Abstract. The Amazonian rainforest is a large tropical ecosystem, and is one of the last pristine continental terrains. This ecosystem is ideally located for the study of diel and seasonal behaviour of Biogenic Volatile Organic Compounds (BVOC) in the absence of local human interference. In this study, we report the first atmospheric BVOC measurements at the Amazonian Tall Tower Observatory (ATTO) site, located in Central Amazonia. A quadrupole Proton Transfer Reaction Mass Spectrometer (PTR-MS) with 7 ambient air inlets, positioned from near the ground to about 80 m (0.05, 0.5, 4, 24, 38, 53 and 79 m above the forest floor), was deployed for BVOC monitoring. We report diel and seasonal (February/March 2013 and September 2013) ambient mixing ratios for isoprene, monoterpenes, methyl vinyl ketone (MVK) + methacrolein (MACR), acetaldehyde, acetone, methyl ethyl ketone (MEK), methanol and acetonitrile. Clear diel and seasonal patterns were observed for all compounds during the study. In general, lower mixing ratios were observed during night, while maximum mixing ratios were observed with the peak in solar irradiation at 12:00 LT during the wet season (February/March 2013), and with the peak in temperature at 16:00 LT during the dry season (September 2013). Isoprene mixing ratios were highest within the canopy with a median of 7.6 ppb and interquartile range (IQR) of 6.1 ppb (dry season at 24 m, from 12:00–15:00). Monoterpene mixing ratios were higher than previously reported for any Amazonian rainforest ecosystem (median 1 ppb, IQR 0.38 ppb during the dry season at 24 m from 15:00–18:00). Oxygenated Volatile Organic Compound (OVOC) patterns indicated a transition from dominating forest emissions during the wet season to a blend of biogenic emission, photochemical production, and advection during the dry season. This was inferred from the high mixing ratios found within the canopy, and those obtained above the canopy for the wet and dry season, respectively. Our observations reveal strong seasonal BVOC patterns and oxidation capacity, reflected in the different vertical profiles obtained between the dry and wet season, most likely driven by insolation, temperature and phenology. In addition, significant differences to other reports of Amazonian BVOC demonstrate the need for long-term observations and more standardized measurement procedures in order to better understand the natural exchange of BVOC between the Amazonian rainforest and the atmosphere.
Improved land cover and emission factors for modeling biogenic volatile organic compounds emissions from Hong Kong
