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 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 (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 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 (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 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.

Mr. X and the Pacific

2018 ◽  
Author(s):  
Paul J. Heer
Keyword(s):  
Soviet Union ◽  
East Asia ◽  
Vietnam War ◽  
Korean War ◽  
The United States ◽  
The Soviet Union ◽  
The Pacific ◽  
The Us ◽  
The Korean War ◽  
The Impact

This book chronicles and assesses the little-known involvement of US diplomat George F. Kennan—renowned as an expert on the Soviet Union—in US policy toward East Asia, primarily in the early Cold War years. Kennan, with vital assistance from his deputy John Paton Davies, played pivotal roles in effecting the US withdrawal from the Chinese civil war and the redirection of American occupation policy in Japan, and in developing the “defensive perimeter” concept in the western Pacific. His influence, however, faded soon thereafter: he was less successful in warning against US security commitments in Korea and Indochina, and the impact of the Korean War ultimately eclipsed his strategic vision for US policy in East Asia. This was due in large part to Kennan’s inability to reconcile his judgment that the mainland of East Asia was strategically expendable to the United States with his belief that US prestige should not be compromised there. The book examines the subsequent evolution of Kennan’s thinking about East Asian issues—including his role as a prominent critic of US involvement in the Vietnam War—and the legacies of his engagement with the region.

The Impact of European and Chinese Soft Power on Regional and Global Governance

2007 ◽  
Author(s):  
SEBASTIAN BERSICK
Keyword(s):  
East Asia ◽  
Global Governance ◽  
Soft Power ◽  
Regional Security ◽  
The Us ◽  
The Usa ◽  
The Impact

This chapter returns to issues raised by other authors in this section: the contrast between European, Chinese, and US perceptions of hard and soft power in the contexts of regional and global governance. Taking the ASEM process as a case, it shows how Europeans and Asians have approached the interaction from different institutional perspectives. Despite this, it sees ASEM as a process that reflects, and promotes, the advance of regional institutionalism in East Asia, adding an important dimension to the Europe–China relationship. This is then contrasted with the US strategy of dual divergence: a divergent internal strategy that rejects institutionalism for managing regional security; and an external divergent strategy that rejects the building of shared and reciprocal institutions between the USA and Asia. The chapter concludes that Europe's ‘balancing by convergence’ strategy has advantages over the USA's ‘balancing by divergence’ strategy.

scholarly journals Aircraft observations of enhancement and depletion of black carbon mass in the springtime Arctic

2010 ◽  
Vol 10 (6) ◽  
pp. 15167-15196
Author(s):  
J. R. Spackman ◽  
R. S. Gao ◽  
W. D. Neff ◽  
J. P. Schwarz ◽  
L. A. Watts ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Biomass Burning ◽  
Boundary Layer Transition ◽  
Arctic Climate ◽  
The Arctic ◽  
Vertical Profiles ◽  
Free Troposphere ◽  
Air Mass ◽  
The Impact

Abstract. Understanding the processes controlling black carbon (BC) in the Arctic is crucial for evaluating the impact of anthropogenic and natural sources of BC on Arctic climate. Vertical profiles of BC mass were observed from the surface to near 7-km altitude in April 2008 using a Single-Particle Soot Photometer (SP2) during flights on the NOAA WP-3D research aircraft from Fairbanks, Alaska. These measurements were conducted during the NOAA-sponsored Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project as part of POLARCAT, an International Polar Year (IPY) activity. In the free troposphere, the Arctic air mass was influenced by long-range transport from biomass-burning and anthropogenic source regions at lower latitudes especially during the latter part of the campaign. Maximum average BC mass loadings of 150 ng kg−1 were observed near 5.5-km altitude in the aged Arctic air mass. In biomass-burning plumes, BC was enhanced from near the top of the Arctic boundary layer (ABL) to 5.5 km compared to the aged Arctic air mass. At the bottom of some of the profiles, positive vertical gradients in BC were observed in the vicinity of open leads in the sea-ice. BC mass loadings increased by about a factor of two across the boundary layer transition in the ABL in these cases while carbon monoxide (CO) remained constant, evidence for depletion of BC in the ABL. BC mass loadings were positively correlated with O3 in ozone depletion events (ODEs) for all the observations in the ABL suggesting that BC was removed by dry deposition of BC on the snow or ice because molecular bromine, Br2, which photolyzes and catalytically destroys O3, is thought to be released near the open leads in regions of ice formation. We estimate the deposition flux of BC mass to the snow using a box model constrained by the vertical profiles of BC in the ABL. The open leads may increase vertical mixing in the ABL and entrainment of pollution from the free troposphere possibly enhancing the deposition of BC to the snow.

scholarly journals Combined assimilation of IASI and MLS observations to constrain tropospheric and stratospheric ozone in a global chemical transport model

2013 ◽  
Vol 13 (8) ◽  
pp. 21455-21505
Author(s):  
E. Emili ◽  
B. Barret ◽  
S. Massart ◽  
E. Le Flochmoen ◽  
A. Piacentini ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Transport Model ◽  
Stratospheric Ozone ◽  
Chemical Transport ◽  
Free Troposphere ◽  
Chemical Transport Model ◽  
Ozone Monitoring Instrument ◽  
Global Chemical Transport Model ◽  
The Impact

Abstract. Accurate and temporally resolved fields of free-troposphere ozone are of major importance to quantify the intercontinental transport of pollution and the ozone radiative forcing. In this study we examine the impact of assimilating ozone observations from the Microwave Limb Sounder (MLS) and the Infrared Atmospheric Sounding Interferometer (IASI) in a global chemical transport model (MOdèle de Chimie Atmosphérique à Grande Échelle, MOCAGE). The assimilation of the two instruments is performed by means of a variational algorithm (4-D-VAR) and allows to constrain stratospheric and tropospheric ozone simultaneously. The analysis is first computed for the months of August and November 2008 and validated against ozone-sondes measurements to verify the presence of observations and model biases. It is found that the IASI Tropospheric Ozone Column (TOC, 1000–225 hPa) should be bias-corrected prior to assimilation and MLS lowermost level (215 hPa) excluded from the analysis. Furthermore, a longer analysis of 6 months (July–August 2008) showed that the combined assimilation of MLS and IASI is able to globally reduce the uncertainty (Root Mean Square Error, RMSE) of the modeled ozone columns from 30% to 15% in the Upper-Troposphere/Lower-Stratosphere (UTLS, 70–225 hPa) and from 25% to 20% in the free troposphere. The positive effect of assimilating IASI tropospheric observations is very significant at low latitudes (30° S–30° N), whereas it is not demonstrated at higher latitudes. Results are confirmed by a comparison with additional ozone datasets like the Measurements of OZone and wAter vapour by aIrbus in-service airCraft (MOZAIC) data, the Ozone Monitoring Instrument (OMI) total ozone columns and several high-altitude surface measurements. Finally, the analysis is found to be little sensitive to the assimilation parameters and the model chemical scheme, due to the high frequency of satellite observations compared to the average life-time of free-troposphere/low-stratosphere ozone.

An Interdependence Theory of Wedge Strategies

2020 ◽  
Vol 13 (2) ◽  
pp. 253-286
Author(s):  
Yuxing Huang
Keyword(s):  
Soviet Union ◽  
East Asia ◽  
The United States ◽  
Great Power ◽  
Middle Power ◽  
The Soviet Union ◽  
Interdependence Theory ◽  
The Us ◽  
North Vietnam ◽  
The Impact

Abstract A wedge strategy is a state’s attempt to prevent, break up, or weaken a threatening or blocking alliance. An asymmetric alignment consists of a great power (the alignment leader) and a small/middle power (the weaker ally). So when does the wedge strategy of a great power (a divider) towards a competitive asymmetric alignment work? I propose, based upon the ‘Crawford–Izumikawa debate’, an ‘interdependence theory’ of wedge strategies. In the case of an asymmetric alignment that is symmetrically interdependent, the wedge strategy of a divider that accommodates the weaker ally is most likely to succeed. However, a wedge strategy towards an asymmetric alignment that is asymmetrically interdependent is highly likely to fail. I evaluate the theory based upon four wedge strategies adopted in Cold War Asia through analysing American, Russian, and Chinese archival sources. As asymmetrically interdependent, the US–Japan and US–Taiwan alliances offset the impact of Chinese wedge strategies. Between 1955 and 1965, therefore, neither Chinese accommodation nor Chinese pressure could detach weaker American allies from the United States in East Asia. However, China successfully exploited the symmetric interdependence of the US–Pakistan alliance. Between 1962 and 1965, China’s accommodation of Pakistan prevented Pakistan from being used as an American base for containment purposes. Likewise, the Soviet Union took full advantage of the Sino–Vietnamese alignment’s symmetric interdependence, whereby Soviet aid to North Vietnam caused rifts in Sino–Vietnamese relations that eventually wrecked the Sino–Vietnamese alignment. According to the theory, therefore, given the asymmetric interdependence of the hub-and-spokes system, any Chinese attempts to weaken US-sponsored alliances in East Asia would not be effective.

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