Ammonium Variational Trends and the Ammonia Neutralization Effect on Acid Rain over East Asia

Abstract

The distribution and variations of ammonium and the ammonia neutralization effect on acid rain were examined in East Asia during the period of 2000 05 using observed wet deposition data from the Acid Deposition Monitoring Network in East Asia (EANET).Observational trends show a high proportion of NH 4 + in the total cations,with a six-year mean proportion of over 20% for continental and inland regions.The concentrations and deposition of NH 4 + were higher in western China and Vietnam than in other regions.The annual variations in NH 4 + concentration were smooth in most of the regions,except for southern China and Vietnam,where the NH 4 + concentrations increased,and western China,where the NH 4 + concentrations decreased.The neutralization factors (NFs) of NH 4 + indicate that ammonia has a great neutralization capability toward acid rain,including for the regions with low NH 4 + concentrations,such as Japan.The NFs were high in summer,with no obvious discrepancies between the northern and southern stations.However,the correlation coefficients between NH 4 + concentrations and rain pH values imply that the ammonia neutralization effects on the pH values were distinct only at southern China and southern Japan stations.The neutralization of precipitation by ammonia was estimated by comparing the discrepancies between the observed pH values and the pH values calculated without ammonia consuming the H + in NH 4 +.The results demonstrate that ammonia may increase annual mean pH values by 0.4 0.7 in southern China and by 0.15 0.25 in southern Japan.