CO Tracers Research Articles

Lagrangian transport model forecasts and a transport climatology for the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) measurement campaign

On the basis of Lagrangian tracer transport simulations this study presents an intercontinental transport climatology and tracer forecasts for the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) aircraft measurement campaign, which took place at Monterey, California, in April–May 2002 to measure Asian pollution arriving at the North American West Coast. For the climatology the average transport of an Asian CO tracer was calculated over a time period of 15 years using the particle dispersion model FLEXPART. To determine by how much the transport from Asia to North America during ITCT 2K2 deviated from the climatological mean, the 15‐year average for April and May was compared with the average for April and May 2002 and that for the ITCT 2K2 period. It was found that 8% less Asian CO tracer arrived at the North American West Coast during the ITCT 2K2 period compared to the climatological mean. Below 8‐km altitude, the maximum altitude of the research aircraft, 13% less arrived. Nevertheless, pronounced layers of Asian pollution were measured during 3 of the 13 ITCT 2K2 flights. FLEXPART was also successfully used as a forecasting tool for the flight planning during ITCT 2K2. It provided 3‐day forecasts for three different anthropogenic CO tracers originating from Asia, North America, and Europe. In two case studies the forecast abilities of FLEXPART are analyzed and discussed by comparing the forecasts with measurement data and infrared satellite images. The model forecasts underestimated the measured CO enhancements by about a factor of 4, mainly because of an underestimation of the Asian emissions in the emission inventory and because of biomass‐burning influence that was not modeled. Nevertheless, the intercontinental transport and dispersion of pollution plumes were qualitatively well predicted, and on the basis of the model results the aircraft could successfully be guided into the polluted air masses.

Global chemical weather forecasts for field campaign planning: predictions and observations of large-scale features during MINOS, CONTRACE, and INDOEX

Abstract. The first global tropospheric forecasts of O3 and its precursors have been used in the daily flight planning of field measurement campaigns. The 3-D chemistry-transport model MATCH-MPIC is driven by meteorological data from a weather center (NCEP) to produce daily 3-day forecasts of the global distributions of O3 and related gases, as well as regional CO tracers. This paper describes the forecast system and its use in three field campaigns, MINOS, CONTRACE and INDOEX. An overview is given of the forecasts by MATCH-MPIC and by three other chemical weather forecast models (EURAD, ECHAM, and FLEXPART), focusing on O3 and CO. Total CO and regional CO tracers were found to be the most valuable gases for flight planning, due to their relatively well-defined anthropogenic source regions and lifetimes of one to a few months. CO was in good agreement with the observations on nearly all the flights (generally r > 0.7, and the relative RMS differences for the deviations from the means was less than 20%). In every case in which the chemical weather forecasts were primarily responsible for the flight plans, the targeted features were observed. Three forecasted phenomena are discussed in detail: outflow from Asia observed in the Mediterranean upper troposphere during MINOS, outflow from North America observed in the middle troposphere over northern Europe during CONTRACE, and the location of the "chemical ITCZ'' over the Indian Ocean during INDOEX. In particular it is shown that although intercontinental pollution plumes such as those observed during MINOS and CONTRACE occur repeatedly during the months around the campaigns, their frequency is sufficiently low (~10--30% of the time) that global chemical weather forecasts are important for enabling them to be observed during limited-duration field campaigns. The MATCH-MPIC chemical weather forecasts, including an interface for making customized figures from the output, are available for community use via http://www.mpch-mainz.mpg.de/~lawrence/forecasts.html.

Heavy metals in urban soils: a case study from the city of Palermo (Sicily), Italy

Concentrations of V, Mn, Cd, Zn, Ni, Cr, Co, Cu, Pb, Hg and Sb were measured on 70 topsoil samples collected from green areas and parks in the city of Palermo (Sicily) in order to: (1) assess the distribution of these heavy metals in the urban environment; (2) discriminate natural and anthropic contributions; and (3) identify possible sources of pollution. Mineralogy, physico-chemical parameters, and major element contents of the topsoils were determined to highlight the influence of ‘natural’ features on the heavy metal concentrations and their distribution. Medians of Pb, Zn, Cu and Hg concentrations of the investigated urban soils are 202, 138, 63 and 0.68 mg kg −1, respectively. These values are higher, in some case by different orders of size, than those of unpolluted soils in Sicily that average 44, 122, 34 and 0.07 mg kg −1. An ensemble of basic and multivariate statistical analyses (cluster analysis and principal component analysis) was performed to reduce the multidimensional space of variables and samples, thus defining two sets of heavy metals as tracers of natural and anthropic influences. Results demonstrate that Pb, Zn, Cu, Sb and Hg can be inferred to be tracers of anthropic pollution, whereas Mn, Ni, Co, Cr, V and Cd were interpreted to be mainly inherited from parent materials. Maps of pollutant distribution were constructed for the whole urban area pointing to vehicle traffic as the main source of diffuse pollution and also showing the contribution of point sources of pollution to urban topsoils.

Improvement of a wind-tunnel sampling system for odour and VOCs

Wind-tunnel systems are widely used for collecting odour emission samples from surface area sources. Consequently, a portable wind-tunnel system was developed at the University of New South Wales that was easy to handle and suitable for sampling from liquid surfaces. Development work was undertaken to ensure even air-flows above the emitting surface and to optimise air velocities to simulate real situations. However, recovery efficiencies for emissions have not previously been studied for wind-tunnel systems. A series of experiments was carried out for determining and improving the recovery rate of the wind-tunnel sampling system by using carbon monoxide as a tracer gas. It was observed by mass balance that carbon monoxide recovery rates were initially only 37% to 48% from a simulated surface area emission source. It was therefore apparent that further development work was required to improve recovery efficiencies. By analysing the aerodynamic character of air movement and CO transportation inside the wind-tunnel, it was determined that the apparent poor recoveries resulted from uneven mixing at the sample collection point. A number of modifications were made for the mixing chamber of the wind-tunnel system. A special sampling chamber extension and a sampling manifold with optimally distributed sampling orifices were developed for the wind-tunnel sampling system. The simulation experiments were repeated with the new sampling system. Over a series of experiments, the recovery efficiency of sampling was improved to 83-100% with an average of 90%, where the CO tracer gas was introduced at a single point and 92-102% with an average of 97%, where the CO tracer gas was introduced along a line transverse to the sweep air. The stability and accuracy of the new system were determined statistically and are reported.

Architectural and physiological heterogeneity within the synflorescence of the pseudoviviparous grass Poa alpina var. vivipara L.

Many biotypes of the northern-hemisphere Arctic-Alpine grass Poa alpina L. reproduce asexually via prolification of the spikelet axis to produce dehiscing shoots. Although capable of photosynthesis, the source-sink characteristics of these synflorescence systems are unknown, including the degree to which plantlets from different regions of the synflorescence are capable of providing for their own carbon requirements, or contributing to other sinks. Photosynthetic rates within the paracladial zone, as determined by infrared gas analysis (IRGA), exceeded respiratory rates by 3-4-fold. (14)CO(2) tracer studies determined that the paracladial zone was not only as efficient at fixing carbon as the youngest fully expanded leaf (per unit dry weight), but that both organs exported carbon mainly basipetally (cf. extensive acropetal export from this leaf in seminiferous grasses). Distal plantlets of the paracladial zone fixed approximately 20% more (14)CO(2) than did proximal plantlets. This was by virtue of their greater dry weight. At dehiscence, 'distal' plantlets were more likely to become established, and possessed relative growth rates more than 10 times those of 'proximal' plantlets. Paracladial heterogeneity was also apparent as an increased proportion of aborted spikelets on proximal paracladia. The possible causes of this heterogeneity are discussed.

A new method for determining the CO to H2 conversion factor for translucent clouds

In this paper we describe a new technique for obtaining the conversion factor between the molecular hydrogen column density and the CO(J = 1-0) integrated antenna temperature. This factor, typically known as X(sub CO) is often to be of order a few times 10(exp 20)/sq cm/K km/s) for the molecular clouds in the Galaxy and is one of the primary means of determining the molecular cloud mass from CO observations. However, for the low-extinction interstellar clouds known as the translucent molecular clouds, estimates of X(sub CO) vary by up to a factor of 60 depending on the object and techniques employed to calibrate X(sub CO). Since the cloud mass is directly proportional to X(sub CO) uncertainties in mass estimates of translucent clouds can be more than an order of magnitude. We calibrate the H2 content in translucent clouds by using the linear relationship between the CH and H2 column densities. The CH column density is readily determined from observations of the CH ground-state hyperfine main-line transition at 3335 MHz. Using CH as a surrogate tracer for H2 and CO(J = 1-0) observations of a sample of translucent and dark molecular clouds, we find a wide variation in values for X(sub CO). For translucent clouds, X(sub CO) ranges from 0.3 to 6.8 x 10(exp 20) and for dark clouds the values range from 0.8 to 8.6. Although the average values for both types of cloud are similar to the canonical value determined for the Galactic molecular cloud ensemble (2-4 x 10(exp 20)), the scatter in individual X(sub CO) values may indicate that X(sub CO) for a given translucent cloud cannot be determined a priori and must be obtained for each cloud so that a reliable mass determination may be made.

Dust and gas emission in Barnard 5

The relationships among IR emission, CO isotope intensities, and visual extinction in the molecular cloud Barnard 5 are studied in order to evaluate various candidates as mass tracers or molecular material and to determine the properties of dust grains emitting at 60 and 100 microns. The results establish a strong correlation between the 100 micron dust opacity and the (C-13)O column density. This relationship should allow for tracing the molecular gas with the 100 and 60 micron emission in regions without strong embedded heat sources. For single homogeneous clouds, (C-13)O is the best CO tracer of mass and gives the best estimate of virial mass. The mass of B5 estimated from the (C-13)O luminosity is 930 solar masses, while that of the core and dense fragments is only 200 solar masses. An algorithm is developed for calculating the virial mass of a cloud based on observation of optically thin lines.

Effect of diesel vehicles on visibility in California

The effect of diesel vehicle elemental carbon on visibility in California is estimated for 1980 and projected to the early 1990's. An emissions budget model indicates that heavy-duty diesel trucks contributed nearly one-half of statewide elemental carbon emissions in 1980 and about 5–15% of statewide light extinction (visibility reduction). A lead tracer model indicates somewhat larger extinction contributions from heavy-duty diesel trucks, about 5 to 25% statewide in 1980. Even greater visibility impacts (too large to be reasonable) are suggested by a CO tracer model. Because of increased diesel usage — due to both overall traffic growth and partial conversion of the vehicle fleet to diesels (10% of light-duty, 20% of medium-duty, and 60% of currently gasoline heavy-duty) — visibility in California is projected to decrease significantly (about 9 to 35%) from 1980 to the early 1990's under a “no control” scenario. Diesel vehicle elemental carbon would then contribute 13 to 40% of statewide visibility reduction. Even in the early 1990's, heavy-duty trucks would account for about three-fourths of the emissions from the entire diesel fleet. The most uncertain aspect of the conclusions is the overall magnitude of the visibility effect predicted by the emission budget and Pb tracer models. The partition of visibility impacts among light-, medium-, and heavy-duty vehicles is more definite. The conclusions are rather insensitive to reasonable changes in the assumptions regarding emission factors, traffic growth, and dieselization percentages. The findings indicate that, in order to be effective in protecting visibility, the current California standards for light- and medium-duty vehicles would have to be extended to include regulations for heavy-duty trucks.

Studying local air pollution with CO tracers

Where chimney stacks are of only moderate height, nearby obstructions to windflow can cause unacceptable air pollution near ground level in the immediate vicinity. Studies of this phenomenon are turning to the use of carbon monoxide tracers, which must be handled with care. How this has been done economically with model buildings in a wind tunnel at the University of Sydney, Australia, is described in this article by the Senior Lecturer in Architectural Science at the University.

Dynamics of the Gas in Spiral Galaxies

AbstractThe dynamics of the gaseous component in disk-shaped galaxies is thought to play an important governing role in star formation, molecule formation, and the degree of development of spiral structure. The prospect that density waves and galactic shock waves are present on the large-scale has received support in recent years from a variety of observational studies. Large-scale shocks provide a most promising mechanism for driving star-forming and molecule-forming events on the scales of many kpc along spiral arms. Such shocks may also govern the kinematics and relative distribution of various galactic tracers. This is particularly apparent in M81 and other external spirals, because of our “bird’s-eye-view” perspective, and for the tracers of HI and CO in our own Galaxy. Comparison of the CO observations with model simulations based on the precepts of the density wave theory shows that these precepts are supported by several observational results.

Vibrational relaxation of shock-heated N2 by atomic oxygen using the ir tracer method

We have studied the effects of oxygen atoms on the vibrational relaxation of shock-heated N2 over the temperature range from 1200 to 3000 °K, using the CO tracer technique. The measured relaxation times pτN2–O vary from 0.8 to 2 atm · μsec in this range with an uncertainty of ± 50%, in excellent agreement with existing high-temperature shock tube and low-temperature flow tube results. The weak temperature dependence of all these results is in marked contrast to theoretical predictions. Some limited measurements of the relaxation of CO by oxygen atoms yield values of pτCO–O of approximately 0.04 atm · μsec, in good agreement with other recent measurements. This rate is approximately 25 times as fast as the N2–O rate and, coincidentally, is approximately the same as that for the relaxation of O2 by O atoms. The greater rapidity of the CO–O and O2–O relaxation, compared with that of N2–O, may be the result of atom-exchange processes in the former cases.

Measurements of Temperatures of Vibrationally Excited N2

A comparison of the vibrational and rotational temperatures of microwave discharged N2 as measured by the CO tracer and the Penning ionization with He(23S) techniques has been performed in a flow tube apparatus. A vibrational temperature range of 1000–3000°K was covered at a kinetic temperature of ∼350°K. A detailed analysis of each technique is presented. The effect of pressure quenching of the N2+(1−) radiation occurring in the Penning ionization technique and the effect of vibrational temperature gradient across the flow tube in the CO tracer technique are discussed. Because of the good agreement of vibrational temperatures deduced from the two techniques, it is concluded that the Treanor-Teare relationship between the vibrational temperatures of diatomic gases in binary mixture in the V–V quasiequilibrium regime is valid. This work represents the first experimental confirmation of this relationship. The agreement of rotational temperatures implied by the N2+ and CO spectra indicates that the rotational distribution in BN2+(v′) is not significantly distorted from the N2 equilibrium distribution by the heavy He(23S) impact.

Diffusion of Iron, Cobalt, and Nickel in Single Crystals of Pure Copper

The rates of diffusion of radioactive tracers of Fe, Co, and Ni in single crystals of pure copper have been measured as a function of temperature from about 700 to 1075 deg C. The results, obtained by the tracer-sectioning technique, are as follows: D/sub Fe yields Cu/ = 1.4 exp(-51,800/RT); D/sub Co yields Cu/ = 193 exp(--54,100/RT); D/sub Ni yields Cu/ = 2.7 exp(--56,500/RT); all in units of cm/sup 2/sec. An exploratory measurement for a Mn tracer in copper was made at 1069 deg C with the result D = 1.49 x 10/sup -8/ cm/sup 2/sec. The results of several current theoretical calculations are compared with the present data: Wert and Zener's correlation of D/sub O/ and Q is supported by the present work; the basic qualitative prediction of Lazarus' screening theory is borne out by the present results, although the extent of the detailed agreement is not clear at this time. The experimental data yielded unexpectedly large diffusion coefficients at low temperatures in some cases and several possible causes are considered. Finally, a new experimentel method is described for determining diffusion coefficients with tracers emitting only very low--energy particles. (auth)