R. Sequeira et Mr. Peart, ANALYSIS OF THE PH OF DAILY RAINFALL AT A RURAL SITE IN HONG-KONG, 1989-1993, Science of the total environment, 159(2-3), 1995, pp. 177-183
Daily bulk precipitation samples have been collected and their pH meas
ured since April 1989 at a rural site, Kadoorie Agricultural Research
Centre (KARC), in the central New Territories, Hong Kong. The frequenc
y distribution of this population (N = 470) indicates a quasi-log norm
al distribution up until December, 1993. This is perhaps one of the lo
ngest daily pH-records available and it has climatological significanc
e for the future. The annual median and the running, volume-weighted p
H values (year end) are presented and they indicate collectively an an
nually oscillating pattern for which there is no obvious explanation a
t present. The annual volume-weighted pH values for 1990-1993 are 4.53
, 4.30, 5.04 and 4.32 and the corresponding running volume-weighted pH
values are 4.53, 4.39, 4.57 and 4.50. Most of the daily observations
indicate acidity on the Sorensen scale as expected, and there appears
to be no seasonal pattern to pH or amount of rainfall. Also, the volum
e of rainfall appears to exhibit no simple relationship with the acidi
ty of the rainfall. On the other hand, there is, apparently, an anthro
pogenic component of acid in Hong Kong if the increase in free hydroge
n ion concentration measured at the site is not entirely due to orogra
phic reduction of alkaline dust present at relatively lower elevations
in Hong Kong. Thus, there is some evidence that in contrast to the vo
lume-weighted pH in the mid-4's at Kadoorie, the pH of local backgroun
d rainfall in the territory of Hong Kong may be approximately 4.8, whi
le that of regional background (unpolluted) rainfall is probably brack
eted by pH approximately 5-5.5.