Modeling of long-range transport on Taiwanʹs acid deposition under different weather conditions

The long-range and transboundary transport of acid deposition precursors in East Asia has become an important issue due to the industrial development in this area in recent years. To represent an entire yearʹs impact by long-range transport for Taiwanʹs acid deposition, six episodes in 1993 were selected for study using Taiwan Air Quality Model, which was developed on the basis of the Regional Acid Deposition Model system. The six episodes cover five types of weather conditions including the Northeasterly monsoon, Spring stationary front, Mei-Yu front, Summer shower, and Autumn front. Two emission conditions were simulated for each episode to quantify the long-range transport effect. One condition takes all emissions within the simulated domain into account as a base case, while another condition excludes Taiwanʹs emission and considers all of the other emissions as a control case. The results of the present study indicate that contributions of long-range transport to Taiwanʹs sulfur depositions range from 9 to 45% and nitrogen depositions from 6 to 33% for the six episodes. The most serious effect of long-range transport is the northeasterly monsoon episode for both total sulfur and total nitrogen deposition. The entire year contribution by long-range transport is estimated to be 39% for wet sulfate deposition, and 37% for wet nitrogen deposition for Taiwan.