scholarly journals Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland

2011 ◽  
Vol 11 (5) ◽  
pp. 15975-16021 ◽  
Author(s):  
C. Buizert ◽  
P. Martinerie ◽  
V. V. Petrenko ◽  
J. P. Severinghaus ◽  
C. M. Trudinger ◽  
...  
Keyword(s):  
Ice Core ◽  
Effective Diffusivity ◽  
Air Transport ◽  
Ice Age ◽  
Atmospheric Composition ◽  
Advective Transport ◽  
Mixing Ratios ◽  
The Difference ◽  
Model Tuning ◽  
Intercomparison Study

Abstract. Compacted snow (firn) preserves a continuous record of atmospheric composition up to a century back in time. Firn air transport modeling is essential for interpretation of firn gas records. Each site needs to be characterised individually through a tuning procedure, in which the effective diffusivity at each depth is adjusted to optimise the agreement between modeled and measured mixing ratios of a selected reference gas (usually CO2). We present the characterisation of the NEEM site, Northern Greenland (77.45° N 51.06° W), where an ensemble of ten reference tracers is used to constrain the diffusivity reconstruction. By analysing uncertainties in both data and the reference gas atmospheric histories, we can objectively assign weights to each of the gases used for the model tuning, and define a root mean square criterion that is minimised in the tuning. Each tracer constrains the firn profile differently through its unique atmospheric history and free air diffusivity, making our multiple-tracer characterisation method a clear improvement over the commonly used single-tracer tuning. Six firn air transport models are tuned to the NEEM site; all models successfully reproduce the data within a 1σ Gaussian distribution. The modern day Δage, i.e. the difference between gas age and ice age, is calculated to be 182 ± 8 yr. We find evidence that diffusivity does not vanish completely in the firn lock-in zone, as is commonly assumed. We further present the first intercomparison study of firn air models, where we introduce diagnostic scenarios designed to probe specific aspects of the model physics. Our results show that there are major differences in the way the models handle advective transport. Furthermore diffusive fractionation of isotopes in the firn is poorly constrained by the models, which has consequences for attempts to reconstruct the isotopic composition of trace gases back in time using firn air and ice core records.

scholarly journals Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland

2012 ◽  
Vol 12 (9) ◽  
pp. 4259-4277 ◽  
Author(s):  
C. Buizert ◽  
P. Martinerie ◽  
V. V. Petrenko ◽  
J. P. Severinghaus ◽  
C. M. Trudinger ◽  
...  
Keyword(s):  
Ice Core ◽  
Air Transport ◽  
Ice Age ◽  
Age Difference ◽  
Advective Transport ◽  
Transport Models ◽  
Free Air ◽  
Model Tuning ◽  
Intercomparison Study ◽  
Lock In

Abstract. Air was sampled from the porous firn layer at the NEEM site in Northern Greenland. We use an ensemble of ten reference tracers of known atmospheric history to characterise the transport properties of the site. By analysing uncertainties in both data and the reference gas atmospheric histories, we can objectively assign weights to each of the gases used for the depth-diffusivity reconstruction. We define an objective root mean square criterion that is minimised in the model tuning procedure. Each tracer constrains the firn profile differently through its unique atmospheric history and free air diffusivity, making our multiple-tracer characterisation method a clear improvement over the commonly used single-tracer tuning. Six firn air transport models are tuned to the NEEM site; all models successfully reproduce the data within a 1σ Gaussian distribution. A comparison between two replicate boreholes drilled 64 m apart shows differences in measured mixing ratio profiles that exceed the experimental error. We find evidence that diffusivity does not vanish completely in the lock-in zone, as is commonly assumed. The ice age- gas age difference (Δage) at the firn-ice transition is calculated to be 182+3−9 yr. We further present the first intercomparison study of firn air models, where we introduce diagnostic scenarios designed to probe specific aspects of the model physics. Our results show that there are major differences in the way the models handle advective transport. Furthermore, diffusive fractionation of isotopes in the firn is poorly constrained by the models, which has consequences for attempts to reconstruct the isotopic composition of trace gases back in time using firn air and ice core records.

scholarly journals Comparison of surface ozone simulation among selected regional models in MICS-Asia III – effects of chemistry and vertical transport for the causes of difference

2019 ◽  
Vol 19 (1) ◽  
pp. 603-615 ◽  
Author(s):  
Hajime Akimoto ◽  
Tatsuya Nagashima ◽  
Jie Li ◽  
Joshua S. Fu ◽  
Dongsheng Ji ◽  
...  
Keyword(s):  
Surface Ozone ◽  
Early Morning ◽  
Photochemical Activity ◽  
Vertical Transport ◽  
Ozone Production ◽  
Phase Iii ◽  
Regional Models ◽  
Mixing Ratios ◽  
The Difference ◽  
Intercomparison Study

Abstract. In order to clarify the causes of variability among the model outputs for surface ozone in the Model Intercomparison Study Asia Phase III (MICS-Asia III), three regional models, CMAQ v.5.0.2, CMAQ v.4.7.1, and NAQPMS (abbreviated as NAQM in this paper), have been selected. Detailed analyses of monthly averaged diurnal variation have been performed for selected grids covering the metropolitan areas of Beijing and Tokyo and at a remote oceanic site, Oki. The chemical reaction mechanism, SAPRC99, used in the CMAQ models tended to give a higher net chemical ozone production than CBM-Z used in NAQM, agreeing with previous studies. Inclusion of the heterogeneous “renoxification” reaction of HNO3 (on soot surface)→NO+NO2 only in NAQM would give a higher NO concentration resulting in a better agreement with observational data for NO and nighttime O3 mixing ratios. In addition to chemical processes, the difference in the vertical transport of O3 was found to affect the simulated results significantly. Particularly, the increase in downward O3 flux from the upper layer to the surface after dawn was found to be substantially different among the models. Larger early morning vertical transport of O3 simulated by CMAQ 5.0.2 is thought to be the reason for higher daytime O3 in July in this model. All three models overestimated the daytime ozone by ca. 20 ppbv at the remote site Oki in July, where in situ photochemical activity is minimal.

scholarly journals The influence of layering and barometric pumping on firn air transport in a 2-D model

2018 ◽  
Vol 12 (6) ◽  
pp. 2021-2037 ◽  
Author(s):  
Benjamin Birner ◽  
Christo Buizert ◽  
Till J. W. Wagner ◽  
Jeffrey P. Severinghaus
Keyword(s):  
Dispersion Model ◽  
Noble Gas ◽  
Ice Core ◽  
Transport Processes ◽  
Air Transport ◽  
Atmospheric Composition ◽  
Elemental Ratios ◽  
Barometric Pumping ◽  
Kinetic Fractionation ◽  
D Model

Abstract. Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. However, the influence of low-permeability layers and barometric pumping (driven by surface pressure variability) on firn air transport is not well understood and is not readily captured in conventional one-dimensional (1-D) firn air models. Here we present a two-dimensional (2-D) trace gas advection–diffusion–dispersion model that accounts for discontinuous horizontal layers of reduced permeability. We find that layering or barometric pumping individually yields too small a reduction in gravitational settling to match observations. In contrast, when both effects are active, the model's gravitational fractionation is suppressed as observed. Layering focuses airflows in certain regions in the 2-D model, which acts to amplify the dispersive mixing resulting from barometric pumping. Hence, the representation of both factors is needed to obtain a realistic emergence of the lock-in zone. In contrast to expectations, we find that the addition of barometric pumping in the layered 2-D model does not substantially change the differential kinetic fractionation of fast- and slow-diffusing trace gases. Like 1-D models, the 2-D model substantially underestimates the amount of differential kinetic fractionation seen in actual observations, suggesting that further subgrid-scale processes may be missing in the current generation of firn air transport models. However, we find robust scaling relationships between kinetic isotope fractionation of different noble gas isotope and elemental ratios. These relationships may be used to correct for kinetic fractionation in future high-precision ice core studies and can amount to a bias of up to 0.45 °C in noble-gas-based mean ocean temperature reconstructions at WAIS Divide, Antarctica.

scholarly journals Comparison of Surface Ozone Simulation among Selected Regional Models in MICS-Asia III – Effect of Chemistry and Vertical Transport for the Causes of Difference –

2018 ◽  
Author(s):  
Hajime Akimoto ◽  
Tatsuya Nagashima ◽  
Jie Li ◽  
Joshua Fu ◽  
Dongsheng Ji ◽  
...  
Keyword(s):  
Surface Ozone ◽  
Early Morning ◽  
Photochemical Activity ◽  
Vertical Transport ◽  
Ozone Production ◽  
Phase Iii ◽  
Regional Models ◽  
Mixing Ratios ◽  
The Difference ◽  
Intercomparison Study

Abstract. In order to clarify the cause of variability among the model outputs for surface ozone in the Model Intercomparison Study Asia Phase III (MICS-Asia III), three regional models, CMAQ v.5.0.2, CMAQ v.4.7.1 and NAQPMS (abbreviated as NAQM in this paper) have been selected. The detailed analyses have been made for monthly averaged diurnal variation for select grids covering metropolitan area of Beijing and Tokyo, and at a remote oceanic site, Oki. The chemical reaction mechanism, SAPRC99 used in the CMAQ models tends to give higher net chemical ozone production than CBM-Z used in NAQM agreeing with previous studies. Inclusion of heterogeneous “renoxification” reaction of HNO3 (on soot) → NO + NO2 only in NAQM is supposed to give higher NO concentration to give better agreement with observational data for NO and nighttime O3 mixing ratios. In addition to chemistry, the difference in vertical transport of O3 was found to affect the simulated results significantly. Particularly, the increase in downward flux of O3 from upper layer to the surface after the dawn is found to be substantially different among the models. Larger early morning vertical transport of O3 by CMAQ 5.0.2 would be the reason for higher daytime O3 by this model in July. All the three models overestimate the daytime ozone by ca. 20 ppbv at the remote site Oki in July, where in situ photochemical activity is minimal.

scholarly journals The influence of layering and barometric pumping on firn air transport in a 2D model

2017 ◽  
Author(s):  
Benjamin Birner ◽  
Christo Buizert ◽  
Till J. W. Wagner ◽  
Jeffrey P. Severinghaus
Keyword(s):  
Dispersion Model ◽  
Noble Gas ◽  
Ice Core ◽  
Transport Processes ◽  
Air Transport ◽  
Atmospheric Composition ◽  
Elemental Ratios ◽  
Barometric Pumping ◽  
Kinetic Fractionation ◽  
2D Model

Abstract. Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. However, the influence of impermeable layers and barometric pumping (driven by surface pressure variability) on firn air transport is not well understood and cannot be captured in conventional 1-dimensional firn air models. Here we present a 2-dimensional (2D) trace gas advection-diffusion-dispersion model that accounts for discontinuous horizontal layers of reduced permeability. We find that layering and barometric pumping individually yield too small a reduction in gravitational settling to match observations. In contrast, a combination of both effects more strongly suppresses gravitational fractionation. Layering locally focuses airflows in the 2D model and thus amplifies the dispersive mixing resulting from barometric pumping. Hence, the representation of both factors is needed to obtain a more natural emergence of the lock-in zone. Moreover, we find that barometric pumping in the layered 2D model does not substantially change the differential kinetic fractionation of fast and slow diffusing trace gases, which is observed in nature. This suggests that further subgrid-scale physics may be missing in the current generation of firn air transport models. However, we find robust scaling relationships between kinetic isotope fractionation of different noble gas isotope and elemental ratios. These relationships may be used to correct for kinetic fractionation in future high precision ice core studies.

scholarly journals Analytical constraints on layered gas trapping and smoothing of atmospheric variability in ice under low-accumulation conditions

2017 ◽  
Vol 13 (12) ◽  
pp. 1815-1830 ◽  
Author(s):  
Kévin Fourteau ◽  
Xavier Faïn ◽  
Patricia Martinerie ◽  
Amaëlle Landais ◽  
Alexey A. Ekaykin ◽  
...  
Keyword(s):  
Ice Core ◽  
Flow Analysis ◽  
Atmospheric Composition ◽  
Atmospheric Variability ◽  
High Accumulation ◽  
Antarctic Plateau ◽  
Mixing Ratios ◽  
Gas Trapping ◽  
Continuous Flow Analysis ◽  
Concentration Changes

Abstract. We investigate for the first time the loss and alteration of past atmospheric information from air trapping mechanisms under low-accumulation conditions through continuous CH4 (and CO) measurements. Methane concentration changes were measured over the Dansgaard–Oeschger event 17 (DO-17,  ∼  60 000 yr BP) in the Antarctic Vostok 4G-2 ice core. Measurements were performed using continuous-flow analysis combined with laser spectroscopy. The results highlight many anomalous layers at the centimeter scale that are unevenly distributed along the ice core. The anomalous methane mixing ratios differ from those in the immediate surrounding layers by up to 50 ppbv. This phenomenon can be theoretically reproduced by a simple layered trapping model, creating very localized gas age scale inversions. We propose a method for cleaning the record of anomalous values that aims at minimizing the bias in the overall signal. Once the layered-trapping-induced anomalies are removed from the record, DO-17 appears to be smoother than its equivalent record from the high-accumulation WAIS Divide ice core. This is expected due to the slower sinking and densification speeds of firn layers at lower accumulation. However, the degree of smoothing appears surprisingly similar between modern and DO-17 conditions at Vostok. This suggests that glacial records of trace gases from low-accumulation sites in the East Antarctic plateau can provide a better time resolution of past atmospheric composition changes than previously expected. We also developed a numerical method to extract the gas age distributions in ice layers after the removal of the anomalous layers based on comparison with a weakly smoothed record. It is particularly adapted for the conditions of the East Antarctic plateau, as it helps to characterize smoothing for a large range of very low-temperature and low-accumulation conditions.

scholarly journals Analytical constraints on layered gas trapping and smoothing of atmospheric variability in ice under low accumulation conditions

2017 ◽  
Author(s):  
Kévin Fourteau ◽  
Xavier Faïn ◽  
Patricia Martinerie ◽  
Amaëlle Landais ◽  
Alexey A. Ekaykin ◽  
...  
Keyword(s):  
Ice Core ◽  
Flow Analysis ◽  
Atmospheric Composition ◽  
Atmospheric Variability ◽  
High Accumulation ◽  
Antarctic Plateau ◽  
Mixing Ratios ◽  
Gas Trapping ◽  
Continuous Flow Analysis ◽  
Concentration Changes

Abstract. We investigate for the first time through continuous measurements the loss and alteration of past atmospheric information from air trapping mechanisms under low accumulation conditions. Methane concentration changes were measured over the Dansgaard-Oeschger event 17 (D0-17, ~ 60,000 yrBP) in the Antarctic Vostok 4G-2 ice core. Measurements were performed using continuous-flow analysis combined with laser spectroscopy. The results highlight many anomalous layers at the centimeter scale, unevenly distributed along the ice core. The anomalous methane mixing ratios differ from those in the immediate surrounding layers by up to 50 ppbv. This phenomenon can be theoretically reproduced by a simple layered trapping model, creating very localized gas age scale inversions. We propose a method for cleaning the record of anomalous values which aims at minimizing the bias in the overall signal. Once the layered-trapping induced anomalies are removed from the record, the DO-17 appears to be smoother than its equivalent record from the high accumulation WAIS Divide ice core. This is expected due to the slower sinking and densification speeds of firn layers at lower accumulation. However and surprisingly, the degree of smoothing appears similar between modern and DO-17 conditions at Vostok. This suggests that glacial records of trace gases from low accumulation sites in the East Antarctic plateau can provide a better time resolution of past atmospheric composition changes than usually expected. We also developed a method to extract the gas age distributions in ice layers that can be applied even for sites without firn-air measurements. It is particularly adapted for the conditions of the East Antarctic plateau, as it helps to characterize smoothing for a large range of very low temperature and accumulation conditions.

scholarly journals Assessment of Tropospheric Concentrations of NO2 from the TROPOMI/Sentinel-5 Precursor for the Estimation of Long-Term Exposure to Surface NO2 over South Korea

2021 ◽  
Vol 13 (10) ◽  
pp. 1877
Author(s):  
Ukkyo Jeong ◽  
Hyunkee Hong
Keyword(s):  
South Korea ◽  
Spatial Resolution ◽  
Atmospheric Composition ◽  
Mixing Ratio ◽  
Mean Values ◽  
Mixing Ratios ◽  
Tropospheric No2 ◽  
Korean Ministry ◽  
Surface Mixing ◽  
Rural Sites

Since April 2018, the TROPOspheric Monitoring Instrument (TROPOMI) has provided data on tropospheric NO2 column concentrations (CTROPOMI) with unprecedented spatial resolution. This study aims to assess the capability of TROPOMI to acquire high spatial resolution data regarding surface NO2 mixing ratios. In general, the instrument effectively detected major and moderate sources of NO2 over South Korea with a clear weekday–weekend distinction. We compared the CTROPOMI with surface NO2 mixing ratio measurements from an extensive ground-based network over South Korea operated by the Korean Ministry of Environment (SKME; more than 570 sites), for 2019. Spatiotemporally collocated CTROPOMI and SKME showed a moderate correlation (correlation coefficient, r = 0.67), whereas their annual mean values at each site showed a higher correlation (r = 0.84). The CTROPOMI and SKME were well correlated around the Seoul metropolitan area, where significant amounts of NO2 prevailed throughout the year, whereas they showed lower correlation at rural sites. We converted the tropospheric NO2 from TROPOMI to the surface mixing ratio (STROPOMI) using the EAC4 (ECMWF Atmospheric Composition Reanalysis 4) profile shape, for quantitative comparison with the SKME. The estimated STROPOMI generally underestimated the in-situ value obtained, SKME (slope = 0.64), as reported in previous studies.

scholarly journals The influence of typhoons on atmospheric composition deduced from IAGOS measurements over Taipei

2020 ◽  
Vol 20 (6) ◽  
pp. 3945-3963
Author(s):  
Frank Roux ◽  
Hannah Clark ◽  
Kuo-Ying Wang ◽  
Susanne Rohs ◽  
Bastien Sauvage ◽  
...  
Keyword(s):  
Carbon Monoxide ◽  
Relative Humidity ◽  
Tropical Cyclones ◽  
Marine Boundary Layer ◽  
Chemical Species ◽  
Atmospheric Composition ◽  
Commercial Aircraft ◽  
Regular Feature ◽  
Mixing Ratios ◽  
The Vertical Distribution

Abstract. The research infrastructure IAGOS (In-Service Aircraft for a Global Observing System) equips commercial aircraft with instruments to monitor the composition of the atmosphere during flights around the world. In this article, we use data from two China Airlines aircraft based in Taipei (Taiwan) which provided daily measurements of ozone, carbon monoxide and water vapour throughout the summer of 2016. We present time series, from the surface to the upper troposphere, of ozone, carbon monoxide and relative humidity near Taipei, focusing on periods influenced by the passage of typhoons. We examine landing and take-off profiles in the vicinity of tropical cyclones using ERA-5 reanalyses to elucidate the origin of the anomalies in the vertical distribution of these chemical species. Results indicate a high ozone content in the upper- to middle-troposphere track of the storms. The high ozone mixing ratios are generally correlated with potential vorticity and anti-correlated with relative humidity, suggesting stratospheric origin. These results suggest that tropical cyclones participate in transporting air from the stratosphere to troposphere and that such transport could be a regular feature of typhoons. After the typhoons passed Taiwan, the tropospheric column was filled with substantially lower ozone mixing ratios due to the rapid uplift of marine boundary layer air. At the same time, the relative humidity increased, and carbon monoxide mixing ratios fell. Locally, therefore, the passage of typhoons has a positive effect on air quality at the surface, cleansing the atmosphere and reducing the mixing ratios of pollutants such as CO and O3.

scholarly journals One-Year Characterization and Reactivity of Isoprene and Its Impact on Surface Ozone Formation at A Suburban Site in Guangzhou, China

Atmosphere ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 201 ◽  
Author(s):  
Yu Zou ◽  
Xue Jiao Deng ◽  
Tao Deng ◽  
Chang Qin Yin ◽  
Fei Li
Keyword(s):  
Surface Ozone ◽  
Atmospheric Composition ◽  
Anthropogenic Factors ◽  
Mixing Ratio ◽  
Night Time ◽  
Subtropical Zone ◽  
Guangzhou City ◽  
Mixing Ratios ◽  
One Year ◽  
Suburban Site

Isoprene has a potentially large effect on ozone (O3) formation in the subtropical, highly polluted city of Guangzhou. Online measurements of isoprene in Guangzhou city are scarce; thus, isoprene levels were monitored for one year at the Guangzhou Panyu Atmospheric Composition Station (GPACS), a suburban site in Guangzhou, using an online gas chromatography-flame ionization detector (GC–FID) system to investigate the characterization and reactivity of isoprene and its effect on the O3 peak profile in different seasons. The results showed that the daily average mixing ratios of isoprene at GPACS were 0.40, 2.20, 1.40, and 0.13 mixing ratio by volume (ppbv) in spring, summer, autumn, and winter, respectively. These values were considerably higher than the mixing ratios of isoprene in the numerous other subtropical and temperate cities around the world. Furthermore, isoprene ranked first with regard to O3 formation potential (OFP) and propylene-equivalent mixing ratio among 56 measured non–methane hydrocarbons (NMHCs). The ratios of isoprene to cis-2-butene, an exhaust tracer, were determined to estimate the fractions of biogenic and anthropogenic emissions. The results revealed a much greater contribution from biogenic than anthropogenic factors during the daytime in all four seasons. In addition, night-time isoprene emissions were mostly associated with vehicles in winter, and the residual isoprene that remained after photochemical loss during the daytime also persisted into the night. The high levels of isoprene in summer and autumn may cause the strong and broad peaks of the O3 profile because of its association with the most favorable meteorological conditions (e.g., high temperature and intense solar radiation) and the highest OH mixing ratio, which could affect human health by exposing people to a high O3 mixing ratio for prolonged periods. The lower mixing ratios of isoprene resulted in a weak and sharp peak in the O3 profile in both spring and winter. The high level of isoprene in the subtropical zone could accentuate its large impact on atmospheric oxidant capacity and air quality in Guangzhou city.

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