scholarly journals Representativeness of the IAGOS airborne measurements in the lower troposphere

Elem Sci Anth ◽  
2018 ◽  
Vol 6 ◽  
Author(s):  
H. Petetin ◽  
M. Jeoffrion ◽  
B. Sauvage ◽  
G. Athier ◽  
R. Blot ◽  
...  
Keyword(s):  
Air Quality ◽  
Lower Troposphere ◽  
Monitoring Network ◽  
Ratio Distribution ◽  
Airborne Measurements ◽  
Mixing Ratios ◽  
The Difference ◽  
The Vertical Distribution ◽  
Local Emissions

In the framework of the In Service Aircraft for Global Observing System (IAGOS) program, airborne in-situ O3 and CO measurements are performed routinely using in-service aircraft, providing vertical profiles from the surface to about 10–12 km. Due to the specificity of IAGOS measurements (measurements around busy international airports), uncertainties exist on their representativeness in the lower troposphere as they may be impacted by emissions related to airport activities and/or other aircraft. In this study, we thus investigate how the IAGOS measurements in the lower troposphere compare with nearby surface stations (from the local Air Quality monitoring network (AQN)) and more distant regional surface stations (from the Global Atmospheric Watch (GAW) network). The study focuses on Frankfurt but some results at other European airports (Vienna, Paris) are also discussed. Results indicate that the IAGOS observations close to the surface do not appear to be strongly impacted by local emissions related to airport activities. In terms of mixing ratio distribution, seasonal variations and trends, the CO and O3 mixing ratios measured by IAGOS in the first few hundred metres above the surface have similar characteristics to the mixing ratios measured at surrounding urban background stations. Higher in altitude, both the difference with data from the local AQN and the consistency with the GAW regional stations are higher, which indicates a larger representativeness of the IAGOS data. Despite few quantitative differences with Frankfurt, consistent results are obtained in the two other cities Vienna and Paris. Based on 11 years of data (2002–2012), this study thus demonstrates that IAGOS observations in the lowest troposphere can be used as a complement to surface stations to study the air quality in/around the agglomeration, providing important information on the vertical distribution of pollution.

scholarly journals Tunable diode laser in-situ CH<sub>4</sub> measurements aboard the CARIBIC passenger aircraft: instrument performance assessment

2014 ◽  
Vol 7 (3) ◽  
pp. 743-755 ◽  
Author(s):  
C. Dyroff ◽  
A. Zahn ◽  
S. Sanati ◽  
E. Christner ◽  
A. Rauthe-Schöch ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Correlation Study ◽  
Tunable Diode Laser ◽  
Long Distance ◽  
Airborne Measurements ◽  
Mixing Ratios ◽  
Flight Level ◽  
Passenger Aircraft ◽  
The Tropics

Abstract. A laser spectrometer for automated monthly measurements of methane (CH4) mixing ratios aboard the CARIBIC passenger aircraft is presented. The instrument is based on a commercial Fast Greenhouse Gas Analyser (FGGA, Los Gatos Res.), which was adapted to meet the requirements imposed by unattended airborne operation. It was characterised in the laboratory with respect to instrument stability, precision, cross sensitivity to H2O, and accuracy. For airborne operation, a calibration strategy is described that utilises CH4 measurements obtained from flask samples taken during the same flights. The precision of airborne measurements is 2 ppb for 10 s averages. The accuracy at aircraft cruising altitude is 3.85 ppb. During aircraft ascent and descent, where no flask samples were obtained, instrumental drifts can be less accurately determined and the uncertainty is estimated to be 12.4 ppb. A linear humidity bias correction was applied to the CH4 measurements, which was most important in the lower troposphere. On average, the correction bias was around 6.5 ppb at an altitude of 2 km, and negligible at cruising flight level. Observations from 103 long-distance flights are presented that span a large part of the northern hemispheric upper troposphere and lowermost stratosphere (UT/LMS), with occasional crossing of the tropics on flights to southern Africa. These accurate data mark the largest UT/LMS in-situ CH4 dataset worldwide. An example of a tracer-tracer correlation study with ozone is given, highlighting the possibility for accurate cross-tropopause transport analyses.

scholarly journals Tunable diode laser in-situ CH<sub>4</sub> measurements aboard the CARIBIC passenger aircraft: instrument performance assessment

2013 ◽  
Vol 6 (5) ◽  
pp. 9225-9261 ◽  
Author(s):  
C. Dyroff ◽  
A. Zahn ◽  
S. Sanati ◽  
E. Christner ◽  
A. Rauthe-Schöch ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Correlation Study ◽  
Tunable Diode Laser ◽  
Long Distance ◽  
Airborne Measurements ◽  
Mixing Ratios ◽  
Laboratory Characterization ◽  
Passenger Aircraft ◽  
The Tropics

Abstract. A laser spectrometer for automated monthly measurements of methane (CH4) mixing ratios aboard the CARIBIC passenger aircraft is presented. The instrument is based on a commercial Fast Greenhouse Gas Analyzer (FGGA, Los Gatos Res.), which was adapted to meet the requirements imposed by unattended airborne employment. The modified instrument is described. A laboratory characterization was performed to determine the instrument stability, precision, cross sensitivity to H2O, and accuracy. For airborne operation a calibration strategy is described, that utilizes CH4 measurements obtained from flask samples taken during the same flights. The precision of airborne measurements is 2 ppbv for 10 s averages. The accuracy at aircraft cruising altitude is 3.85 ppbv. During aircraft ascent and descent, where no flask samples were obtained, instrumental drifts can be less accurately considered and the uncertainty is estimated to be 12.4 ppbv. A linear humidity bias correction was applied to the CH4 measurements, which was most important in the lower troposphere. On average, the correction bias was around 6.5 ppbv at an altitude of 2 km, and negligible at cruising flight level. Observations from 103 long-distance flights are presented that span a large part of the northern hemispheric upper troposphere and lowermost stratosphere (UT/LMS), with occasional crossing of the tropics on flights to southern Africa. These accurate data mark the largest UT/LMS in-situ CH4 dataset worldwide. An example of a tracer-tracer correlation study with ozone is given, highlighting the possibility for accurate cross-tropopause transport analyses.

scholarly journals The vertical distribution of biomass burning pollution over tropical South America from aircraft in situ measurements during SAMBBA

2019 ◽  
Vol 19 (9) ◽  
pp. 5771-5790 ◽  
Author(s):  
Eoghan Darbyshire ◽  
William T. Morgan ◽  
James D. Allan ◽  
Dantong Liu ◽  
Michael J. Flynn ◽  
...  
Keyword(s):  
Air Quality ◽  
South America ◽  
Vertical Distribution ◽  
Biomass Burning ◽  
Mixing Layer ◽  
Free Troposphere ◽  
The West ◽  
The Vertical Distribution ◽  
Tropical South America

Abstract. We examine processes driving the vertical distribution of biomass burning pollution following an integrated analysis of over 200 pollutant and meteorological profiles measured in situ during the South AMerican Biomass Burning Analysis (SAMBBA) field experiment. This study will aid future work examining the impact of biomass burning on weather, climate and air quality. During the dry season there were significant contrasts in the composition and vertical distribution of haze between western and eastern regions of tropical South America. Owing to an active or residual convective mixing layer, the aerosol abundance was similar from the surface to ∼1.5 km in the west and ∼3 km in the east. Black carbon mass loadings were double as much in the east (1.7 µg m−3) than the west (0.85 µg m−3), but aerosol scattering coefficients at 550 nm were similar (∼120 Mm−1), as too were CO near-surface concentrations (310–340 ppb). We attribute these contrasts to the more flaming combustion of Cerrado fires in the east and more smouldering combustion of deforestation and pasture fires in the west. Horizontal wind shear was important in inhibiting mixed layer growth and plume rise, in addition to advecting pollutants from the Cerrado regions into the remote tropical forest of central Amazonia. Thin layers above the mixing layer indicate the roles of both plume injection and shallow moist convection in delivering pollution to the lower free troposphere. However, detrainment of large smoke plumes into the upper free troposphere was very infrequently observed. Our results reiterate that thermodynamics control the pollutant vertical distribution and thus point to the need for correct model representation so that the spatial distribution and vertical structure of biomass burning smoke is captured. We observed an increase of aerosol abundance relative to CO with altitude both in the background haze and plume enhancement ratios. It is unlikely associated with thermodynamic partitioning, aerosol deposition or local non-fire sources. We speculate it may be linked to long-range transport from West Africa or fire combustion efficiency coupled to plume injection height. Further enquiry is required to explain the phenomenon and explore impacts on regional climate and air quality.

scholarly journals Aircraft validation of Aura Tropospheric Emission Spectrometer retrievals of HDO / H<sub>2</sub>O

2014 ◽  
Vol 7 (9) ◽  
pp. 3127-3138 ◽  
Author(s):  
R. L. Herman ◽  
J. E. Cherry ◽  
J. Young ◽  
J. M. Welker ◽  
D. Noone ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Standard Deviation ◽  
Lower Troposphere ◽  
Temporal Variations ◽  
Observation Error ◽  
Free Troposphere ◽  
Data Set ◽  
Airborne Measurements

Abstract. The EOS (Earth Observing System) Aura Tropospheric Emission Spectrometer (TES) retrieves the atmospheric HDO / H2O ratio in the mid-to-lower troposphere as well as the planetary boundary layer. TES observations of water vapor and the HDO isotopologue have been compared with nearly coincident in situ airborne measurements for direct validation of the TES products. The field measurements were made with a commercially available Picarro L1115-i isotopic water analyzer on aircraft over the Alaskan interior boreal forest during the three summers of 2011 to 2013. TES special observations were utilized in these comparisons. The TES averaging kernels and a priori constraints have been applied to the in situ data, using version 5 (V005) of the TES data. TES calculated errors are compared with the standard deviation (1σ) of scan-to-scan variability to check consistency with the TES observation error. Spatial and temporal variations are assessed from the in situ aircraft measurements. It is found that the standard deviation of scan-to-scan variability of TES δD is ±34.1‰ in the boundary layer and ± 26.5‰ in the free troposphere. This scan-to-scan variability is consistent with the TES estimated error (observation error) of 10–18‰ after accounting for the atmospheric variations along the TES track of ±16‰ in the boundary layer, increasing to ±30‰ in the free troposphere observed by the aircraft in situ measurements. We estimate that TES V005 δD is biased high by an amount that decreases with pressure: approximately +123‰ at 1000 hPa, +98‰ in the boundary layer and +37‰ in the free troposphere. The uncertainty in this bias estimate is ±20‰. A correction for this bias has been applied to the TES HDO Lite Product data set. After bias correction, we show that TES has accurate sensitivity to water vapor isotopologues in the boundary layer.

scholarly journals Evaluating calibration strategies for isotope ratio infrared spectroscopy for atmospheric <sup>13</sup>CO<sub>2</sub>/<sup>12</sup>CO<sub>2</sub> measurement

2013 ◽  
Vol 6 (1) ◽  
pp. 795-823 ◽  
Author(s):  
X.-F. Wen ◽  
Y. Meng ◽  
X.-Y. Zhang ◽  
X.-M. Sun ◽  
X. Lee
Keyword(s):  
Infrared Spectroscopy ◽  
Concentration Dependence ◽  
Isotope Ratio ◽  
High Sensitivity ◽  
Linear Interpolation ◽  
Mixing Ratios ◽  
The Difference ◽  
Ambient Measurements ◽  
Better Than

Abstract. Isotope ratio infrared spectroscopy (IRIS) provides an in-situ technique for measuring δ13C in atmospheric CO2. A number of methods have been proposed for calibrating the IRIS measurements, but few studies have systematically evaluated their accuracy for atmospheric applications. In this study, we carried out laboratory and ambient measurements with two commercial IRIS analyzers and compared the accuracy of four calibration strategies. We found that calibration based on the 12C and 13C mixing ratios (Bowling et al., 2003) and that based on linear interpolation of the measured delta using the mixing ratio of the major isotopologue (Lee et al., 2005) yielded accuracy better than 0.06‰. Over a 7-day atmospheric measurement in Beijing, the two analyzers differed by 9.44 ± 1.65‰ (mean ± 1 standard deviation of hourly values) before calibration and agreed to within −0.02 ± 0.18‰ after properly calibration. However, even after calibration the difference between the two analyzers showed a slight correlation with concentration, and this concentration dependence propagated through the Keeling analysis resulting in a much larger difference of 2.44‰ for the Keeling intercept. The high sensitivity of the Keeling analysis to the concentration dependence underscores the challenge of IRIS for atmospheric research.

scholarly journals Impacts of different characterizations of large-scale background on simulated regional-scale ozone over the continental United States

2018 ◽  
Vol 18 (5) ◽  
pp. 3839-3864 ◽  
Author(s):  
Christian Hogrefe ◽  
Peng Liu ◽  
George Pouliot ◽  
Rohit Mathur ◽  
Shawn Roselle ◽  
...  
Keyword(s):  
Air Quality ◽  
Boundary Conditions ◽  
Large Scale ◽  
Surface Ozone ◽  
Regional Scale ◽  
Model Performance ◽  
Lower Troposphere ◽  
Substantial Impact ◽  
Mixing Ratios ◽  
Scale Models

Abstract. This study analyzes simulated regional-scale ozone burdens both near the surface and aloft, estimates process contributions to these burdens, and calculates the sensitivity of the simulated regional-scale ozone burden to several key model inputs with a particular emphasis on boundary conditions derived from hemispheric or global-scale models. The Community Multiscale Air Quality (CMAQ) model simulations supporting this analysis were performed over the continental US for the year 2010 within the context of the Air Quality Model Evaluation International Initiative (AQMEII) and Task Force on Hemispheric Transport of Air Pollution (TF-HTAP) activities. CMAQ process analysis (PA) results highlight the dominant role of horizontal and vertical advection on the ozone burden in the mid-to-upper troposphere and lower stratosphere. Vertical mixing, including mixing by convective clouds, couples fluctuations in free-tropospheric ozone to ozone in lower layers. Hypothetical bounding scenarios were performed to quantify the effects of emissions, boundary conditions, and ozone dry deposition on the simulated ozone burden. Analysis of these simulations confirms that the characterization of ozone outside the regional-scale modeling domain can have a profound impact on simulated regional-scale ozone. This was further investigated by using data from four hemispheric or global modeling systems (Chemistry – Integrated Forecasting Model (C-IFS), CMAQ extended for hemispheric applications (H-CMAQ), the Goddard Earth Observing System model coupled to chemistry (GEOS-Chem), and AM3) to derive alternate boundary conditions for the regional-scale CMAQ simulations. The regional-scale CMAQ simulations using these four different boundary conditions showed that the largest ozone abundance in the upper layers was simulated when using boundary conditions from GEOS-Chem, followed by the simulations using C-IFS, AM3, and H-CMAQ boundary conditions, consistent with the analysis of the ozone fields from the global models along the CMAQ boundaries. Using boundary conditions from AM3 yielded higher springtime ozone columns burdens in the middle and lower troposphere compared to boundary conditions from the other models. For surface ozone, the differences between the AM3-driven CMAQ simulations and the CMAQ simulations driven by other large-scale models are especially pronounced during spring and winter where they can reach more than 10 ppb for seasonal mean ozone mixing ratios and as much as 15 ppb for domain-averaged daily maximum 8 h average ozone on individual days. In contrast, the differences between the C-IFS-, GEOS-Chem-, and H-CMAQ-driven regional-scale CMAQ simulations are typically smaller. Comparing simulated surface ozone mixing ratios to observations and computing seasonal and regional model performance statistics revealed that boundary conditions can have a substantial impact on model performance. Further analysis showed that boundary conditions can affect model performance across the entire range of the observed distribution, although the impacts tend to be lower during summer and for the very highest observed percentiles. The results are discussed in the context of future model development and analysis opportunities.

scholarly journals Airborne observations and modeling of springtime stratosphere-to-troposphere transport over California

2013 ◽  
Vol 13 (4) ◽  
pp. 10157-10192 ◽  
Author(s):  
E. L. Yates ◽  
L. T. Iraci ◽  
M. C. Roby ◽  
R. B. Pierce ◽  
M. S. Johnson ◽  
...  
Keyword(s):  
Air Quality ◽  
Free Troposphere ◽  
Air Mass ◽  
Air Masses ◽  
Airborne Measurements ◽  
Mixing Ratios ◽  
Stratospheric Intrusion ◽  
Tropospheric O3 ◽  
Carbon Dioxide Co2 ◽  
The Impact

Abstract. Stratosphere-to-troposphere transport (STT) results in air masses of stratospheric origin intruding into the free troposphere. Once in the free troposphere, O3-rich stratospheric air can be transported and mixed with tropospheric air masses, contributing to the tropospheric O3 budget. Evidence of STT can be identified based on the differences in the trace gas composition of the two regions. Because ozone (O3) is present in such large quantities in the stratosphere compared to the troposphere, it is frequently used as a tracer for STT events. This work reports on airborne in situ measurements of O3 and other trace gases during two STT events observed over California, USA. The first, on 14 May 2012, was associated with a cut-off low, and the second, on 5 June 2012, occurred during a post-trough, building ridge event. In each STT event, airborne measurements identified high O3 within a stratospheric intrusion which was observed as low as 3 km above sea level. During both events the stratospheric air mass was characterized by elevated O3 mixing ratios and reduced carbon dioxide (CO2) and water vapor. The reproducible observation of reduced CO2 within the stratospheric air mass supports the use of non-conventional tracers as an additional method for detecting STT. A detailed meteorological analysis of each STT event is presented and observations are interpreted with the Realtime Air Quality Modeling System (RAQMS). The implications of the two STT events are discussed in terms of the impact on the total tropospheric O3 budget and the impact on air quality and policy-making.

scholarly journals In situ measurement of CO<sub>2</sub> and CH<sub>4</sub> from aircraft over northeast China and comparison with OCO-2 data

2019 ◽  
Author(s):  
Xiaoyu Sun ◽  
Minzheng Duan ◽  
Yang Gao ◽  
Rui Han ◽  
Denghui Ji ◽  
...  
Keyword(s):  
Greenhouse Gases ◽  
Northeast China ◽  
In Situ Measurements ◽  
Vertical Profiles ◽  
Large Area ◽  
Mixing Ratios ◽  
Swir Band ◽  
Shortwave Infrared ◽  
The Vertical Distribution

Abstract. Several satellites have been launched to monitor the increasing concentrations of greenhouse gases, especially CO2 and CH4 in the atmosphere, through back-scattered hyperspectral radiance in the shortwave infrared (SWIR) band. The vertical profiles of greenhouse gases and aerosol could strongly affect the results from these instruments. To investigate the effects of the vertical distribution of CO2 on uncertainty in SWIR satellite retrieval results, we conducted observations of the vertical profiles of CO2, CH4, and aerosol particles at 0.6–7 km above sea level using a Beechcraft King Air 350ER in Jiansanjiang (46.77° N, 131.99° E), Heilongjiang province, Northeast China, on August 7–12, 2018. The profiles from this aircraft captured a decrease in CO2 from 2 km to the minimum altitude due to uptake from vegetation at the surface in summer. CH4 measurements showed an average 0.5 ppm increase from 2.0 to 0.6 km, which may result from emissions from the large area of paddy fields below, and a constant mole fraction between 1.951 and 1.976 ppm was recorded at 2 km and above. Comparison of CO2 profiles from a new version of the carbon cycle data assimilation system Tan-Tracker (v1), retrievals from OCO-2 and aircraft measurements was conducted. The results from OCO-2 and the assimilation model system Tan-Tracker captured the vertical structure of CO2 above 3 km, whereas below 3 km, the values from OCO-2 and Tan-Tracker model were lower than those from in situ measurements. Column-averaged CO2 volume mixing ratios calculated from in situ measurements showed biases of −2.39 ± 2.02 ppm and −0.61 ± 0.49 % compared to OCO-2 retrievals.

scholarly journals TransCom N<sub>2</sub>O model inter-comparison – Part 1: Assessing the influence of transport and surface fluxes on tropospheric N<sub>2</sub>O variability

2014 ◽  
Vol 14 (2) ◽  
pp. 2307-2362 ◽  
Author(s):  
R. L. Thompson ◽  
P. K. Patra ◽  
K. Ishijima ◽  
E. Saikawa ◽  
M. Corazza ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Seasonal Cycle ◽  
Large Scale ◽  
Atmospheric Transport ◽  
Lower Troposphere ◽  
Vertical Gradient ◽  
Surface Fluxes ◽  
Meridional Transport ◽  
Mixing Ratios

Abstract. We present a comparison of chemistry-transport models (TransCom-N2O) to examine the importance of atmospheric transport and surface fluxes on the variability of N2O mixing ratios in the troposphere. Six different models and two model variants participated in the inter-comparison and simulations were made for the period 2006 to 2009. In addition to N2O, simulations of CFC-12 and SF6 were made by a subset of four of the models to provide information on the models proficiency in stratosphere-troposphere exchange (STE) and meridional transport, respectively. The same prior emissions were used by all models to restrict differences among models to transport and chemistry alone. Four different N2O flux scenarios totalling between 14 and 17 Tg N yr−1 (for 2005) globally were also compared. The modelled N2O mixing ratios were assessed against observations from in-situ stations, discrete air sampling networks, and aircraft. All models adequately captured the large-scale patterns of N2O and the vertical gradient from the troposphere to the stratosphere and most models also adequately captured the N2O tropospheric growth rate. However, all models underestimated the inter-hemispheric N2O gradient by at least 0.33 ppb (equivalent to 1.5 Tg N), which, even after accounting for an overestimate of emissions in the Southern Ocean of circa 1.0 Tg N, points to a likely underestimate of the Northern Hemisphere source by up to 0.5 Tg N and/or an overestimate of STE in the Northern Hemisphere. Comparison with aircraft data reveal that the models overestimate the amplitude of the N2O seasonal cycle at Hawaii (21° N, 158° W) below circa 6000 m, suggesting an overestimate of the importance of stratosphere to troposphere transport in the lower troposphere at this latitude. In the Northern Hemisphere, most of the models that provided CFC-12 simulations captured the phase of the CFC-12, seasonal cycle, indicating a reasonable representation of the timing of STE. However, for N2O all models simulated a too early minimum by 2 to 3 months owing to errors in the seasonal cycle in the prior soil emissions, which is still not adequately represented by terrestrial biosphere models. In the Southern Hemisphere, most models failed to capture the N2O and CFC-12 seasonality at Cape Grim, Tasmania, and all failed at the South Pole, whereas for SF6, all models could capture the seasonality at all sites, suggesting that there are large errors in modeled vertical transport in high southern latitudes.

scholarly journals Impacts of Different Characterizations of Large-Scale Background on Simulated Regional-Scale Ozone Over the Continental United States

2017 ◽  
Author(s):  
Christian Hogrefe ◽  
Peng Liu ◽  
George Pouliot ◽  
Rohit Mathur ◽  
Shawn Roselle ◽  
...  
Keyword(s):  
Air Quality ◽  
Boundary Conditions ◽  
Large Scale ◽  
Surface Ozone ◽  
Regional Scale ◽  
Model Performance ◽  
Lower Troposphere ◽  
Substantial Impact ◽  
Mixing Ratios ◽  
Scale Models

Abstract. This study analyzes simulated regional-scale ozone burdens both near the surface and aloft, estimates process contributions to these burdens, and calculates the sensitivity of the simulated regional-scale ozone burden to several key model inputs with a particular emphasis on boundary conditions derived from hemispheric or global scale models. The Community Multiscale Air Quality (CMAQ) model simulations supporting this analysis were performed over the continental U.S. for the year 2010 within the context of the Air Quality Model Evaluation International Initiative (AQMEII) and Task Force on Hemispheric Transport of Air Pollution (TF-HTAP) activities. CMAQ Process Analysis (PA) results highlight the dominant role of horizontal and vertical advection on the ozone burden in the mid-to-upper troposphere and lower stratosphere. Vertical mixing, including mixing by convective clouds, couple fluctuations in free tropospheric ozone to ozone in lower layers. Hypothetical bounding scenarios were performed to quantify the effects of emissions, boundary conditions, and ozone dry deposition on the simulated ozone burden. Analysis of these simulations confirms that the characterization of ozone outside the regional-scale modeling domain can have a profound impact on simulated regional-scale ozone. This was further investigated by using data from four hemispheric or global modeling systems (Chemistry – Integrated Forecasting Model (C-IFS), CMAQ extended for hemispheric applications (H-CMAQ), GEOS-Chem, and AM3) to derive alternate boundary conditions for the regional-scale CMAQ simulations. The regional-scale CMAQ simulations using these four different boundary conditions showed that the largest ozone abundance in the upper layers was simulated when using boundary conditions from GEOS-Chem, followed by the simulations using C-IFS, AM3, and H-CMAQ boundary conditions, consistent with the analysis of the ozone fields from the global models along the CMAQ boundaries. Using boundary conditions from AM3 yielded higher springtime ozone columns burdens in the mid- and lower troposphere compared to boundary conditions from the other models. For surface ozone, the differences between the AM3-driven CMAQ simulations and the CMAQ simulations driven by other large-scale models are especially pronounced during spring and winter where they can reach more than 10 ppb for seasonal mean ozone mixing ratios and as much as 15 ppb for domain-averaged daily maximum 8-hr average ozone on individual days. In contrast, the differences between the C-IFS, GEOS-Chem, and H-CMAQ driven regional-scale CMAQ simulations are typically smaller. Comparing simulated surface ozone mixing ratios to observations and computing seasonal and regional model performance statistics revealed that boundary conditions can have a substantial impact on model performance. Further analysis showed that boundary conditions can affect model performance across the entire range of the observed distribution, although the impacts tend to be lower during summer and for the very highest observed percentiles. The results are discussed in the context of future model development and analysis opportunities.

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