scholarly journals Modeling stratospheric intrusion and trans-Pacific transport on tropospheric ozone using hemispheric CMAQ during April 2010 – Part 1: Model evaluation and air mass characterization for stratosphere–troposphere transport

2020 ◽  
Vol 20 (6) ◽  
pp. 3373-3396 ◽  
Author(s):  
Syuichi Itahashi ◽  
Rohit Mathur ◽  
Christian Hogrefe ◽  
Yang Zhang
Keyword(s):  
Model Evaluation ◽  
Tropospheric Ozone ◽  
High Surface ◽  
Model Performance ◽  
Negative Slope ◽  
Subsequent Paper ◽  
Air Mass ◽  
Air Masses ◽  
Stratospheric Intrusion ◽  
Surface O3

Abstract. Stratospheric intrusion and trans-Pacific transport have been recognized as a potential source of tropospheric ozone over the US. The state-of-the-science Community Multiscale Air Quality (CMAQ) modeling system has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ). In this study, H-CMAQ is applied to study the stratospheric intrusion and trans-Pacific transport during April 2010. The results will be presented in two companion papers. In this Part 1 paper, model evaluation for tropospheric ozone (O3) is presented. Observations at the surface, by ozonesondes and airplane, and by satellite across the Northern Hemisphere are used to evaluate the model performance for O3. H-CMAQ is able to capture surface and boundary layer (defined as surface to 750 hPa) O3 with a normalized mean bias (NMB) of −10 %; however, a systematic underestimation with an NMB up to −30 % is found in the free troposphere (defined as 750–250 hPa). In addition, a new air mass characterization method is developed to distinguish influences of stratosphere–troposphere transport (STT) from the effects of photochemistry on O3 levels. This method is developed based on the ratio of O3 and an inert tracer indicating stratospheric O3 to examine the importance of photochemistry, and sequential intrusion from upper layer. During April 2010, on a monthly average basis, the relationship between surface O3 mixing ratios and estimated stratospheric air masses in the troposphere show a slight negative slope, indicating that high surface O3 values are primarily affected by other factors (i.e., emissions), whereas this relationship shows a slight positive slope at elevated sites, indicating that STT has a possible impact at elevated sites. STT shows large day-to-day variations, and STT impacts can either originate from the same air mass over the entire US with an eastward movement found during early April, or stem from different air masses at different locations indicated during late April. Based on this newly established air mass characterization technique, this study can contribute to understanding the role of STT and also the implied importance of emissions leading to high surface O3. Further research focused on emissions is discussed in a subsequent paper (Part 2).

scholarly journals Modeling Trans-Pacific Transport using Hemispheric CMAQ during April 2010: Part 1. Model Evaluation and Air Mass Characterization for the Estimation of Stratospheric Intrusion on Tropospheric Ozone

2019 ◽  
Author(s):  
Syuichi Itahashi ◽  
Rohit Mathur ◽  
Christian Hogrefe ◽  
Yang Zhang
Keyword(s):  
Model Evaluation ◽  
Tropospheric Ozone ◽  
High Surface ◽  
Model Performance ◽  
Threshold Value ◽  
Negative Slope ◽  
Air Mass ◽  
Air Masses ◽  
Mixing Ratios ◽  
Surface O3

Abstract. Trans-Pacific transport has been recognized as a potential source of air pollutants over the U.S.A. The state-of-the-science Community Multiscale Air Quality (CMAQ) Modeling System has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ). In this study, H-CMAQ is applied to study the trans-Pacific transport during April 2010. The results will be presented in two continuous papers. In this part 1 paper, model evaluation for tropospheric ozone (O3) is presented. Observations at the surface, by ozonesondes and airplane, and by satellite across the northern hemisphere are used to evaluate the model performance for O3. H-CMAQ is able to capture surface and boundary layer (defined as surface to 750 hPa) O3 with a normalized mean bias (NMB) of −10 %; however, a systematic underestimation with an NMB up to −30 % is found in the free troposphere (defined as 750–250 hPa). The surface and aloft relative humidity (RH) showed a positive bias around NMB of +10 % or greater. In addition, a new air mass characterization method is developed to distinguish influences of stratosphere-troposphere transport (STT) from the effects of photochemistry on O3 levels. Potential vorticity (PV) is used to diagnose air masses of stratospheric origin and related to RH in order to characterize stratospheric air masses. The tropopause location is determined using a PV threshold value of 2.0 PVU (1 PVU = 10−6 m2 K kg−1 s−1). The constructed PV-RH relationship indicates that PV of 2.0 PVU generally corresponds to RHs of 30–40 %. The air mass characterization method is then developed based on the ratio of O3 and an inert tracer indicating stratospheric O3 to examine the importance of photochemistry, and the PV-RH relationship is used to determine stratospheric intrusions. Over the U.S.A., STT impacts show large day-to-day variations, and STT impacts can either originate from the same air mass over the entire U.S.A. with an eastward movement, or stem from different air masses at different locations. The relationship between surface O3 mixing ratios and estimated stratospheric air masses in the troposphere show a negative slope, indicating that high surface O3 values are primarily affected by other factors (i.e., emissions), whereas this relationship shows an almost flat slope at elevated sites, indicating that STT has a near constant impact at elevated sites. Based on this newly established air mass characterization technique, this study can contribute to understand the role of STT, and also the implied importance of emissions leading to high surface O3. Further research focused on emissions is discussed in a subsequent part 2 paper.

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 Assessment of atmospheric processes driving ozone variations in the subtropical North Atlantic free troposphere

2013 ◽  
Vol 13 (4) ◽  
pp. 1973-1998 ◽  
Author(s):  
E. Cuevas ◽  
Y. González ◽  
S. Rodríguez ◽  
J. C. Guerra ◽  
A. J. Gómez-Peláez ◽  
...  
Keyword(s):  
North America ◽  
North Atlantic ◽  
High Surface ◽  
High Mountain ◽  
Free Troposphere ◽  
Transport Pathways ◽  
Air Masses ◽  
Upper Troposphere ◽  
Summer Time ◽  
Surface O3

Abstract. An analysis of the 22-yr ozone (O3) series (1988–2009) at the subtropical high mountain Izaña~station (IZO; 2373 m a.s.l.), representative of free troposphere (FT) conditions, is presented. Diurnal and seasonal O3 variations as well as the O3 trend (0.19 ± 0.05 % yr−1 or 0.09 ppbv yr−1), are assessed. A climatology of O3 transport pathways using backward trajectories shows that higher O3 values are associated with air masses travelling above 4 km altitude from North America and North Atlantic Ocean, while low O3 is transported from the Saharan continental boundary layer (CBL). O3 data have been compared with PM10, 210Pb, 7Be, potential vorticity (PV) and carbon monoxide (CO). A clear negative logarithmic relationship was observed between PM10 and surface O3 for all seasons. A similar relationship was found between O3 and 210Pb. The highest daily O3 values (90th percentile) are observed in spring and in the first half of summer time. A positive correlation between O3 and PV, and between O3 and 7Be is found throughout the year, indicating that relatively high surface O3 values at IZO originate from the middle and upper troposphere. We find a good correlation between O3 and CO in winter, supporting the hypothesis of long-range transport of photochemically generated O3 from North America. Aged air masses, in combination with sporadic inputs from the upper troposphere, are observed in spring, summer and autumn. In summer time high O3 values seem to be the result of stratosphere-to-troposphere (STT) exchange processes in regions neighbouring the Canary Islands. Since 1995–1996, the North Atlantic Oscillation has changed from a predominantly high positive phase to alternating between negative, neutral or positive phases. This change results in an increased flow of the westerlies in the mid-latitude and subtropical North Atlantic, thus favouring the transport of O3 and its precursors from North America, and a higher frequency of storms over North Atlantic, with a likely higher incidence of STT processes in mid-latitudes. These processes lead to an increase of tropospheric O3 in the subtropical North Atlantic region after 1996 that has been reflected in surface O3 records at IZO.

scholarly journals Modeling Trans-Pacific Transport and Stratospheric Intrusion of Tropospheric Ozone using Hemispheric CMAQ during April 2010: Part 2. Examination of Emission Impacts based on the Higher-order Decoupled Direct Method

2019 ◽  
Author(s):  
Syuichi Itahashi ◽  
Rohit Mathur ◽  
Christian Hogrefe ◽  
Sergey L. Napelenok ◽  
Yang Zhang
Keyword(s):  
East Asia ◽  
Tropospheric Ozone ◽  
Direct Method ◽  
Higher Order ◽  
Positive Correlation ◽  
Mixing Ratios ◽  
Stratospheric Intrusion ◽  
Previous Part ◽  
The Impact ◽  
Surface O3

Abstract. The state-of-the-science Community Multiscale Air Quality (CMAQ) Modeling System which has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ), is applied to study the trans-Pacific transport, a phenomenon recognized as a potential source of air pollution in the U.S.A., during April 2010. The results of this analysis are presented in two parts. In the previous part 1 paper, model evaluation for tropospheric ozone (O3) was presented and an air mass characterization method was developed. Results from applying this newly established method pointed to the importance of emissions as the factor to enhance surface O3 mixing ratio over the U.S.A. In this subsequent part 2 paper, emission impacts are examined based on mathematically rigorous sensitivity analysis using the higher-order decoupled direct method (HDDM) implemented in H-CMAQ. The HDDM sensitivity coefficients indicate the presence of a NOx-sensitive regime during April 2010 over most of the northern hemisphere. By defining emission source regions over the U.S.A. and East Asia, impacts from these emission sources are examined. At the surface during April 2010, the emission impacts of the U.S.A. and East Asia are comparable over the western U.S.A. with a magnitude of about 3 ppbv impacts on a monthly mean of all hours basis whereas the impact of domestic emissions dominates over the eastern U.S.A. with a magnitude of about 10 ppbv impacts on a monthly mean basis. The positive correlation (r = 0.63) between surface O3 mixing ratios and domestic emission impacts is confirmed. In contrast, the relationship between surface O3 mixing ratios and emission impacts from East Asia exhibits a flat slope when considering the entire U.S.A. However, this relationship has strong regional differences between the western and eastern U.S.A.; the western region exhibits a positive correlation (r = 0.36–0.38) whereas the latter exhibits a flat slope (r 

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

2013 ◽  
Vol 13 (24) ◽  
pp. 12481-12494 ◽  
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, ozone (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 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 cutoff 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 the stratospheric intrusion, which were 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 Assessment of atmospheric processes driving ozone variations in the subtropical North Atlantic free troposphere

2012 ◽  
Vol 12 (10) ◽  
pp. 28385-28450 ◽  
Author(s):  
E. Cuevas ◽  
Y. González ◽  
S. Rodríguez ◽  
J. C. Guerra ◽  
A. J. Gómez-Peláez ◽  
...  
Keyword(s):  
North America ◽  
North Atlantic ◽  
High Surface ◽  
High Mountain ◽  
Free Troposphere ◽  
Transport Pathways ◽  
Air Masses ◽  
Upper Troposphere ◽  
Summer Time ◽  
Surface O3

Abstract. An analysis of the 22-yr ozone (O3) series (1988–2009) at the subtropical high mountain Izaña station (IZO; 2373 m a.s.l.), representative of free troposphere (FT) conditions, is presented. Diurnal and seasonal O3 variations as well as the O3 trend (0.19 ± 0.05% yr−1 or 0.09 ppbv yr−), are assessed. A climatology of O3 transport pathways using backward trajectories shows that higher O3 values are associated with air masses traveling above 4 km altitude from North America and North Atlantic Ocean, while low O3 is transported from the Saharan continental boundary layer (CBL). O3 data have been compared with PM10, 210Pb, 7Be, potential vorticity (PV) and carbon monoxide (CO). A clear negative logarithmic relationship was observed between PM10 and surface O3 for all seasons. A similar relationship was found between O3 and 210Pb, but only for the summer-time. The highest daily O3 values (90th percentile) are observed in spring and in the first half of summer-time. A positive correlation between O3 and PV, and between O3 and 7Be is found throughout the year, indicating that relatively high surface O3 values at IZO originate from the middle and upper troposphere. At IZO we find a~good correlation between O3 and CO in winter, supporting the hypothesis of long-range transport of photochemically generated O3 from North America. Aged air masses, in combination with sporadic inputs from the upper troposphere, are observed in spring, summer and autumn. In summer-time high O3 values seem to be the result of stratosphere-to-troposphere (STT) exchange processes in regions neighbouring the Canary Islands. Since 1995–1996, the North Atlantic Oscillation has changed from a predominantly high positive phase to alternating between negative, neutral or positive phases. This change results in an increased flow of the westerlies in the mid-latitude and subtropical North Atlantic, thus favouring the transport of O3 and its precursors from North America, and a~higher frequency of storms over North Atlantic, with a~likely higher incidence of STT processes in mid latitudes. These processes lead to an increase of tropospheric O3 in the subtropical North Atlantic region after 1996 that has been reflected in surface O3 records at IZO.

scholarly journals Modeling stratospheric intrusion and trans-Pacific transport on tropospheric ozone using hemispheric CMAQ during April 2010 – Part 2: Examination of emission impacts based on the higher-order decoupled direct method

2020 ◽  
Vol 20 (6) ◽  
pp. 3397-3413 ◽  
Author(s):  
Syuichi Itahashi ◽  
Rohit Mathur ◽  
Christian Hogrefe ◽  
Sergey L. Napelenok ◽  
Yang Zhang
Keyword(s):  
Sensitivity Analysis ◽  
East Asia ◽  
Tropospheric Ozone ◽  
Direct Method ◽  
Free Troposphere ◽  
Air Mass ◽  
Mixing Ratios ◽  
The Us ◽  
The Impact ◽  
Surface O3

Abstract. The state-of-the-science Community Multiscale Air Quality (CMAQ) modeling system, which has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ), is applied to study the trans-Pacific transport, a phenomenon recognized as a potential source of air pollution in the US, during April 2010. The results of this analysis are presented in two parts. In the previous paper (Part 1), model evaluation for tropospheric ozone (O3) was presented and an air mass characterization method was developed. Results from applying this newly established method pointed to the importance of emissions as the factor to enhance the surface O3 mixing ratio over the US. In this subsequent paper (Part 2), emission impacts are examined based on mathematically rigorous sensitivity analysis using the higher-order decoupled direct method (HDDM) implemented in H-CMAQ. The HDDM sensitivity coefficients indicate the presence of a NOx-sensitive regime during April 2010 over most of the Northern Hemisphere. By defining emission source regions over the US and east Asia, impacts from these emission sources are examined. At the surface, during April 2010, the emission impacts of the US and east Asia are comparable over the western US with a magnitude of about 3 ppbv impacts on monthly mean O3 all-hour basis, whereas the impact of domestic emissions dominates over the eastern US with a magnitude of about 10 ppbv impacts on monthly mean O3. The positive correlation (r=0.63) between surface O3 mixing ratios and domestic emission impacts is confirmed. In contrast, the relationship between surface O3 mixing ratios and emission impacts from east Asia exhibits a flat slope when considering the entire US. However, this relationship has strong regional differences between the western and eastern US; the western region exhibits a positive correlation (r=0.36–0.38), whereas the latter exhibits a flat slope (r < 0.1). Based on the comprehensive evaluation of H-CMAQ, we extend the sensitivity analysis for O3 aloft. The results reveal the significant impacts of emissions from east Asia on the free troposphere (defined as 750 to 250 hPa) over the US (impacts of more than 5 ppbv) and the dominance of stratospheric air mass on upper model layer (defined as 250 to 50 hPa) over the US (impacts greater than 10 ppbv). Finally, we estimate changes of trans-Pacific transport by taking into account recent emission trends from 2010 to 2015 assuming the same meteorological condition. The analysis suggests that the impact of recent emission changes on changes in the contribution of trans-Pacific transport to US O3 levels was insignificant at the surface level and was small (less than 1 ppbv) over the free troposphere.

scholarly journals The Impact of Future Emission Policies on Tropospheric Ozone using a Parameterised Approach

2018 ◽  
Author(s):  
Steven Turnock ◽  
Oliver Wild ◽  
Frank Dentener ◽  
Yanko Davila ◽  
Louisa Emmons ◽  
...  
Keyword(s):  
Air Quality ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Source Attribution ◽  
The Future ◽  
Future Emission ◽  
Tropospheric O3 ◽  
Near Term ◽  
The Impact ◽  
Surface O3

Abstract. This study quantifies future changes in tropospheric ozone (O3) using a simple parameterisation of source-receptor relationships based on simulations from a range of models participating in the Task Force on Hemispheric Transport of Air Pollutants (TF-HTAP) experiments. Surface and tropospheric O3 changes are calculated globally and across 16 regions from perturbations in precursor emissions (NOx, CO, VOCs) and methane (CH4) abundance. A source attribution is provided for each source region along with an estimate of uncertainty based on the spread of the results from the models. Tests against model simulations using HadGEM2-ES confirm that the approaches used within the parameterisation are valid. The O3 response to changes in CH4 abundance is slightly larger in TF-HTAP Phase 2 than in the TF-HTAP Phase 1 assessment (2010) and provides further evidence that controlling CH4 is important for limiting future O3 concentrations. Different treatments of chemistry and meteorology in models remains one of the largest uncertainties in calculating the O3 response to perturbations in CH4 abundance and precursor emissions, particularly over the Middle East and South Asian regions. Emission changes for the future ECLIPSE scenarios and a subset of preliminary Shared Socio-economic Pathways (SSPs) indicate that surface O3 concentrations will increase by 1 to 8 ppbv in 2050 across different regions. Source attribution analysis highlights the growing importance of CH4 in the future under current legislation. A global tropospheric O3 radiative forcing of +0.07 W m−2 from 2010 to 2050 is predicted using the ECLIPSE scenarios and SSPs, based solely on changes in CH4 abundance and tropospheric O3 precursor emissions and neglecting any influence of climate change. Current legislation is shown to be inadequate in limiting the future degradation of surface ozone air quality and enhancement of near-term climate warming. More stringent future emission controls provide a large reduction in both surface O3 concentrations and O3 radiative forcing. The parameterisation provides a simple tool to highlight the different impacts and associated uncertainties of local and hemispheric emission control strategies on both surface air quality and the near-term climate forcing by tropospheric O3.

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