This paper discusses the limitations of parametric modelling of corrosion and presents the case that accurate and exible models of atmospheric corrosion require an 'holistic' approach. In such an approach, the processes controlling corrosion across a wide range of physical scales are modelled. These models are based as much as possible on the processes controlling the phenomena under consideration. Being fundamentally based, these models can be extended outside the data sets from which they are derived. This is the rst of a series of papers outlining the use of this approach to predict corrosion in marine environments. It will consider the theoretical formulations required to model the production, transport and deposition of marine salts. It will present some predictions from these formulations and it will discuss the implications to corrosion of this theoretical understanding. Later papers will present the incorporation of these models into an information system and the validation of these models against data. CEST/2057 The authors are with CSIRO Manufacturing and Infrastructure Technologies,

This paper explores the simple principle that a metal surface wets when the surface relative humidity ͑RH͒ exceeds the deliquescent RH ͑DRH͒ of any salts on the surface. Data from field exposures across 19 sites in China, the Philippines, Indonesia, and Australia is used to determine the conditions under which openly exposed surfaces wet. At each site, surface temperature ͑of a zinc plate͒, ambient RH, sensor wetness, airborne salinity, and gaseous SO x and NO x were determined over a one-year period. In conjunction with these microclimate measures, the chemistry of airborne and deposited aerosols, as well as rainwater, were measured. Complimentary data from an environmental scanning electron microscope are presented in which salts derived from the evaporation of sea salt are rewetted. Using all of this data, an assessment of the probable contaminants controlling sensor wetting at each site is made. It is found that sites with similar International Standard Organization, ͑ISO͒ 9223, classifications in terms of industrial and marine airborne pollutants show similar surface contaminants and wetting characteristics. It is proposed that dominant contaminates can be identified for each ISO classification that are consistent with the general principle that wetting occurs when surface RH exceeds the DRH of the salts making up the contaminates. These salts can change from day to day due to the continual change in the composition of the contaminates and the ongoing homogenization of previously deposited salts through chemical reaction between salts and with the surface. Rain events usually clean the surface and start the cycle over again. The application of these findings to process models of corrosion is discussed, while generalized rules for predicting surface wetting based on climate data are proposed. It is found that these generalized rules predict total time of wetness to a high degree of accuracy.The concept of time of wetness ͑TOW͒ has been a very useful one for atmospheric corrosion scientists. 1 Indeed, the principle that corrosion can only occur in the presence of an electrolyte is based on fundamental electrochemical considerations. 2 Since the TOW concept was first proposed, sensors to measure TOW, 3-5 dose functions to define metallic corrosion 6-8 as a function of TOW, and degradation maps 9 based on these dose functions have been developed. However, the approximation commonly used to estimate TOW and included in International Standard Organization ͑ISO͒ 9225 ͓that TOW is the time when temperature is above 0°C and relative humidity ͑RH͒ is above 80%͔ cannot be directly derived from an understanding of the processes of surface wetting. Further studies of hygroscopic salts and aerosols indicate that salts, and thus the surfaces that they are on, may wet over a range of RH, depending on the deliquescent RH ͑DRH͒ of the salt. [10][11][12] In recent years, a number of authors have proposed refinements to the TOW concept in order to either derive better statistical fit with their corrosion data, or to account for...

This paper is the second in a series looking at understanding the factors controlling and predicting marine aerosol concentration on land. It looks at results from three transects across the Australian continent. In each transect, the airborne salinity was measured, using the wet candle method at distances from 10 m to 40 -300 km from the coast. The positions of the transects were selected to give a signi cant variation in the factors controlling salt production and transport. For example, one transect in South Australia was established where both high whitecap activity is likely to promote salt production and at terrain and prevailing winds are likely to favour transport. Another, in Queensland, was established where calm seas will limit salt production and very seasonal winds and high relative humidity and rainfall will limit transport. On the basis of this experimental study, the general validity of the fundamental concepts put forward in Part 1 is assessed. Further, the feasibility of building a mathematical model to predict salinity is determined and the main factors causing variations in salinity on land are outlined. The results are then used to assist in the interpretation of previous work in the literature. CEST/2058 The authors are with CSIRO Manufacturing and Infrastructure Technologies,

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