Atmospheric Environment. Part A. General Topics最新文献

Galvanized steel specimens varying in size, shape, orientation angle and previous exposure history (weathered specimens) were exposed at Research Triangle Park, NC, in the absence of natural precipitation. The soluble corrosion products were assumed to represent the effects of dry deposition of airborne substances. The statistical analysis of their variability in relation to atmospheric conditions suggested that these substances included sulfur dioxide, nitric acid, hydrochloric acid, and calcium (presumably from coarse particles). The specimen characteristic most influencing inferred dry deposition was previous exposure history. Deposition of gases depended on surface condition (wetness), wind speed, temperature, and to a lesser extent, orientation angle. Deposition of particles depended on orientation angle. Loss of soluble zinc from specimens varied with specimen size to the −0.2 power, even though Reynolds numbers based on average wind speeds and specimen length were well below those classically expected to produce turbulent flow.

Experiments were carried out in order to measure the collection efficiencies, E, with which small-sized water drops (of radii between 400 and 500 μm) carrying electrical charge, Q_a (from 5 × 10⁻¹⁴ to 2 × 10⁻¹¹ C), collect monodisperse aerosol particles of radii between 0.35 and 0.88 μm. The measured values of collection efficiency were within the range 1–6% and were in good agreement with previous results. The measurement show an increase in E with increase in aerosol particle radius, drop radius and drop charge.

A numerical integration scheme, designed for the gas-phase chemistry module in a 3D regional tropospheric chemistry model, is presented. Species in the chemical system are partitioned into “slow” and “fast” species, according to their lifetime under typical atmospheric conditions. A Newton-Raphson iterative scheme (implicit) is used for the fast species, while an explicit scheme is used for the slow ones. The hybrid implicit/explicit approach is tested against the Gear integration scheme for several rural and urban conditions (with and without emission/deposition). Comparisons with an exponential approximation scheme are also presented. The present integration scheme is shown to be accurate and efficient. With a 30 min integration step, the implicit/explicit scheme is at least 10-times faster than the Gear integration (with an equivalent integration step).

Methane measurements from weekly air samples collected at Tae-ahn Peninsula, Korea (TAP) present new constraints on the regional methane source strength of eastern Asia. Analysis of atmospheric trajectories shows that the lowest methane values observed at Tae-ahn are associated with southeasterly flow off the tropical Pacific Ocean and are similar to those observed at Cape Kumukahi, Hawaii. During June to August, northwesterly flow from the peat-rich wetlands located in the maritime provinces of the Far East former Soviet Union elevates methane at TAP by ∼80 ppb above the annual mean. Analysis of the Tae-ahn observations using a 3-D atmospheric methane model suggests that methane emission rates from the Far East Soviet wetlands may be ∼2 times those of Alaskan wetlands. Also, the relative maximum in May June at Tae-ahn constraints global CH₄ emissions from rice cultivation to ∼100 Tg yr⁻¹.

The influence of three different surface resistance formulations upon the resulting grid-averaged dry deposition velocity and the concentrations of O₃ and SO₂ calculated using the Acid Deposition and Oxidant Model (ADOM) has been investigated. Four ADOM simulations of the O₃ and SO₂ concentrations were compared with each other and the observations. The results show that two of the resistance formulations can decrease the original ADOM area-averaged dry deposition velocity by as much as 50% and increase the corresponding concentration by as much as 37% for O₃ and SO₂. However, all versions of the ADOM considerably underpredict the concentrations, implying weaknesses in ADOM that are not related to dry deposition. Wet surfaces appeared to have little influence on the estimated dry deposition velocity and concentration of O₃ but had a strong influence on those for SO₂.

Two chamber-based methods for measurement of emission of NO from soil have been compared. One method measured NO by conversion to NO₂ with a CrO₃ converter and NO₂ detection by luminol chemiluminescence. The other technique detects NO directly via NO/ozone chemiluminescence. The techniques were tested with a glass manifold system by addition of NO and other trace gases into a flowing zero air gas stream; water vapor was also added to the carrier gas in some cases. A second set of tests involved the simultaneous determination of NO concentrations from a chamber placed over the soil. Finally, flux measurements were made independently from common plots and from different plots within the same field. The luminol system was unaffected by the presence of ammonia, methylamine, acetonitrile and nitrous oxide, but had a lower response to NO in the presence of water vapor. The decrease was 7% at a relative humidity of 50%, and about 3% at a relative humidity of 23%. The NO/ozone chemiluminescence system was not influenced by any of the species doped into the gas stream. The simultaneous chamber data also showed a decreased response from the luminol system that was consistent with the humidity effect observed in the manifold tests. The average of independently measured flux values from common plots agreed reasonably well. However, the overall site mean flux determined by the luminol system was 74% of that of the NO/ozone system due to a larger data set from the luminol system. This comparison demonstrates that flux spatial heterogeneity can overwhelm analytical uncertainties, and that large sample sizes are needed to accurately characterize field fluxes.

This paper is concerned with theoretical aspects of the methodology of iceload measurements on an overhead line conductor (OHLC) of finite span and finite torsional stiffness. The purpose is to establish the relationships between the iceload on a fixed rod or sampler and the spatial average iceload on an OHLC. A theoretical database, generated using dynamical models for rime-ice accretion on conductors, is carefully analysed to express iceload data as a function of meteorological conditions and the mechanical properties of the OHLC. These results provide the required ratios of the iceload on a sampler to that on OHLCs as a function of time during an icing incident. A transfer function, relating theoretically predicted iceloads on an OHLC to that for a sampler, is then constructed and should prove useful in the development of the corresponding methodology for relating sets of field measurements in this way. For design purposes progress in the latter is desirable.