Cities are responsible for the largest anthropogenic CO2 emissions and are key to effective emission reduction strategies. Urban CO2 emissions estimated from vertical atmospheric measurements can ...contribute to an independent quantification of the reporting of national emissions and will thus have political implications. We analyzed vertical atmospheric CO2 mole fraction data obtained onboard commercial aircraft in proximity to 36 airports worldwide, as part of the Comprehensive Observation Network for Trace gases by Airliners (CONTRAIL) program. At many airports, we observed significant flight-to-flight variations of CO2 enhancements downwind of neighboring cities, providing advective fingerprints of city CO2 emissions. Observed CO2 variability increased with decreasing altitude, the magnitude of which varied from city to city. We found that the magnitude of CO2 variability near the ground (~1 km altitude) at an airport was correlated with the intensity of CO2 emissions from a nearby city. Our study has demonstrated the usefulness of commercial aircraft data for city-scale anthropogenic CO2 emission studies.
Inverse analysis was used to estimate fire carbon
emissions in Equatorial Asia induced by the big El Niño event in 2015.
This inverse analysis is unique because it extensively used high-precision
...atmospheric mole fraction data of carbon dioxide (CO2) from the
commercial aircraft observation project CONTRAIL. Through comparisons with
independent shipboard observations, especially carbon monoxide (CO) data,
the validity of the estimated fire-induced carbon emissions was demonstrated.
The best estimate, which used both aircraft and shipboard CO2
observations, indicated 273 Tg C for fire emissions from
September–October 2015. This 2-month period accounts for 75 % of the annual total fire emissions and 45 % of the annual total net carbon flux within the region, indicating that fire emissions are a dominant driving force of interannual variations of carbon fluxes in Equatorial Asia.
Several sensitivity experiments demonstrated that aircraft observations
could measure fire signals, though they showed a certain degree of
sensitivity to prior fire-emission data. The inversions coherently estimated
smaller fire emissions than the prior data, partially because of the small
contribution of peatland fires indicated by enhancement ratios of CO and
CO2 observed by the ship. In future warmer climate conditions,
Equatorial Asia may experience more severe droughts, which risks releasing a
large amount of carbon into the atmosphere. Therefore, the continuation of
aircraft and shipboard observations is fruitful for reliable monitoring of
carbon fluxes in Equatorial Asia.
A large number of in situ carbon dioxide (CO2) measurements from 5224 flights were taken by commercial airliners from 2005 to 2010. We analyzed the seasonal cycles in tropospheric CO2 in wide areas ...of the world over the Eurasian continent, the North Pacific, Southeast Asia, and Oceania. In the Northern Hemisphere, large seasonal changes of CO2 in the upper troposphere are found from spring through summer at northern midlatitudes to high latitudes with significant longitudinal differences; seasonally low CO2 mixing ratios are vertically transported from the surface over the Eurasian continent and then transported eastward to the North Pacific. In the Southern Hemisphere, the CO2 in the upper troposphere increases rapidly from April to June, indicating clearly the interhemispheric transport of high CO2 from the Northern Hemisphere winter. The rapid increase in the upper southern lower latitudes is equivalent to about 0.2 Pg increase in carbon. This interhemispheric transport should be adequately represented in general circulation models for source/sink estimates by inverse methods, because it is comparable to the seasonal or net fluxes estimated for a current inversion area size or a typical subcontinental domain. Estimation for transport of CO2 through the high altitudes will be more important than ever with increasing data from aircraft observations.
Key Points
A large number of in situ CO2 measurements are conducted by commercial aircraft
Seasonally low CO2 over Eurasia is transported to the North Pacific
CO2 in Southern Hemisphere increases rapidly from April by interhemispheric transport
Recent studies have shown the impact of expanding agricultural activities on atmospheric CO2 variations and the global carbon cycle. In this study, we show clear evidence of the measureable impact of ...Indian wintertime crops (mainly wheat) on the regional carbon budget using high‐frequency atmospheric CO2 measurements by Comprehensive Observation Network for Trace gases by Airliners (CONTRAIL) over Delhi; this phenomenon is not detected by the existing network of surface CO2 sites. While a general increase in the vertical profiles of CO2 toward the ground in the boundary layer was observed throughout December–April, we frequently observed sharp decreases below 2 km during January–March. Seasonal circulations during these 3 months indicated influences from neighboring croplands (with patchy urban areas) located upwind. We conclude that the observed CO2 decrease is attributable to active uptake by the crops grown in winter and that the uptake exceeds in magnitude the urban CO2 emissions from the Delhi metropolitan area.
Key Points
Commercial aircraft measurements showed increases/decreases of CO2 toward the ground over Delhi during December‐April
Substantial CO2 uptake by crops grown in winter was inferred
The wintertime crop CO2 uptake may exceed in magnitude the urban emissions from Delhi
Temporal variations of atmospheric radon-222 (222Rn) observed at four Japan Meteorological Agency stations in Japan by the Meteorological Research Institute were analyzed using an online Global ...Spectral Atmosphere Model-Transport Model (GSAM-TM). Monthly and diurnal variations and a series of synoptic high-222Rn events were extracted from 5 years to 12 years of 222Rn observations during 2007–2019. Observed seasonal patterns of winter maxima and summer minima, driven mainly by monsoons, were well reproduced by the GSAM-TM based on existing 222Rn emission inventories, but their absolute values were generally underestimated, indicating that our understanding of 222Rn emission processes in East Asia is lacking. The high-resolution model (∼ 60 km mesh) demonstrated that observed consecutive high-222Rn peaks at several-hour timescales were caused by two 222Rn streams from different regions and were not well resolved by the low-resolution model (∼ 200 km mesh). GSAM-TM simulations indicate that such cold-front-driven events are sometimes accompanied by complicated three-dimensional atmospheric structures such as stratospheric intrusion over the front, significantly affecting distributions of atmospheric components. A new calculation approach using hourly 222Rn values normalized to daily means was used to analyze the diurnal 222Rn cycle, allowing diurnal cycles in winter to be extracted from 222Rn data that are highly variable due to sporadic continental 222Rn outflows, which tend to obscure the diurnal variations. Normalized diurnal cycles of 222Rn in winter are consistent between observations and model simulations, and seem to be driven mainly by diurnal variations of planetary boundary layer height (PBLH). These results indicate that 222Rn in the near-surface atmosphere, transported from remote source regions, could vary diurnally by up to 10 % of the daily mean mainly owing to local PBLH variations, even without significant local 222Rn emissions.
Measurement of atmospheric carbon dioxide (CO2) is
indispensable for top-down estimation of surface CO2 sources/sinks by
an atmospheric transport model. Despite the growing importance of Asia in the
...global carbon budget, the region has only been sparsely monitored for atmospheric
CO2 and our understanding of atmospheric CO2
variations in the region (and thereby that of the regional carbon budget) is
still limited. In this study, we present climatological CO2
distributions over the Asia-Pacific region obtained from the CONTRAIL
(Comprehensive Observation Network for TRace gases by AIrLiner) measurements.
The high-frequency in-flight CO2 measurements over 10 years reveal a
clear seasonal variation in CO2 in the upper troposphere (UT), with a
maximum occurring in April–May and a minimum in August–September. The
CO2 mole fraction in the UT north of 40∘ N is low and highly
variable in June–August due to the arrival of air parcels with seasonally
low CO2 caused by the summertime biospheric uptake in boreal Eurasia.
For August–September in particular, the UT CO2 is noticeably low
within the Asian summer monsoon anticyclone associated with the convective
transport of strong biospheric CO2 uptake signal over South Asia.
During September as the anticyclone decays, a spreading of this low-CO2
area in the UT is observed in the vertical profiles of
CO2 over the Pacific Rim of continental East Asia. Simulation results
identify the influence of anthropogenic and biospheric CO2 fluxes in
the seasonal evolution of the spatial CO2 distribution over the
Asia-Pacific region. It is inferred that a substantial contribution to the UT
CO2 over the northwestern Pacific comes from continental East Asian
emissions in spring; but in the summer monsoon season, the prominent air mass
origin switches to South Asia and/or Southeast Asia with a distinct imprint
of the biospheric CO2 uptake. The CONTRAIL CO2 data provide
useful constraints to model estimates of surface fluxes and to the evaluation
of the satellite observations, in particular for the Asia-Pacific region.
Because very few measurements of atmospheric carbon dioxide (CO2) are available in the tropics, estimates of surface CO2 fluxes in tropical regions are beset with considerable uncertainties. To ...improve estimates of tropical terrestrial fluxes, atmospheric CO2 inversion was performed using passenger aircraft based measurements of the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project in addition to the surface measurement data set of GLOBALVIEW–CO2. Regional monthly fluxes at the earth's surface were estimated using the Bayesian synthesis approach focusing on the period 2006–2008 using the Nonhydrostatic Icosahedral Atmospheric Model‐based Transport Model (NICAM‐TM). By adding the aircraft to the surface data, the posterior flux errors were greatly reduced; specifically, error reductions of up to 64% were found for tropical Asia regions. This strong impact is closely related to efficient vertical transport in the tropics. The optimized surface fluxes using the CONTRAIL data were evaluated by comparing the simulated atmospheric CO2 distributions with independent aircraft measurements of the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) project. The inversion with the CONTRAIL data yields the global carbon sequestration rates of 2.22 ± 0.28 Pg C yr−1 for the terrestrial biosphere and 2.24 ± 0.27 Pg C yr−1 for the oceans (the both are adjusted by riverine input of CO2). For the first time the CONTRAIL CO2 measurements were used in an inversion system to identify the areas of greatest impact in terms of reducing flux uncertainties.
Key Points
Inversion of CO2 is conducted using passenger aircraft based measurements
Aircraft data greatly reduces flux uncertainties especially in the tropics
Inversion is evaluated by independent aircraft measurements
We present variations of CO2 in the tropopause region obtained by frequent in situ measurements aboard commercial aircraft. The data were obtained from a total of 373 flights between Japan and Europe ...during the period November 2005 to September 2007. The local phase and amplitude of the CO2 seasonal cycle varied with distance from the tropopause. In the upper troposphere and in the region just above the dynamical tropopause, a strong seasonal cycle with a springtime maximum and a relatively sharp minimum in July was observed. In the region bounded by potential temperatures 10 K to 30 K above the extratropical tropopause, no significant seasonal cycles were found. In the region greater than 30 K from the tropopause (i.e., at higher altitudes), sharp CO2 increases in summer followed by gradual decreases were found, resulting in a slightly increasing seasonal cycle amplitude with distance from the tropopause. The observed CO2 distributions also showed that CO2 isopleths followed the tropopause during the winter and spring, whereas in the summer they tracked potential temperature surfaces crossing the tropopause. The observed seasonal variation in CO2 suggests that the lowermost stratospheric region is influenced by a combination of (1) fast meridional transport of high CO2 from the tropical troposphere in the summer, (2) active subsidence of low CO2 from higher altitudes in the spring, and (3) relatively weak vertical mixing near the tropopause.
Background
In order to use in situ measurements to constrain urban anthropogenic emissions of carbon dioxide (CO
2
), we use a Lagrangian methodology based on diffusive backward trajectory tracer ...reconstructions and Bayesian inversion. The observations of atmospheric CO
2
were collected within the Tokyo Bay Area during the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) flights, from the Tsukuba tall tower of the Meteorological Research Institute (MRI) of the Japan Meteorological Agency and at two surface sites (Dodaira and Kisai) from the World Data Center for Greenhouse Gases (WDCGG).
Results
We produce gridded estimates of the CO
2
emissions and calculate the averages for different areas within the Kanto plain where Tokyo is located. Using these inversions as reference we investigate the impact of perturbing different elements in the inversion system. We modified the observations amount and location (surface only sparse vs. including aircraft CO
2
observations), the background representation, the wind data used to drive the transport model, the prior emissions magnitude and time resolution and error parameters of the inverse model.
Conclusions
Optimized fluxes were consistent with other estimates for the unperturbed simulations. Inclusion of CONTRAIL measurements resulted in significant differences in the magnitude of the retrieved fluxes, 13% on average for the whole domain and of up to 21% for the spatiotemporal cells with the highest fluxes. Changes in the background yielded differences in the retrieved fluxes of up to 50% and more. Simulated biases in the modelled transport cause differences in the retrieved fluxes of up to 30% similar to those obtained using different meteorological winds to advect the Lagrangian trajectories. Perturbations to the prior inventory can impact the fluxes by ~ 10% or more depending on the assumptions on the error covariances. All of these factors can cause significant differences in the estimated flux, and highlight the challenges in estimating regional CO
2
fluxes from atmospheric observations.
The seasonal variations of greenhouse gases at about 11 km altitude were analyzed from monthly air samples collected aboard a commercial airliner flying between Europe and Japan from April 2012 to ...March 2014. Compared to lower latitudes, the upper troposphere between 50 and 70°N showed higher CH4 and SF6 and an earlier seasonal phase of CO2. However, N2O values were similar to those in the subtropics. CH4, N2O, and SF6 in the lower stratosphere with potential temperature of up to 50 K above the tropopause showed seasonal variations with maxima in November/December and minima in April/May. At potential temperatures of 37.5–50 K above the tropopause, SF6 age was estimated to be about 22 months in May and 9 months in November. This strong seasonal variation is explained by the subsidence of high‐stratospheric air in spring and the effective flushing of the lowermost stratospheric air with tropospheric air in autumn.
Key Points
Higher CH4, SF6 at high latitudes in upper troposphere compared to subtropics
Larger seasonal CO2 changes at the high latitudes in the upper troposphere
Clear SF6 maximum in autumn in LS from tropospheric influences
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