scholarly journals Impact of the isoprene photochemical cascade on tropical ozone

2012 ◽  
Vol 12 (3) ◽  
pp. 1307-1325 ◽  
Author(s):  
F. Paulot ◽  
D. K. Henze ◽  
P. O. Wennberg
Keyword(s):  
Boundary Layer ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Regional Scale ◽  
Oxidative Capacity ◽  
Adjoint Sensitivity ◽  
Tropical Regions ◽  
Isoprene Nitrates ◽  
Near Shore ◽  
Considerable Work

Abstract. Tropical tropospheric ozone affects Earth's radiative forcing and the oxidative capacity of the atmosphere. Considerable work has been devoted to the study of the processes controlling its budget. Yet, large discrepancies between simulated and observed tropical tropospheric ozone remain. Here, we characterize some of the mechanisms by which the photochemistry of isoprene impacts the budget of tropical ozone. At the regional scale, we use forward sensitivity simulation to explore the sensitivity to the representation of isoprene nitrates. We find that isoprene nitrates can account for up to 70% of the local NOx = NO+NO2 sink. The resulting modulation of ozone can be well characterized by their net modulation of NOx. We use adjoint sensitivity simulations to demonstrate that the oxidation of isoprene can affect ozone outside of continental regions through the transport of NOx over near-shore regions (e.g., South Atlantic) and the oxidation of isoprene outside of the boundary layer far from its emissions regions. The latter mechanism is promoted by the simulated low boundary-layer oxidative conditions. In our simulation, ~20% of the isoprene is oxidized above the boundary layer in the tropics. Changes in the interplay between regional and global effect are discussed in light of the forecasted increase in anthropogenic emissions in tropical regions.

scholarly journals Impact of the isoprene photochemical cascade on tropical ozone

2011 ◽  
Vol 11 (9) ◽  
pp. 25605-25654 ◽  
Author(s):  
F. Paulot ◽  
D. K. Henze ◽  
P. O. Wennberg
Keyword(s):  
Boundary Layer ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Regional Scale ◽  
Oxidative Capacity ◽  
Adjoint Sensitivity ◽  
Tropical Regions ◽  
Isoprene Nitrates ◽  
Near Shore ◽  
Considerable Work

Abstract. Tropical tropospheric ozone affects Earth's radiative forcing and the oxidative capacity of the atmosphere. Considerable work has been devoted to the study of the processes controlling its budget. Yet, large discrepancies between simulated and observed tropical tropospheric ozone remain. Here, we characterize some of the mechanisms by which the photochemistry of isoprene impacts the budget of tropical ozone. At the regional scale, we find that isoprene nitrates can account for up to 70% of the local NOx sink. Using forward sensitivity simulations, we show that the modulation of Ox by isoprene nitrates photochemistry can be characterized by their net impact on NOx. We use adjoint sensitivity simulations to demonstrate that the oxidation of isoprene can affect ozone outside of continental regions through the transport of NOx over near-shore regions (e.g., South Atlantic) and the oxidation of isoprene outside of the boundary layer far from its emissions regions. The latter mechanism is promoted by the simulated low boundary-layer oxidative conditions. In our simulation, ~20% of the isoprene is oxidized above the boundary layer in the tropics. Changes in the interplay between regional and global effect are discussed in light of the forecasted increase in anthropogenic emissions in tropical regions.

scholarly journals Simulations of Black Carbon Over Indian Region: Improvements and Implications of Diurnality in Emissions

2019 ◽  
Author(s):  
Gaurav Govardhan ◽  
Sreedharan Krishnakumari Satheesh ◽  
Krishnaswamy Krishna Moorthy ◽  
Ravi Nanjundiah
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Regional Scale ◽  
Early Morning ◽  
Temporal Variations ◽  
Indian Region ◽  
Near Surface ◽  
Aerosol Radiative Forcing ◽  
Convective Mixing

Abstract. With a view to improving the performance of WRF-Chem over the Indian region in simulating BC (black Carbon) mass concentrations as well as its short-term variations, especially on diurnal scale, a region-specific diurnal variation scheme has been introduced in the model emissios and the performance of the modified simulations has been evaluated against high-resolution measurements carried out over 8 ARFI (Aerosol Radiative Forcing over India) network observatories spread across India for distinct seasons; pre-monsoon (represented by May), post-monsoon (represented by October) and winter (represented by December). In addition to an overall improvement in the simulated concentrations and their temporal variations, it has also been found that the effects of prescribing diurnally varying emissions on the simulated near-surface concentrations largely depend on the boundary layer turbulence. The effects are perceived fast (within about 2–3 hours) during the evening–early morning hours when the atmospheric boundary layer is shallow and convective mixing is weak, while they are delayed, taking as much as about 5–6 hours, during periods when the boundary layer is deep and convective mixing is strong. This information would also serve as an important input for agencies concerned with urban planning and pollution mitigation. Despite these improvements in the near-surface concentrations, the simulated columnar aerosol optical depth (AOD) still remains largely underestimated vis-a-vis the satellite retrieved products. These modifications will serve as a guideline for further model-improvement initiatives at regional scale.

scholarly journals Simulations of black carbon over the Indian region: improvements and implications of diurnality in emissions

2019 ◽  
Vol 19 (12) ◽  
pp. 8229-8241 ◽  
Author(s):  
Gaurav Govardhan ◽  
Sreedharan Krishnakumari Satheesh ◽  
Krishnaswamy Krishna Moorthy ◽  
Ravi Nanjundiah
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Regional Scale ◽  
Early Morning ◽  
Temporal Variations ◽  
Indian Region ◽  
Near Surface ◽  
Aerosol Radiative Forcing ◽  
Convective Mixing

Abstract. With a view to improving the performance of WRF-Chem over the Indian region in simulating BC (black carbon) mass concentrations as well as its short-term variations, especially on a diurnal scale, a region-specific diurnal variation scheme has been introduced in the model emissions and the performance of the modified simulations has been evaluated against high-resolution measurements carried out over eight ARFI (Aerosol Radiative Forcing over India) network observatories spread across India for distinct seasons: pre-monsoon (represented by May), post-monsoon (represented by October) and winter (represented by December). In addition to an overall improvement in the simulated concentrations and their temporal variations, we have also found that the effects of prescribing diurnally varying emissions on the simulated near-surface concentrations largely depend on the boundary layer turbulence. The effects are perceived quickly (within about 2–3 h) during the evening–early morning hours when the atmospheric boundary layer is shallow and convective mixing is weak, while they are delayed, taking as much as about 5–6 h, during periods when the boundary layer is deep and convective mixing is strong. This information would also serve as an important input for agencies concerned with urban planning and pollution mitigation. Despite these improvements in the near-surface concentrations, the simulated columnar aerosol optical depth (AOD) still remains largely underestimated vis-à-vis the satellite-retrieved products. These modifications will serve as a guideline for further model-improvement initiatives at a regional scale.

scholarly journals The application of the Modified Band Approach for the calculation of on-line photodissociation rate constants in TM5: implications for oxidative capacity

2012 ◽  
Vol 5 (1) ◽  
pp. 15-35 ◽  
Author(s):  
J. E. Williams ◽  
A. Strunk ◽  
V. Huijnen ◽  
M. van Weele
Keyword(s):  
Boundary Layer ◽  
Rate Constants ◽  
Tropospheric Ozone ◽  
Transport Model ◽  
Chemical Species ◽  
Optimization Procedure ◽  
Oxidative Capacity ◽  
Boreal Winter ◽  
Middle Troposphere ◽  
On Line

Abstract. A flexible and explicit on-line parameterization for the calculation of tropospheric photodissociation rate constants (J-values) has been integrated into the global Chemistry Transport Model TM5. Here we provide a comprehensive description of this Modified Band Approach (MBA) including details of the optimization procedure employed, the methodology applied for calculating actinic fluxes, the photochemical reaction data used for each chemical species, the aerosol climatology which is adopted and the parameterizations adopted for improving the description of scattering and absorption by clouds. The resulting J-values change markedly throughout the troposphere when compared to the offline approach used to date, with significant increases in the boundary layer and upper troposphere. Conversely, for the middle troposphere a reduction in the actinic flux results in a decrease in J-values. Integrating effects shows that application of the MBA introduces seasonal dependent differences in important trace gas oxidants. Tropospheric ozone (O3) changes by ±10% in the seasonal mean mixing ratios throughout the troposphere, especially over land. These changes and the perturbations in the photolysis rate of O3 induce changes of ±15% in tropospheric OH. In part this is due to an increase in the re-cycling efficiency of nitrogen oxides. The overall increase in northern hemispheric tropospheric ozone strengthens the oxidizing capacity of the troposphere significantly and reduces the lifetime of CO and CH4 by ~5 % and ~4%, respectively. Changes in the tropospheric CO burden, however, are limited to a few percent due to competing effects. Comparing the distribution of tropospheric ozone in the boundary layer and middle troposphere against observations in Europe shows there are improvements in the model performance during boreal winter in the Northern Hemisphere near regions affected by high nitrogen oxide emissions. Monthly mean total columns of nitrogen dioxide and formaldehyde also compare more favorably against OMI and SCIAMACHY total column observations.

scholarly journals Global tropospheric ozone responses to reduced NOx emissions linked to the COVID-19 worldwide lockdowns

2021 ◽  
Vol 7 (24) ◽  
pp. eabf7460
Author(s):  
Kazuyuki Miyazaki ◽  
Kevin Bowman ◽  
Takashi Sekiya ◽  
Masayuki Takigawa ◽  
Jessica L. Neu ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Oxidative Capacity ◽  
Air Pollutant ◽  
Satellite Observations ◽  
Pollutant Emissions ◽  
Ozone Production ◽  
The Impact ◽  
Data Assimilation System ◽  
Assimilation System

Efforts to stem the transmission of coronavirus disease 2019 (COVID-19) led to rapid, global ancillary reductions in air pollutant emissions. Here, we quantify the impact on tropospheric ozone using a multiconstituent chemical data assimilation system. Anthropogenic NOx emissions dropped by at least 15% globally and 18 to 25% regionally in April and May 2020, which decreased free tropospheric ozone by up to 5 parts per billion, consistent with independent satellite observations. The global total tropospheric ozone burden declined by 6TgO3 (∼2%) in May and June 2020, largely due to emission reductions in Asia and the Americas that were amplified by regionally high ozone production efficiencies (up to 4 TgO3/TgN). Our results show that COVID-19 mitigation left a global atmospheric imprint that altered atmospheric oxidative capacity and climate radiative forcing, providing a test of the efficacy of NOx emissions controls for co-benefiting air quality and climate.

scholarly journals The Role of Plant CO2 Physiological Forcing in Shaping Future Daily-Scale Precipitation

2017 ◽  
Vol 30 (7) ◽  
pp. 2319-2340 ◽  
Author(s):  
Christopher B. Skinner ◽  
Christopher J. Poulsen ◽  
Robin Chadwick ◽  
Noah S. Diffenbaugh ◽  
Richard P. Fiorella
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Climate Models ◽  
Regional Scale ◽  
Heat Fluxes ◽  
Annual Number ◽  
Climate System Model ◽  
Precipitation Characteristics ◽  
Daily Scale ◽  
Precipitation Changes

Continued anthropogenic CO2 emissions are expected to drive widespread changes in precipitation characteristics. Nonetheless, projections of precipitation change vary considerably at the regional scale between climate models. Here, it is shown that the response of plant physiology to elevated CO2, or CO2 physiological forcing drives widespread hydrologic changes distinct from those associated with CO2 radiative forcing and has a role in shaping regional-scale differences in projected daily-scale precipitation changes. In a suite of simulations with the Community Climate System Model, version 4 (CCSM4), reduced stomatal conductance from projected physiological forcing drives large decreases in transpiration and changes the distribution of daily-scale precipitation within and adjacent to regions of dense vegetation and climatologically high transpiration. When atmospheric conditions are marginally favorable for precipitation, reduced transpiration dries the boundary layer and increases the likelihood of dry day occurrence. In CCSM4, the annual number of dry days increases by upward of 15 days yr−1 over tropical land and the continental midlatitudes. Decreases in transpiration from physiological forcing also increase the number of heavy precipitation events by up to 8 days yr−1 in many tropical forest regions. Despite reductions in the land surface contribution to atmospheric moisture, diminished surface latent heat fluxes warm the forest boundary layer and increase moisture convergence from nearby oceans, enhancing instability. The results suggest that consideration of the radiative impacts of CO2 alone cannot account for projected regional-scale differences in daily precipitation changes, and that CO2 physiological forcing may contribute to differences in projected precipitation characteristics among climate models.

scholarly journals The application of the Modified Band Approach for the calculation of on-line photodissociation rate constants in TM5: implications for oxidative capacity

2011 ◽  
Vol 4 (3) ◽  
pp. 2279-2325
Author(s):  
J. E. Williams ◽  
A. Strunk ◽  
V. Huijnen ◽  
M. van Weele
Keyword(s):  
Boundary Layer ◽  
Rate Constants ◽  
Tropospheric Ozone ◽  
Transport Model ◽  
Chemical Species ◽  
Optimization Procedure ◽  
Oxidative Capacity ◽  
Boreal Winter ◽  
Middle Troposphere ◽  
On Line

Abstract. A flexible and explicit on-line parameterization for the calculation of tropospheric photodissociation rate constants (J-values) has been integrated into the global Chemistry Transport Model TM5. Here we provide a comprehensive description of this Modified Band Approach (MBA) including details of the optimization procedure employed, the methodology applied for calculating actinic fluxes, the photochemical reaction data used for each chemical species and the parameterizations adopted for improving the description of scattering and absorption by clouds and aerosols. The resulting J-values change markedly throughout the troposphere when compared to the offline approach used to date, with significant increases in the boundary layer and upper troposphere. Conversely, for the middle troposphere a reduction in the actinic flux results in a decrease in J-values. Integrating effects shows that application of the MBA introduces seasonal dependent differences in important trace gas oxidants. Tropospheric ozone changes by ±5% in the seasonal mean mixing ratios throughout the troposphere, which induces changes of ±15% in tropospheric OH. In part this is due to an increase in the re-cycling efficiency of nitrogen oxides. The overall increase in northern hemispheric tropospheric ozone strengthens the oxidizing capacity of the troposphere significantly and reduces the lifetime of CO and CH4 by ~5% and ~4%, respectively. Changes in the tropospheric CO burden, however, are limited to a few percent due to competing effects. Comparing the distribution of tropospheric ozone in the boundary layer and middle troposphere against observations in Europe shows there are improvements in the model performance during boreal winter in the Northern Hemisphere near regions affected by high nitrogen oxide emissions. Monthly mean total columns of nitrogen dioxide and formaldehyde also compare more favorably against OMI and SCIAMACHY total column observations.

scholarly journals Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing

2017 ◽  
Author(s):  
Ben Newsome ◽  
Mat Evans
Keyword(s):  
Rate Constant ◽  
Atmospheric Chemistry ◽  
Rate Constants ◽  
Tropospheric Ozone ◽  
Radiative Forcing ◽  
Transport Model ◽  
Surface Ozone ◽  
Photolysis Rates ◽  
The Impact ◽  
Chemical Rate

Abstract. Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global use these rate constants. Expert panels synthesise laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the JPL and IUPAC evaluations we assess 50 mainly inorganic rate constants and 10 photolysis rates, through simulations where we increase the rate of the reactions to the 1σ upper value recommended by the expert panels. We assess the impact on 4 standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH    M →  HNO3, OH + CH4 → CH3O2 + H2O and O3 + NO → NO2 + O2 are the three largest source of uncertainty in these metrics. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions, gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 11, 12, 17 and 17 % respectively. These are larger than the spread between models in recent model inter-comparisons. Remote regions such as the tropics, poles, and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered when model results disagree with measurement. Calculations for the pre-industrial allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 Wm−2. This uncertainty (15 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model-model inter-comparison studies where the rate constants used in the models are all identical or very similar. Thus the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.

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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