Dimethyl sulfide in the Amazon rain forest

Surface-to-atmosphere emissions of dimethyl sulfide (DMS) may impact global climate 44 through the formation of gaseous sulfuric acid, which can yield secondary sulfate 45 aerosols and contribute to new particle formation. While oceans are generally 46 considered the dominant source of DMS, a shortage of ecosystem observations prevents 47 an accurate analysis of terrestrial DMS sources. Using mass spectrometry, we quantified 48 ambient DMS mixing ratios within and above a primary rainforest ecosystem in the 49 central Amazon Basin in real-time (2010-2011) and at high vertical resolution (2013-50 2014). Elevated but highly variable DMS mixing ratios were observed within the 51 canopy, showing clear evidence of a net ecosystem source to the atmosphere during 52 both day and night in both the dry and wet seasons. Periods of high DMS mixing ratios 53 lasting up to 8 hours (up to 160 ppt) often occurred within the canopy and near the 54 surface during many evenings and nights. Daytime gradients showed mixing ratios (up 55 to 80 ppt) peaking near the top of the canopy as well as near the ground following a rain 56 event. The spatial and temporal distribution of DMS suggests that ambient levels and 57 their potentialmore » climatic impacts are dominated by local soil and plant emissions. A soil 58 source was confirmed by measurements of DMS emission fluxes from Amazon soils as 59 a function of temperature and soil moisture. Furthermore, light and temperature 60 dependent DMS emissions were measured from seven tropical tree species. Our study 61 has important implications for understanding terrestrial DMS sources and their role in 62 coupled land-atmosphere climate feedbacks. 63« less