Analysis of ion composition from airborne particulate deposition on Jambolan plum tree (Syzygium cumini) was carried out from July 2012 – March 2013.  In wet season (July 2012 – October 2012) samples were collected once a month, while in dry season (November 2012 – March 2013) samples were collected every 10 days. The study site is categorized as sub-urban area and located at Mae Hia Research Center, Chiang Mai University, Chiang Mai, Thailand. This study aims to test and apply leaf-washing method to collect particulate samples deposited on tree leaves and to analyze dry deposition of ions bounded with particulates for assessment of air contaminants and their possible sources. Leaf-washing method is simple, low cost, no power or maintenance requirement and can be applied in wider area. Deionized water was used for individual leaf washing and collected in a plastic bottle. Samples were then measured for pH and electro-conductivity. The filtered samples were analyzed for major cations (Ca²⁺, NH₄⁺, Na⁺, K⁺ and Mg²⁺)  and anions (Cl^-, SO₄^2- and NO₃^-) by Ion Chromatograph. Dry deposition (mg/m²) of ions in descending order were Ca²⁺ (28.1 mg/m²) > SO₄^2- (5.35 mg/m²) > NO₃^- (4.71 mg/m²) > K⁺ (2.82 mg/m²) > Cl^- (2.13 mg/m²) > Na⁺ (1.70 mg/m²) > Mg²⁺ (1.04 mg/m²) > NH₄⁺ (0.93 mg/m²). Ca²⁺ was found to be a major component (~ 60 % of total ions). Its main contribution is from soil resuspension. The ranking of ion deposition in wet and dry seasons showed the similar trends. However, the depositions in dry season were ~ 2 - 3 times higher than those in wet season due to wash out effect by rain. Correlation between the ions such as SO₄^2- & NO₃^- (r = 0.601) and Ca²⁺ & Mg²⁺ (r = 0.771) were relatively high indicating their origin from similar sources.

 Keywords: Dry deposition, Ion composition, Air pollution, Leaf-washing method