Understanding nighttime methane signals at the Amazon Tall Tower Observatory (ATTO)

Abstract

Abstract. Methane (CH4) atmospheric mixing ratio measurements are analyzed for the period between June 2013 and November 2018 at the Amazon Tall Tower Observatory (ATTO). We describe the seasonal and diurnal patterns of nighttime events in which CH4 mixing ratios at the uppermost (79 m a.g.l.) inlet are significantly higher than the lowermost inlet (4 m a.g.l.) by 8 ppb or more. These nighttime events were found to be associated with a wind direction originating from the southeast and wind speeds between 2 and 5 m s−1. We found that these events happen under specific nighttime atmospheric conditions when compared to other nights, exhibiting less variable sensible heat flux, low net radiation and a strong thermal stratification above the canopy. Our analysis indicates that even at wind speeds of 5.8 m s−1 the turbulence intensity, given by the standard deviation of the vertical velocity, is suppressed to values lower than 0.3 m s−1. Given these findings, we suggest that these nighttime CH4 enhancements are advected from their source location by horizontal nonturbulent motions. The most likely source location is the Uatumã River, possibly influenced by dead stands of flooded forest trees that may be enhancing CH4 emissions from those areas. Finally, biomass burning and the Amazon River were discarded as potential CH4 sources.

Quantifying sources of Brazil's CH<sub>4</sub> emissions between 2010 and 2018 from satellite data

“…Measurements from ATTO (Andreae et al, 2015;Botía B. et al, 2020) were used for external validation of the inversion results. ATTO is located near Manaus within the Amazon rainforest.…”

“…Ganesan et al, 2019). Using both top-down and bottom-up methods together for national-scale greenhouse gas estimation is considered to be best practice (Calvo Buendia et al, 2019) and allows for the greatest process-level understanding of changes in the atmosphere.…”

The shadow of the Balbina dam: A synthesis of over 35 years of downstream impacts on floodplain forests in Central Amazonia

“…129 ± 14 × 10 9 g C) under almost constant anaerobic conditions (Resende et al, 2019) is likely to result in increasing GHG emissions, especially of CH 4 . The long-term monitoring of atmospheric CH 4 mixing ratios at the nearby ATTO site (Figure 1) by Botía et al (2020) detected night-time CH 4 increases, which most likely originated from the dead igapó forests; however, so far GHG emissions (CO 2 and CH 4 ) have only been measured in the Balbina reservoir, at the dam (turbine discharge and outflow), and in the first 30 km downstream of the power plant (Kemenes et al, 2011). To give the whole picture of GHG emission related to the Balbina dam, these measurements should be extended to the affected igapó floodplains in future studies and monitoring.…”

Total OH reactivity over the Amazon rainforest: variability with temperature, wind, rain, altitude, time of day, season, and an overall budget closure

“…For CO, 10 ppb and 30 ppb were subtracted from the 80 m values to derive lower limit mixing ratios for 150 m and 320 m, respectively. Methane values measured at 80 m were assumed to be valid for all heights, because the small height-related differences observed are not in an order of magnitude that affects OH reactivity (Botía et al, 2020).…”

“…Measurements of black carbon mass concentrations were obtained at the 325 m inlet of the ATTO tower using a multi-angle absorption photometer (MAAP, model 5012, Thermo Fisher Scientific, Waltham, USA), as described in Holanda et al (2020).…”