scholarly journals A new method to correct the electrochemical concentration cell (ECC) ozonesonde time response and its implications for “background current” and pump efficiency

2020 ◽  
Vol 13 (10) ◽  
pp. 5667-5680
Author(s):  
Holger Vömel ◽  
Herman G. J. Smit ◽  
David Tarasick ◽  
Bryan Johnson ◽  
Samuel J. Oltmans ◽  
...  
Keyword(s):  
Reaction Pathway ◽  
Pump Efficiency ◽  
Background Current ◽  
Buffer Solution ◽  
Fast Reaction ◽  
Concentration Cell ◽  
Upper Troposphere ◽  
Excess Current ◽  
Ozone Concentrations ◽  
Systematic Biases

Abstract. The electrochemical concentration cell (ECC) ozonesonde has been the main instrument for in situ profiling of ozone worldwide; yet, some details of its operation, which contribute to the ozone uncertainty budget, are not well understood. Here, we investigate the time response of the chemical reactions inside the ECC and how corrections can be used to remove some systematic biases. The analysis is based on the understanding that two reaction pathways involving ozone occur inside the ECC that generate electrical currents on two very different timescales. The main fast-reaction pathway with a time constant of about 20 s is due the conversion of iodide to molecular iodine and the generation of two free electrons per ozone molecule. A secondary slow-reaction pathway involving the buffer generates an excess current of about 2 %–10 % with a time constant of about 25 min. This excess current can be interpreted as what has conventionally been considered the “background current”. This contribution can be calculated and removed from the measured current instead of the background current. Here we provide an algorithm to calculate and remove the contribution of the slow-reaction pathway and to correct for the time lag of the fast-reaction pathway. This processing algorithm has been applied to ozonesonde profiles at Costa Rica and during the Central Equatorial Pacific Experiment (CEPEX) as well as to laboratory experiments evaluating the performance of ECC ozonesondes. At Costa Rica, where a 1 % KI, 1/10th buffer solution is used, there is no change in the derived total ozone column; however, in the upper troposphere and lower stratosphere, average reported ozone concentrations increase by up to 7 % and above 30 km decrease by up to 7 %. During CEPEX, where a 1 % KI, full-buffer solution was used, ozone concentrations are increased mostly in the upper troposphere, with no change near the top of the profile. In the laboratory measurements, the processing algorithms have been applied to measurements using the majority of current sensing solutions and using only the stronger pump efficiency correction reported by Johnson et al. (2002). This improves the accuracy of the ECC sonde ozone profiles, especially for low ozone concentrations or large ozone gradients and removes systematic biases relative to the reference instruments. In the surface layer, operational procedures prior to launch, in particular the use of filters, influence how typical gradients above the surface are detected. The correction algorithm may report gradients that are steeper than originally reported, but their uncertainty is strongly influenced by the prelaunch procedures.

scholarly journals A new method to correct the ECC ozone sonde time response and its implications for “background current” and pump efficiency

2020 ◽  
Author(s):  
Holger Vömel ◽  
Herman G. J. Smit ◽  
David Tarasick ◽  
Bryan Johnson ◽  
Samuel J. Oltmans ◽  
...  
Keyword(s):  
Surface Layer ◽  
Costa Rica ◽  
Time Constant ◽  
Reaction Pathway ◽  
Time Response ◽  
Pump Efficiency ◽  
Background Current ◽  
Buffer Solution ◽  
Upper Troposphere ◽  
Slow Reaction

Abstract. The Electrochemical Concentration Cell (ECC) ozonesonde has been the main instrument for in situ profiling of ozone worldwide; yet, some details of its operation, which contribute to the ozone uncertainty budget, are not well understood. Here, we investigate the time response of the chemical reactions inside the ECC and how corrections can be used to remove some systematic biases. The analysis is based on the understanding that two reaction pathways involving ozone occur inside the ECC that generate electrical currents on two very different time scales. A slow reaction pathway involving the buffer with a time constant of about 25 min can be interpreted as what has conventionally been considered the “background current”. This contribution can be calculated and removed from the measured current instead of the “background current”. The remaining fast reaction pathway with a time constant of about 20 s is due the conversion of iodide to molecular iodine and the generation of two free electrons per ozone molecule. Here we provide an algorithm to calculate and remove the contribution of the slow reaction pathway and to correct for the time lag of the faster reaction pathway. This processing algorithm has been applied to ozonesonde profiles at Costa Rica and during the Central Equatorial Pacific Experiment (CEPEX) and to laboratory experiments evaluating the performance of ECC ozonesondes. At Costa Rica, where a 1 % KI, 1/10th buffer solution is used, there is no change in the derived total ozone column; however, in the upper troposphere and lower stratosphere, average reported ozone concentrations increase by up to 7 % and above 30 km decrease by up to 7 %. During CEPEX, where a 1 % KI, full buffer solution was used, ozone concentrations are increased mostly in the upper troposphere with no change near to the top of the profile. In the laboratory measurements, the processing algorithms have been applied to measurements using all current sensing solutions and using only the stronger pump efficiency correction reported by Johnson et al. (2002), which improves the time response of the ECCs and removes some biases relative to the reference instruments. In the surface layer, the correction algorithm shows that ECC ozonesonde measurements are influenced by the operational procedures prior to launch and that typical gradients above the surface layer may be steeper than originally reported.

scholarly journals Ozone sonde cell current measurements and implications for observations of near-zero ozone concentrations in the tropical upper troposphere

2010 ◽  
Vol 3 (2) ◽  
pp. 495-505 ◽  
Author(s):  
H. Vömel ◽  
K. Diaz
Keyword(s):  
Measurement Data ◽  
Laboratory Measurements ◽  
Background Current ◽  
Concentration Cell ◽  
Data Set ◽  
Upper Troposphere ◽  
Ozone Concentrations ◽  
Free Air ◽  
Cell Current ◽  
Tropical Troposphere

Abstract. Laboratory measurements of the Electrochemical Concentration Cell (ECC) ozone sonde cell current using ozone free air as well as defined amounts of ozone reveal that background current measurements during sonde preparation are neither constant as a function of time, nor constant as a function of ozone concentration. Using a background current, measured at a defined timed after exposure to high ozone may often overestimate the real background, leading to artificially low ozone concentrations in the upper tropical troposphere, and may frequently lead to operator dependent uncertainties. Based on these laboratory measurements an improved cell current to partial pressure conversion is proposed, which removes operator dependent variability in the background reading and possible artifacts in this measurement. Data from the Central Equatorial Pacific Experiment (CEPEX) have been reprocessed using the improved background treatment based on these laboratory measurements. In the reprocessed data set near-zero ozone events no longer occur. At Samoa, Fiji, Tahiti, and San Cristóbal, nearly all near-zero ozone concentrations occur in soundings with larger background currents. To a large extent, these events are no longer observed in the reprocessed data set using the improved background treatment.

scholarly journals Ozone sonde cell current measurements and implications for observations of near-zero ozone concentrations in the tropical upper troposphere

2009 ◽  
Vol 2 (6) ◽  
pp. 3153-3181
Author(s):  
H. Vömel ◽  
K. Diaz
Keyword(s):  
Measurement Data ◽  
Laboratory Measurements ◽  
Background Current ◽  
Concentration Cell ◽  
Data Set ◽  
Upper Troposphere ◽  
Ozone Concentrations ◽  
Free Air ◽  
Cell Current ◽  
Tropical Troposphere

Abstract. Laboratory measurements of the Electrochemical Concentration Cell (ECC) ozone sonde cell current using ozone free air as well as defined amounts of ozone reveal that background current measurements during sonde preparation are neither constant as a function of time, nor constant as a function of ozone concentration. Using these background currents in the processing of ECC data may lead to operator dependent uncertainties and may frequently lead to artificially low ozone concentrations in the upper tropical troposphere. Based on these laboratory measurements an improved cell current to partial pressure conversion is proposed, which removes operator dependent variability in the background reading, and possible artifacts in this measurement. Data from the Central Equatorial Pacific Experiment (CEPEX) have been reprocessed using the improved background treatment based on these laboratory measurements. In the reprocessed data set near-zero ozone events no longer occur. At Samoa, Fiji, Tahiti, and San Cristóbal, nearly all near-zero ozone concentrations occur in soundings with larger background currents. To a large extent, these events are no longer observed in the reprocessed data set using the improved background treatment.

The importance of the time response of Electrochemical Concentration Cell (ECC) ozone sondes for measurements of tropical upper tropospheric and lower stratospheric ozone

2021 ◽  
Author(s):  
Holger Vömel ◽  
Ryan Stauffer ◽  
Henry Selkirk ◽  
Anne Thompson ◽  
Jorge Andres Diaz ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Fast Reaction ◽  
Concentration Cell ◽  
Measuring Systems ◽  
Upper Troposphere ◽  
Slow Reaction ◽  
Tropical Troposphere ◽  
Complex Chemistry

<p>Accurate measurements of ozone in the upper tropical troposphere and lower stratosphere (UTLS) are challenging for most measuring systems, yet of great importance for the understanding of the chemical and dynamical processes in this region.</p><p>Balloon-borne observations using Electrochemical Concentration Cell (ECC) ozone sondes are the most widely used in situ technology to measure vertical profiles of ozone in networks such as the Southern Hemisphere ADditional Ozonesondes (SHADOZ) network of tropical and subtropical ozone sonde stations.</p><p>The tropical upper troposphere and the layers of near-zero ozone within the ozone hole are most sensitive to processing and preparation variations that may affect the accuracy and possibly trend estimates of ozone in low ozone regions. It is now appreciated that the complex chemistry within the ECC used to detect ozone exhibits two different time constants (τ<sub>fast</sub>≈20 s, τ<sub>slow</sub>≈25 min), which modify the response of the ECC during a profile. Although not well understood, the chemistry of the slow reaction is likely to represent what has conventionally been assumed a constant “background current”. The fast reaction causes some delay in the response of the ECC to changes in the vertical profile of ozone. Here we show how correcting for both improves the estimate of the lowest ozone concentration in the upper troposphere as well as the steepness of the gradient in the transition into the stratosphere. The steady state bias, which describes the contribution of the slow reaction, is the largest source of uncertainty overall; the response time of the fast reaction dominates the uncertainty in the region of the sharp gradient of ozone above the tropopause.</p>

scholarly journals An automated method for preparing and calibrating electrochemical concentration cell (ECC) ozonesondes

2020 ◽  
Vol 13 (3) ◽  
pp. 1157-1166
Author(s):  
Francis J. Schmidlin ◽  
Bruno A. Hoegger
Keyword(s):  
Partial Pressure ◽  
Digital Calibration ◽  
Automated System ◽  
Current Response ◽  
Background Current ◽  
Concentration Cell ◽  
Automated Method ◽  
Partial Pressures ◽  
Reference Measurements ◽  
Parameters Of Interest

Abstract. In contrast to the legacy manual method used to prepare, condition, and calibrate the electrochemical concentration cell (ECC) ozonesonde, an automated digital calibration bench similar to one developed by MeteoSwiss at Payerne, Switzerland, was established at NASA's Wallops Flight Facility and provides reference measurements of the same ozone partial pressure as measured by the ECC. The purpose of an automated system is to condition and calibrate ECCs before launching on a balloon. Operation of the digital calibration bench is simple and real-time graphs and summaries are available to the operator; all information is archived. The parameters of interest include ozone partial pressure, airflow, temperature, background current, response, and time (real and elapsed). ECCs, prepared with 1.0 % solution of potassium iodide (KI) and full buffer, show increasing partial pressure values when compared to the reference as partial pressures increase. Differences of approximately 5–6 % are noted at 20.0 mPa. Additional tests with different concentrations revealed the Science Pump Corp. (SPC) 6A ECC with 0.5 % KI solution and one-half buffer agreed closer to the reference than the 1.0 % cells. The information gained from the automated system allows a compilation of ECC characteristics, as well as calibrations. The digital calibration bench is recommended for ECC studies as it conserves resources.

scholarly journals Observation of near-zero ozone concentrations in the upper troposphere at mid-latitudes

1998 ◽  
Vol 25 (8) ◽  
pp. 1173-1176 ◽  
Author(s):  
W. E. Davies ◽  
G. Vaughan ◽  
F. M. O'Connor
Keyword(s):  
Upper Troposphere ◽  
Ozone Concentrations

scholarly journals An Automated Method for Preparing and Calibrating Electrochemical Concentration Cell (ECC) Ozonesondes

2019 ◽  
Author(s):  
Francis J. Schmidlin ◽  
Bruno A. Hoegger
Keyword(s):  
Partial Pressure ◽  
Real Time ◽  
Digital Calibration ◽  
Automated System ◽  
Current Response ◽  
Background Current ◽  
Concentration Cell ◽  
Automated Method ◽  
Partial Pressures ◽  
Parameters Of Interest

Abstract. In contrast to the legacy manual method used to prepare, condition, and calibrate the Electrochemical Concentration Cell (ECC) ozonesonde an automated digital calibration bench similar to one developed by MeteoSwiss at Payerne, Switzerland was established at NASA's Wallops Flight Facility and providesreference measurements of the same ozone partial pressure as measured by the ECC. The purpose of an automated system is to condition and calibrate ECC cells before launching on a balloon. Operation of the digital calibration bench is simple and real-time graphs and summaries are available to the operator; all information is archived. The parameters of interest include ozone partial pressure, airflow, temperature, background current, response, and time (real and elapsed). ECC cells, prepared with 1.0 percent solution of potassium iodide (KI) and full buffer, show increasing partial pressure values when compared to the reference as partial pressures increase. Differences of approximately 5–6 percent are noted at 200 nb. Additional tests with different concentrations revealed the Science Pump Corp (SPC) 6A ECC with 0.5 percent KI solution and one-half buffer agreed closer to the reference than the 1.0 percent cells, this is in agreement with results of multi-sonde comparisons obtained during BESOS. The information gained from the automated system allowsa compilation of ECC cell characteristics, as well as calibrations. The digital calibration bench is recommended for ECC studies asit conserves resources.

scholarly journals Foreign influences on tropospheric ozone over East Asia through global atmospheric transport

2019 ◽  
Vol 19 (19) ◽  
pp. 12495-12514 ◽  
Author(s):  
Han Han ◽  
Jane Liu ◽  
Huiling Yuan ◽  
Tijian Wang ◽  
Bingliang Zhuang ◽  
...  
Keyword(s):  
North America ◽  
East Asia ◽  
Tropospheric Ozone ◽  
Large Scale ◽  
Transport Model ◽  
Surface Ozone ◽  
East Asian ◽  
South Asian High ◽  
Upper Troposphere ◽  
Ozone Concentrations

Abstract. Tropospheric ozone in East Asia is influenced by the transport of ozone from foreign regions around the world. However, the magnitudes and variations in such influences remain unclear. This study was performed to investigate the influences using a global chemical transport model, GEOS-Chem, through the tagged ozone and emission perturbation simulations. The results show that foreign ozone is transported to East Asia (20–60∘ N, 95–150∘ E) mainly through the middle and upper troposphere. In East Asia, the influence of foreign ozone increases rapidly with altitude. In the middle and upper troposphere, the regional mean concentrations of foreign ozone range from 32 to 65 ppbv, being 0.8–4.8 times higher than its native counterpart (11–18 ppbv). Annually, ∼60 % of foreign ozone in the East Asian middle and upper troposphere comes from North America (5–13 ppbv) and Europe (5–7 ppbv), as well as from foreign oceanic regions (9–21 ppbv). Over the East Asian tropospheric columns, foreign ozone appears most in spring when ozone concentrations in the foreign regions are high and the westerlies are strong and least in summer when the South Asian High blocks eastward foreign ozone from reaching East Asia south of 35∘ N. At the East Asian surface, the annual mean of foreign ozone concentrations is ∼22.2 ppbv, which is comparable to its native counterpart of ∼20.4 ppbv. In the meantime, the annual mean of anthropogenic ozone concentrations from foreign regions is ∼4.7 ppbv, half of which comes from North America (1.3 ppbv) and Europe (1.0 ppbv). Seasonally, foreign ozone concentrations at the East Asian surface are highest in winter (27.1 ppbv) and lowest in summer (16.5 ppbv). This strong seasonality is largely modulated by the East Asian monsoon (EAM) via its influence on vertical motion. The large-scale subsidence prevailing during the East Asian winter monsoon (EAWM) favours the downdraft of foreign ozone to the surface, while widespread convection in the East Asian summer monsoon (EASM) blocks such transport. Interannually, the variation in foreign ozone at the East Asian surface is found to be closely related to the intensity of the EAM. Specifically, the stronger the EAWM is in a winter, the more ozone from North America and Europe reaches the East Asian surface because of the stronger subsidence behind the East Asian trough. In summer, ozone from South and South-east Asia is reduced in strong EASM years due to weakened south-westerly monsoon winds. This study suggests substantial foreign influences on ozone at the East Asian surface and in its tropospheric columns. It also underscores the importance of the EAM in the seasonal and interannual variations in foreign influences on surface ozone in East Asia.

scholarly journals Variability of winter and summer surface ozone in Mexico City on the intraseasonal timescale

2016 ◽  
Vol 16 (23) ◽  
pp. 15359-15370 ◽  
Author(s):  
Bradford S. Barrett ◽  
Graciela B. Raga
Keyword(s):  
Pacific Ocean ◽  
Mexico City ◽  
Ozone Concentration ◽  
Cloud Cover ◽  
Phase 1 ◽  
Surface Ozone ◽  
Intraseasonal Variability ◽  
Active Phase ◽  
Upper Troposphere ◽  
Ozone Concentrations

Abstract. Surface ozone concentrations in Mexico City frequently exceed the Mexican standard and have proven difficult to forecast due to changes in meteorological conditions at its tropical location. The Madden–Julian Oscillation (MJO) is largely responsible for intraseasonal variability in the tropics. Circulation patterns in the lower and upper troposphere and precipitation are associated with the oscillation as it progresses eastward around the planet. It is typically described by phases (labeled 1 through 8), which correspond to the broad longitudinal location of the active component of the oscillation with enhanced precipitation. In this study we evaluate the intraseasonal variability of winter and summer surface ozone concentrations in Mexico City, which was investigated over the period 1986–2014 to determine if there is a modulation by the MJO that would aid in the forecast of high-pollution episodes. Over 1 000 000 hourly observations of surface ozone from five stations around the metropolitan area were standardized and then binned by active phase of the MJO, with phase determined using the real-time multivariate MJO index. Highest winter ozone concentrations were found in Mexico City on days when the MJO was active and in phase 2 (over the Indian Ocean), and highest summer ozone concentrations were found on days when the MJO was active and in phase 6 (over the western Pacific Ocean). Lowest winter ozone concentrations were found during active MJO phase 8 (over the eastern Pacific Ocean), and lowest summer ozone concentrations were found during active MJO phase 1 (over the Atlantic Ocean). Anomalies of reanalysis-based cloud cover and UV-B radiation supported the observed variability in surface ozone in both summer and winter: MJO phases with highest ozone concentration had largest positive UV-B radiation anomalies and lowest cloud-cover fraction, while phases with lowest ozone concentration had largest negative UV-B radiation anomalies and highest cloud-cover fraction. Furthermore, geopotential height anomalies at 250 hPa favoring reduced cloudiness, and thus elevated surface ozone, were found in both seasons during MJO phases with above-normal ozone concentrations. Similar height anomalies at 250 hPa favoring enhanced cloudiness, and thus reduced surface ozone, were found in both seasons during MJO phases with below-normal ozone concentrations. These anomalies confirm a physical pathway for MJO modulation of surface ozone via modulation of the upper troposphere.

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