Dry and wet deposition of elemental carbon on a tropical forest in Thailand

In order to further understand atmospheric deposition of elemental carbon (EC) with respect to climate and plant impacts, dry and wet deposition of EC was investigated in a tropical deciduous forest, Sakaerat, Thailand. Micro-meteorological measurements and monthly sampling of PM2.5 aerosols were carried out continuously over one year in 2010 at the top of an experimental tower 38 m above the ground established in the forest. The dry deposition was estimated by the inferential method by using an empirical parameterization of aerosol deposition velocity. For measurement of wet deposition, biweekly sampling of EC directly filtrated from rainwater was carried out continuously over one year in 2010. EC concentration significantly increased during the period from January to March due to heavy biomass burning, and decreased during the period from June to September due to less biomass burning and the washout effect by rainfall. High deposition velocities were caused by high wind speed in February to April and also by both large displacement height and medium wind speed in May to July. Dry deposition increased during the period from February to April when the concentration and deposition velocity were both high, and decreased during the period from June to December when the concentration or deposition velocity was low. Wet deposition peaked in March because of the washout effect of high EC in the atmosphere of the late dry season. Wet deposition was somewhat high from August to October with increased rainfall. Both dry and wet deposition increased in the leafless season and decreased in the leafy season, respectively. The annual dry and wet depositions were estimated as 0.58 and 0.05 mg m−2 day−1, respectively. Taking the uncertainties of estimations into account, dry deposition was still significantly higher than wet deposition.

► We characterized the dry and wet deposition of elemental carbon in a tropical forest. ► The majority of elemental carbon deposition is due to the dry disposition process. ► Both dry and wet depositions of elemental carbon are high in the leafless season.