The collection of fog water is a simple and sustainable technology to obtain fresh water for afforestation, gardening, and as a drinking water source for human and animal consumption. In regions where fresh water is sparse and fog frequently occurs, it is feasible to set up a passive mesh system for fog water collection. The mesh is directly exposed to the atmosphere, and the foggy air is pushed through the mesh by the wind. Fog droplets are deposited on the mesh, combine to form larger droplets, and run down passing into a storage tank. Fog water collection rates vary dramatically from site to site but yearly averages from 3 to 10 l m -2 of mesh per day are typical of operational projects. The scope of this article is to review fog collection projects worldwide, to analyze factors of success, and to evaluate the prospects of this technology.
The dilution of jet engine exhaust in the plume behind cruising aircraft is determined from measured plume properties. The data set includes in situ measurements of CO2, NO, NOy, SO2, H2O1 temperature, and contrail diameters behind subsonic and supersonic aircraft in the upper troposphere and lower stratosphere, for plume ages of seconds to hours. The set of data is extended into the range of milliseconds based on computations and measured temperature values. The bulk plume dilution is expressed in terms of the dilution ratio N which is the mass of air with which the exhaust from a unit mass of burned fuel mixes. For: 0.006 s < t < 10 (exp 4) s, the bulk dilution ratio measured in more than 70 plume encounters follows approximately N = 7000 (t/t0) 0.8, t0 = 1 s
A land surface model including cloud (fog) water deposition on vegetation was developed to better predict the heat and water exchanges between the biosphere and atmosphere. A new scheme to calculate cloud water deposition on vegetation was implemented in this model. High performance of the model was confirmed by comparison of calculated heat and cloud water flux over a forest with measurements. The new model provided a better prediction of measured turbulent and gravitational fluxes of cloud water over the canopy than the commonly used cloud water deposition model. In addition, simple linear relationships between wind speed over the canopy ( | U | ) and deposition velocity of cloud water (V dep ) were found both in measurements and in the calculations. Numerical experiments using the model were performed to study the influences of two types of leaves (needle and broad leaves) and canopy structure parameters (total leaf area index and canopy height) on V dep . When the size of broad leaves is small, they can capture larger amounts of cloud water than needle leaves with the same canopy structure. The relationship between aerodynamic and canopy conductances for cloud water at a given total leaf area density (LAD) strongly influenced V dep . From this, it was found that trees whose LAD Ϸ 0.1 m 2 m Ϫ3 are the most efficient structures for cloud water deposition. A simple expression for the slope of V dep plotted against LAD obtained from the experiments can be useful for predicting total cloud water deposition to forests on large spatial scales.
Biomass-burning impacted air masses sampled over central and eastern Canada during the summer of 1990 as part of ABLE 3B contained enhanced mixing ratios of gaseous HNO3, HCOOH, CH3COOH, and what appears to be (COOH)2. These aircraft-based samples were collected from a variety of fresh burning plumes and more aged haze layers from different source regions. Values of the enhancement factor, delta X/delta CO, where X represents an acidic gas, for combustion-impacted air masses sampled both near and farther away from the fires, were relatively uniform. However, comparison of carboxylic acid emission ratios measured in laboratory fires to field plume enhancement factors indicates significant in-plume production of HCOOH. Biomass-burning appears to be an important source of HNO39 HCOOH, and CH3COOH to the troposphere over subarctic Canada
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