results are sensitive to constraints imposed on uncertainties in the CH3CCl3 emissions and absolute mixing ratios. If we decrease emissions by ≲8% in the years 1976–1978 and increase emissions in 1979–1981 to compensate, and if absolute mixing ratios are decreased by about 18%, then the best estimate of the lifetime from our data decreases to 6.5 years.

Seasonal and latitudinal variation of 14CO and the tropospheric concentration of OH radicals

Ground‐based measurements of the concentration of 14CO are reported. The data exhibit a well‐defined seasonal variation at mid‐latitudes with a maximum of 25 ± 2 molecule cm−3 during winter and a minimum of 11 ± 1 molecule cm−3 during summer. The measurements also indicate a strong latitudinal variation, with the lower concentrations occurring in the tropics. The data are interpreted using a 2‐D time‐dependent model. To balance the sources of both 14CO and 12CO, an average tropospheric OH concentration of (6.5‐2+3) × 105 molecule cm−3 is required. In addition, the 12CO production rate from biological processes including the oxidation of nonmethane hydrocarbons is found to be 1250 × 1012 g CO yr−1.

Optical Measurements of Tropospheric Hydroxyl with Lasers

Abstract The application of laser induced fluorescence (LIF) in the uv to monitor tropospheric OH concentrations is limited for several reasons. In general the sensitivity of this method increases with the laser intensity. But at the low OH concentrations present in the atmosphere the beginning nonlinearity of the absorption (saturation effect) severely restricts the use of higher laser intensities. The high sensitivity of the LIF technique can be further compromised by the presence of an OH interference signal. This signal is generated by the monitoring laser light itself from laser photolysis of ambient ozone and the succeeding reaction of the photolysis product O (1D) with water to produce hydroxyl radicals. The results of the calculations are presented in a diagram from which the range of laser parameters can be deduced, which can be applied with confidence to monitor OH by the LIF method. The maximum number of signal counts for these working conditions is in the range of 10-3 per laser pulse.

Is UV laser induced fluorescence a method to monitor tropospheric OH?

Calculations are presented which demonstrate the important interference of laser generated OH in ambient air with tropospheric OH if LIF technique is used. A comparison of previous measurements with the results of our calculations shows that the measured tropospheric OH concentration is within the order of magnitude of laser generated OH.

Average concentrations of OH in the troposphere, and the budgets of CH 4, CO, H 2 and CH 3CCl 3

An average tropospheric OH concentration in the Northern Hemisphere of about 3 × 105 cm −3 is not in disagreement with present photokinetic information. This has important implications for the tropospheric budgets of CH 4, CO, H 2 and CH 3CCl 3. Present concentrations of CH 4 and H 2 in the atmosphere may be substantially larger than those prevailing during the pre‐industrial era, implying also an increase in H 2O concentrations and a decrease in ozone concentrations in the upper stratosphere. Accepting this estimate of an OH concentration and an important CO sink at the ground (Seiler, 1974), there must be additional sources of CO than considered in presently evaluated budgets.

Possible effects on fropospheric O 3 and OH due to No emissions

The effects of NO emissions on non‐urban tropospheric ozone and OH concentrations are investigated. It is shown that ozone is not likely to increase with the increase in the injection of NO alone into an otherwise clean ambient atmosphere. Ambient OH concentrations would be increased by NO emissions through the NO + HO 2 reaction.