Jb. Johnson et al., THE INFLUENCE OF COMBUSTION-DERIVED POLLUTANTS ON LIMESTONE DETERIORATION .1. THE DRY DEPOSITION OF POLLUTANT GASES, Corrosion science, 38(1), 1996, pp. 105-131
This study concerns quantification of the relative chemical degradatio
n effects of dry deposition of combustion-derived atmospheric pollutan
ts, HCl, SO2 and NO2, on Portland and Monks Park limestones, employing
laboratory exposure chambers for periods of 30 days. Using presentati
on rates up to 40 x 10(-4) mu g cm(-2) s(-1), the pollutants were asse
ssed individually and in various combinations, along with ozone as oxi
dant, at 84% RH with dry or water-wetted surfaces. The degradation was
followed by analysis of exposed stone, for Cl-, SO42- and NO3-, and o
f run-off solution for Ca2+, in addition to the anions. From these dat
a, the total calcium released from limestone to reaction ions and prod
ucts and the percentages of each pollutant reacted (and so the deposit
ion velocity (V-D)) in each exposure regime were calculated. HCl acted
independently of the presence of other pollutants, showed 40 and 100%
reaction (mass transport control) and V-D values of 2.2 and 5.3 mm s(
-1), at 84% RH and on wetted surfaces, respectively. The reactivity of
SO2 rose from 2.5 to 35%, and V-D from 1 to 2.9 mm s(-1), from condit
ions of 84% RH to those with the presence of water, NO2 and O-3. Simil
arly, the reactivity of NO2 rose from 3 to 40% at 84% RH in the presen
ce of SO2 and O-3, with a V-D at 3 mm s(-1), but decreased in the pres
ence of run-off solution. A limited study was performed on smoke-coate
d and naturally exposed, reaction-product-coated, samples. In addition
to obvious factors such as deposited mass, chemical constitution and
transfer, smoke particle size distribution should also be considered i
n any possible action on limestone. Concerning naturally exposed sampl
es, non-wetted surface reaction products tended to reduce the attack o
f pollutants, but had no resisting effect when wetted.