The Amazon Basin plays key roles in the carbon and water cycles, climate change, atmospheric chemistry, and biodiversity. It has already been changed significantly by human activities, and more ...pervasive change is expected to occur in the coming decades. It is therefore essential to establish long-term measurement sites that provide a baseline record of present-day climatic, biogeochemical, and atmospheric conditions and that will be operated over coming decades to monitor change in the Amazon region, as human perturbations increase in the future. The Amazon Tall Tower Observatory (ATTO) has been set up in a pristine rain forest region in the central Amazon Basin, about 150 km northeast of the city of Manaus. Two 80 m towers have been operated at the site since 2012, and a 325 m tower is nearing completion in mid-2015. An ecological survey including a biodiversity assessment has been conducted in the forest region surrounding the site. Measurements of micrometeorological and atmospheric chemical variables were initiated in 2012, and their range has continued to broaden over the last few years. The meteorological and micrometeorological measurements include temperature and wind profiles, precipitation, water and energy fluxes, turbulence components, soil temperature profiles and soil heat fluxes, radiation fluxes, and visibility. A tree has been instrumented to measure stem profiles of temperature, light intensity, and water content in cryptogamic covers. The trace gas measurements comprise continuous monitoring of carbon dioxide, carbon monoxide, methane, and ozone at five to eight different heights, complemented by a variety of additional species measured during intensive campaigns (e.g., VOC, NO, NO2, and OH reactivity). Aerosol optical, microphysical, and chemical measurements are being made above the canopy as well as in the canopy space. They include aerosol light scattering and absorption, fluorescence, number and volume size distributions, chemical composition, cloud condensation nuclei (CCN) concentrations, and hygroscopicity. In this paper, we discuss the scientific context of the ATTO observatory and present an overview of results from ecological, meteorological, and chemical pilot studies at the ATTO site.
The hydroxyl radical (OH) removes most atmospheric pollutants from air. The loss frequency of OH radicals due to the combined effect of all gas-phase OH reactive species is a measureable quantity ...termed total OH reactivity. Here we present total OH reactivity observations in pristine Amazon rainforest air, as a function of season, time-of-day and height (0-80 m). Total OH reactivity is low during wet (10 s(-1)) and high during dry season (62 s(-1)). Comparison to individually measured trace gases reveals strong variation in unaccounted for OH reactivity, from 5 to 15% missing in wet-season afternoons to mostly unknown (average 79%) during dry season. During dry-season afternoons isoprene, considered the dominant reagent with OH in rainforests, only accounts for ∼20% of the total OH reactivity. Vertical profiles of OH reactivity are shaped by biogenic emissions, photochemistry and turbulent mixing. The rainforest floor was identified as a significant but poorly characterized source of OH reactivity.
Eastern Boundary Upwelling Systems (EBUSs) are coastal hotspots of the potent greenhouse gas nitrous oxide (N2O). However, estimates of their emissions suffer from large uncertainties due to their ...significant spatial and temporal heterogeneity. Here, we derive the first multiyear, monthly resolution N2O emissions from three of the four major EBUSs using high‐frequency coastal atmospheric measurements and an inverse method. We find average combined N2O emissions from the northern California, Benguela, and southern Canary upwelling systems to be 57.7 (51.4–63.9) Gg‐N yr−1. We also find an offshore region near the Benguela EBUS that exhibits large pulses of emissions with emissions that reach 677 Gg‐N yr−1 in 1 month. Our findings highlight that atmospheric measurements coupled with inverse modeling can capture the large variability in EBUS emissions by quantifying emissions over large spatial distances and over long time periods compared to previous methods using traditional oceanographic measurements.
Plain Language Summary
Eastern Boundary Upwelling Systems (EBUSs) are important emissions hotspots of marine nitrous oxide to the atmosphere, where it acts as a greenhouse gas and ozone depleting substance. Emissions from the EBUSs are highly episodic, and most previous estimates are snapshots derived from ship‐based measurements. The variability in emissions combined with the sparsity of measurements makes EBUS emission estimates highly uncertain. Here, we use multiyear, near‐continuous atmospheric measurements from coastal stations and an inverse modeling framework to derive emissions from three of the four major EBUSs. Our results quantify the significant spatial and temporal variability in emissions, which is not well‐represented in global studies of marine nitrous oxide emissions.
Key Points
Eastern Boundary Upwelling System (EBUS) N2O emissions are episodic, and methods are needed to capture their variability in space and time
Previous upscaled estimates of EBUS emissions based on sparse measurements may be inaccurate
N2O emissions from the northern California upwelling system vary with PDO phase
We present methane (CH4) flux estimates for 2005 to 2013 from a Bayesian inversion focusing on the high northern latitudes (north of 50° N). Our inversion is based on atmospheric transport modelled ...by the Lagrangian particle dispersion model FLEXPART and CH4 observations from 17 in situ and five discrete flask-sampling sites distributed over northern North America and Eurasia. CH4 fluxes are determined at monthly temporal resolution and on a variable grid with maximum resolution of 1° × 1°. Our inversion finds a CH4 source from the high northern latitudes of 82 to 84 Tg yr−1, constituting ∼ 15 % of the global total, compared to 64 to 68 Tg yr−1 (∼ 12 %) in the prior estimates. For northern North America, we estimate a mean source of 16.6 to 17.9 Tg yr−1, which is dominated by fluxes in the Hudson Bay Lowlands (HBL) and western Canada, specifically the province of Alberta. Our estimate for the HBL, of 2.7 to 3.4 Tg yr−1, is close to the prior estimate (which includes wetland fluxes from the land surface model, LPX-Bern) and to other independent inversion estimates. However, our estimate for Alberta, of 5.0 to 5.8 Tg yr−1, is significantly higher than the prior (which also includes anthropogenic sources from the EDGAR-4.2FT2010 inventory). Since the fluxes from this region persist throughout the winter, this may signify that the anthropogenic emissions are underestimated. For northern Eurasia, we find a mean source of 52.2 to 55.5 Tg yr−1, with a strong contribution from fluxes in the Western Siberian Lowlands (WSL) for which we estimate a source of 19.3 to 19.9 Tg yr−1. Over the 9-year inversion period, we find significant year-to-year variations in the fluxes, which in North America, and specifically in the HBL, appear to be driven at least in part by soil temperature, while in the WSL, the variability is more dependent on soil moisture. Moreover, we find significant positive trends in the CH4 fluxes in North America of 0.38 to 0.57 Tg yr−2, and northern Eurasia of 0.76 to 1.09 Tg yr−2. In North America, this could be due to an increase in soil temperature, while in North Eurasia, specifically Russia, the trend is likely due, at least in part, to an increase in anthropogenic sources.
During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO
2
) ...exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO
2
seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO
2
gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO
2
cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO
2
due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO
2
transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO
2
uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO
2
anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO
2
anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018.
This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
The tropical forests are Earth's largest source of
biogenic volatile organic compounds (BVOCs) and thus also the largest
atmospheric sink region for the hydroxyl radical (OH). However, the OH sink
...above tropical forests is poorly understood, as past studies have revealed large
unattributed fractions of total OH reactivity. We present the first total OH
reactivity and volatile organic compound (VOC) measurements made at the Amazon Tall Tower Observatory
(ATTO) at 80, 150, and 320 m above ground level, covering two dry seasons,
one wet season, and one transition season in 2018–2019. By considering a wide range
of previously unaccounted for VOCs, which we identified by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), the
unattributed fraction was with an overall average of 19 % within the
measurement uncertainty of ∼ 35 %. In terms of seasonal
average OH reactivity, isoprene accounted for 23 %–43 % of the total and oxygenated VOCs (OVOCs) for 22 %–40 %, while monoterpenes, sesquiterpenes,
and green leaf volatiles combined were responsible for 9 %–14 %. These
findings show that OVOCs were until now an underestimated contributor to the
OH sink above the Amazon forest. By day, total OH reactivity decreased towards higher altitudes with
strongest vertical gradients observed around noon during the dry season
(−0.026 s−1 m−1), while the gradient was inverted at night.
Seasonal differences in total OH reactivity were observed, with the lowest
daytime average and standard deviation of 19.9 ± 6.2 s−1 during
a wet–dry transition season with frequent precipitation; 23.7 ± 6.5 s−1 during the wet season; and the highest average OH reactivities
during two dry-season observation periods with 28.1 ± 7.9 s−1
and 29.1 ± 10.8 s−1, respectively. The effects of different
environmental parameters on the OH sink were investigated, and quantified,
where possible. Precipitation caused short-term spikes in total OH
reactivity, which were followed by below-normal OH reactivity for several
hours. Biomass burning increased total OH reactivity by 2.7 to
9.5 s−1. We present a temperature-dependent parameterization of OH
reactivity that could be applied in future models of the OH sink to further
reduce our knowledge gaps in tropical-forest OH chemistry.
The Total Carbon Column Observing Network (TCCON) is a ground-based network of Fourier Transform Spectrometer (FTS) sites around the globe, where the column abundances of CO2 , CH4 , N2 O, CO and O2 ...are measured. CO2 is constrained with a precision better than 0.25% (1-σ). To achieve a similarly high accuracy, calibration to World Meteorological Organization (WMO) standards is required. This paper introduces the first aircraft calibration campaign of five European TCCON sites and a mobile FTS instrument. A series of WMO standards in-situ profiles were obtained over European TCCON sites via aircraft and compared with retrievals of CO2 column amounts from the TCCON instruments. The results of the campaign show that the FTS measurements are consistently biased 1.1% ± 0.2% low with respect to WMO standards, in agreement with previous TCCON calibration campaigns. The standard a priori profile for the TCCON FTS retrievals is shown to not add a bias. The same calibration factor is generated using aircraft profiles as a priori and with the TCCON standard a priori. With a calibration to WMO standards, the highly precise TCCON CO2 measurements of total column concentrations provide a suitable database for the calibration and validation of nadir-viewing satellites.
The recent development and improvement of commercial laser-based
spectrometers have expanded in situ continuous observations of water vapour
(H2O) stable isotope compositions (e.g. δ18O and δ2H) in a ...variety of sites worldwide. However, we still lack
continuous observations in the Amazon, a region that significantly
influences atmospheric and hydrological cycles on local to global scales. In
order to achieve accurate on-site observations, commercial water isotope
analysers require regular in situ calibration, which includes the correction
of H2O concentration dependence (H2O dependence) of isotopic
measurements. Past studies have assessed the H2O dependence for air
with H2O concentrations of up to 35 000 ppm, a value that is frequently
surpassed in tropical rainforest settings like the central Amazon where we
plan continuous observations. Here we investigated the performance of two
commercial analysers (L1102i and L2130i models, Picarro, Inc., USA) for
measuring δ18O and δ2H in atmospheric moisture at
four different H2O levels from 21 500 to 41 000 ppm. These H2O
levels were created by a custom-built calibration unit designed for regular
in situ calibration. Measurements on the newer analyser model (L2130i) had
better precision for δ18O and δ2H and demonstrated
less influence of H2O concentration on the measurement accuracy at each
concentration level compared to the older L1102i. Based on our findings, we
identified the most appropriate calibration strategy for
H2O dependence, adapted to our calibration system. The best strategy
required conducting a two-point calibration with four different H2O
concentration levels, carried out at the beginning and end of the
calibration interval. The smallest uncertainties in calibrating
H2O dependence of isotopic accuracy of the two analysers were
achieved using a linear surface fitting method and a 28 h calibration
interval, except for the δ18O accuracy of the L1102i analyser
for which the cubic fitting method gave the best results. The uncertainties in
H2O dependence calibration did not show any significant difference
using calibration intervals from 28 up to 196 h; this suggested that one
H2O dependence calibration per week for the L2130i and L1102i
analysers is sufficient. This study shows that the cavity ring-down spectroscopy (CRDS) analysers,
appropriately calibrated for H2O dependence, allow the detection of
natural signals of stable water vapour isotopes at very high humidity
levels, which has promising implications for water cycle studies in areas
like the central Amazon rainforest and other tropical regions.
We use a global chemical transport model (GEOS-Chem) to interpret observed light-absorbing aerosols in Amazonia during the wet season. Observed aerosol properties, including black carbon (BC) ...concentration and light absorption, at the Amazon Tall Tower Observatory (ATTO) site in the central Amazon have relatively low background levels but frequently show high peaks during the study period of January–April 2014. With daily temporal resolution for open fire emissions and modified aerosol optical properties, our model successfully captures the observed variation in fine/coarse aerosol and BC concentrations as well as aerosol light absorption and its wavelength dependence over the Amazon Basin. The source attribution in the model indicates the important influence of open fire on the observed variances of aerosol concentrations and absorption, mainly from regional sources (northern South America) and from northern Africa. The contribution of open fires from these two regions is comparable, with the latter becoming more important in the late wet season. The analysis of correlation and enhancement ratios of BC versus CO suggests transport times of < 3 days for regional fires and ∼ 11 days for African plumes arriving at ATTO during the wet season. The model performance of long-range transport of African plumes is also evaluated with observations from AERONET, MODIS, and CALIOP. Simulated absorption aerosol optical depth (AAOD) averaged over the wet season is lower than 0.0015 over the central Amazon, including the ATTO site. We find that more than 50 % of total absorption at 550 nm is from BC, except for the northeastern Amazon and the Guianas, where the influence of dust becomes significant (up to 35 %). The brown carbon contribution is generally between 20 and 30 %. The distribution of absorption Ångström exponents (AAE) suggests more influence from fossil fuel combustion in the southern part of the basin (AAE ∼ 1) but more open fire and dust influence in the northern part (AAE > 1.8). Uncertainty analysis shows that accounting for absorption due to secondary organic aerosol (SOA) and primary biogenic aerosol (PBA) particles could result in differences of < 8 and 5–40 % in total absorption, respectively.
Coastal zones are important source regions for a variety of trace gases, including halocarbons and sulfur-bearing species. While salt marshes, macroalgae and phytoplankton communities have been ...intensively studied, little is known about trace gas fluxes in seagrass meadows. Here we report results of a newly developed dynamic flux chamber system that can be deployed in intertidal areas over full tidal cycles allowing for highly time-resolved measurements. The fluxes of CO2, methane (CH4) and a range of volatile organic compounds (VOCs) showed a complex dynamic mediated by tide and light. In contrast to most previous studies, our data indicate significantly enhanced fluxes during tidal immersion relative to periods of air exposure. Short emission peaks occurred with onset of the feeder current at the sampling site. We suggest an overall strong effect of advective transport processes to explain the elevated fluxes during tidal immersion. Many emission estimates from tidally influenced coastal areas still rely on measurements carried out during low tide only. Hence, our results may have significant implications for budgeting trace gases in coastal areas. This dynamic flux chamber system provides intensive time series data of community respiration (at night) and net community production (during the day) of shallow coastal systems.
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