A critical assessment of elemental mercury air/water exchange parameters

Simulating the vapour phase air/water exchange of p,p′-DDE, p,p′-DDT, lindane, and 2,3,7,8-tetrachlorodibenzodioxin

“…The nonisothermal Henry's Law constant is estimated by dividing the saturation atmospheric vapour concentration at temperature T atm: by the saturation aquatic vapour concentration at T aqu: . Loux (2004) concluded that this approximation is reasonable over a typical environmental temperature range of 0 to 40 C. The Henry's Law constants estimated in this work were obtained from vapour pressure and solubility estimation expressions published by Paasiverta et al (1999) and from estimates obtained from the SPARC computer model (Hilal et al, 2003a,b). When available, comparisons also were made with estimates derived from expressions published by Blanchard et al (2004).…”

“…From first principles (Mackay and Yeun, 1983;Schwarzenbach et al, 1993;Hoff et al, 1996;Cole and Caraco, 1998;Galarneau et al, 2000;Blanchard et al, 2004;Loux, 2004), one can anticipate mass transfer limited by molecular diffusion under these conditions. Hence, as suggested by Loux (2004), models yielding non-zero mass transfer coefficients at zero wind speed conditions are likely to be more accurate. Secondly, the issue of whether overall mass transfer coefficients are dependent on the Henry's Law constant is of considerable significance.…”

“…These three approaches in Table 1 include procedures developed by: Mackay and Yeun (1983), Hoff et al (1996) and Burns (2004). The five remaining procedures are empirical in nature, independent of the Henry's Law constant, and generally based on mass balance data obtained using sulfur hexafluoride as a model tracer gas: Cole and Caraco (1998), normalised Cole and Caraco (Loux, 2004), and Crusius and Wanninkhof models 1 -3 (2003). These relationships should be considered to be low to intermediate wind speed relationships; specifically, for very high wind speed marine systems one also might wish to consider the polynomial expressions developed by Wanninkhof (1992) and Wanninkhof and McGillis (1999) that, as will be demonstrated, may be suitable for compounds with larger Henry's Law constants.…”

“…In addition, the traditional Henry's Law constant is estimated under isothermal conditions (i.e., conditions where the atmospheric temperature equals the aqueous temperature). Because atmospheric and aquatic temperatures are rarely equal in environmental systems, Loux (2000Loux ( , 2001aLoux ( , and 2004 addressed the issue of the effects of atmosphericyaquatic temperature disequilibrium on Henry's Law constants and postulated the existence of a nonisothermal Henry's Law constant. The nonisothermal Henry's Law constant is estimated by dividing the saturation atmospheric vapour concentration at temperature T atm: by the saturation aquatic vapour concentration at T aqu: .…”

“…The five empirical models independent of the Henry's Law constant are generally derived from experimental datasets of rates of gaseous sulfur hexafluoride exchange in natural waters. As discussed in Loux (2004), a major source of uncertainty lies in relating these values of K 600 to gases with a different Schmidt number. Another issue arises in the area of whether overall mass transfer coefficients are dependent on the Henry's Law constant.…”