Atmospheric histories, growth rates and solubilities in seawater and other natural waters of the potential transient tracers HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116
Authors: Li Pingyang , Mühle Jens , Montzka Stephen A. , Oram David E. , Miller Benjamin R. , Weiss Ray F. , Fraser Paul J. , Tanhua Toste 
Published: January 2019

Abstract. We present consistent annual mean atmospheric histories
and growth rates for the mainly anthropogenic halogenated compounds HCFC-22,
HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116, which are all
potentially useful oceanic transient tracers (tracers of water transport
within the ocean), for the Northern and Southern Hemisphere with the aim of
providing input histories of these compounds for the equilibrium between the
atmosphere and surface ocean. We use observations of these halogenated
compounds made by the Advanced Global Atmospheric Gases Experiment (AGAGE),
the Scripps Institution of Oceanography (SIO), the Commonwealth Scientific
and Industrial Research Organization (CSIRO), the National Oceanic and
Atmospheric Administration (NOAA) and the University of East Anglia (UEA).
Prior to the direct observational record, we use archived air measurements,
firn air measurements and published model calculations to estimate the
atmospheric mole fraction histories. The results show that the atmospheric
mole fractions for each species, except HCFC-141b and HCFC-142b, have been
increasing since they were initially produced. Recently, the atmospheric
growth rates have been decreasing for the HCFCs (HCFC-22, HCFC-141b and
HCFC-142b), increasing for the HFCs (HFC-134a, HFC-125, HFC-23) and
stable with little fluctuation for the PFCs (PFC-14 and PFC-116) investigated
here. The atmospheric histories (source functions) and natural background
mole fractions show that HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125 and HFC-23
have the potential to be oceanic transient tracers for the next few decades
only because of the recently imposed bans on production and consumption.
When the atmospheric histories of the compounds are not monotonically
changing, the equilibrium atmospheric mole fraction (and ultimately the age
associated with that mole fraction) calculated from their concentration in
the ocean is not unique, reducing their potential as transient tracers.
Moreover, HFCs have potential to be oceanic transient tracers for a longer
period in the future than HCFCs as the growth rates of HFCs are increasing
and those of HCFCs are decreasing in the background atmosphere. PFC-14 and
PFC-116, however, have the potential to be tracers for longer periods
into the future due to their extremely long lifetimes, steady atmospheric
growth rates and no explicit ban on their emissions. In this work, we also
derive solubility functions for HCFC-22, HCFC-141b, HCFC-142b, HFC-134a,
HFC-125, HFC-23, PFC-14 and PFC-116 in water and seawater to facilitate
their use as oceanic transient tracers. These functions are based on the
Clark–Glew–Weiss (CGW) water solubility function fit and salting-out
coefficients estimated by the poly-parameter linear free-energy
relationships (pp-LFERs). Here we also provide three methods of seawater
solubility estimation for more compounds. Even though our intention is for
application in oceanic research, the work described in this paper is
potentially useful for tracer studies in a wide range of natural waters,
including freshwater and saline lakes, and, for the more stable compounds,
groundwaters.