Constraints on global aerosol number concentration, SO<sub>2</sub> and condensation sink in UKESM1 using ATom measurements
<p>Understanding the vertical distribution of aerosol helps to reduce the uncertainty in the aerosol life cycle and therefore in the estimation of the direct and indirect aerosol forcing. To improve our understanding, we use measurements from four deployments of the Atmospheric Tomography (ATo...
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Copernicus Publications
2021-03-01
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Series: | Atmospheric Chemistry and Physics |
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record_format |
Article |
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DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
A. Ranjithkumar H. Gordon H. Gordon C. Williamson C. Williamson A. Rollins K. Pringle A. Kupc A. Kupc N. L. Abraham N. L. Abraham C. Brock K. Carslaw |
spellingShingle |
A. Ranjithkumar H. Gordon H. Gordon C. Williamson C. Williamson A. Rollins K. Pringle A. Kupc A. Kupc N. L. Abraham N. L. Abraham C. Brock K. Carslaw Constraints on global aerosol number concentration, SO<sub>2</sub> and condensation sink in UKESM1 using ATom measurements Atmospheric Chemistry and Physics |
author_facet |
A. Ranjithkumar H. Gordon H. Gordon C. Williamson C. Williamson A. Rollins K. Pringle A. Kupc A. Kupc N. L. Abraham N. L. Abraham C. Brock K. Carslaw |
author_sort |
A. Ranjithkumar |
title |
Constraints on global aerosol number concentration, SO<sub>2</sub> and condensation sink in UKESM1 using ATom measurements |
title_short |
Constraints on global aerosol number concentration, SO<sub>2</sub> and condensation sink in UKESM1 using ATom measurements |
title_full |
Constraints on global aerosol number concentration, SO<sub>2</sub> and condensation sink in UKESM1 using ATom measurements |
title_fullStr |
Constraints on global aerosol number concentration, SO<sub>2</sub> and condensation sink in UKESM1 using ATom measurements |
title_full_unstemmed |
Constraints on global aerosol number concentration, SO<sub>2</sub> and condensation sink in UKESM1 using ATom measurements |
title_sort |
constraints on global aerosol number concentration, so<sub>2</sub> and condensation sink in ukesm1 using atom measurements |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2021-03-01 |
description |
<p>Understanding the vertical distribution of aerosol helps to reduce the
uncertainty in the aerosol life cycle and therefore in the estimation of the direct and indirect aerosol forcing. To improve our understanding, we use
measurements from four deployments of the Atmospheric Tomography (ATom)
field campaign (ATom1–4) which systematically sampled aerosol and trace
gases over the Pacific and Atlantic oceans with near pole-to-pole coverage. We evaluate the UK Earth System Model (UKESM1) against ATom observations in terms of joint biases in the vertical profile of three variables related to
new particle formation: total particle number concentration (<span class="inline-formula"><i>N</i><sub>Total</sub></span>),
sulfur dioxide (SO<span class="inline-formula"><sub>2</sub></span>) mixing ratio and the condensation sink. The <span class="inline-formula"><i>N</i><sub>Total</sub></span>, SO<span class="inline-formula"><sub>2</sub></span> and condensation sink are interdependent quantities
and have a controlling influence on the vertical profile of each other; therefore, analysing them simultaneously helps to avoid getting the right
answer for the wrong reasons. The simulated condensation sink in the
baseline model is within a factor of 2 of observations, but the <span class="inline-formula"><i>N</i><sub>Total</sub></span>
and SO<span class="inline-formula"><sub>2</sub></span> show much larger biases mainly in the tropics and high
latitudes. We performed a series of model sensitivity tests to identify
atmospheric processes that have the strongest influence on overall model
performance. The perturbations take the form of global scaling factors or
improvements to the representation of atmospheric processes in the model,
for example by adding a new boundary layer nucleation scheme. In the
boundary layer (below 1 km altitude) and lower troposphere (1–4 km), inclusion of a boundary layer nucleation scheme
(Metzger et al., 2010) is critical to obtaining
better agreement with observations. However, in the mid (4–8 km) and upper
troposphere (<span class="inline-formula"><i>></i></span> 8 km), sub-3 nm particle growth, pH of cloud
droplets, dimethyl sulfide (DMS) emissions, upper-tropospheric nucleation rate, SO<span class="inline-formula"><sub>2</sub></span> gas-scavenging rate and cloud erosion rate play a more dominant role. We find that perturbations to boundary layer nucleation, sub-3 nm growth, cloud droplet pH and DMS emissions reduce the boundary layer and upper
tropospheric model bias simultaneously. In a combined simulation with all four perturbations, the SO<span class="inline-formula"><sub>2</sub></span> and condensation sink profiles are in much
better agreement with observations, but the <span class="inline-formula"><i>N</i><sub>Total</sub></span> profile still shows large deviations, which suggests a possible structural issue with how
nucleation or gas/particle transport or aerosol scavenging is handled in the
model. These perturbations are well-motivated in that they improve the
physical basis of the model and are suitable for implementation in future
versions of UKESM.</p> |
url |
https://acp.copernicus.org/articles/21/4979/2021/acp-21-4979-2021.pdf |
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doaj-31567a4f547e4c398a2195860c24c9392021-03-31T07:14:14ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242021-03-01214979501410.5194/acp-21-4979-2021Constraints on global aerosol number concentration, SO<sub>2</sub> and condensation sink in UKESM1 using ATom measurementsA. Ranjithkumar0H. Gordon1H. Gordon2C. Williamson3C. Williamson4A. Rollins5K. Pringle6A. Kupc7A. Kupc8N. L. Abraham9N. L. Abraham10C. Brock11K. Carslaw12School of Earth and Environment, University of Leeds, LS2 9JT, United KingdomSchool of Earth and Environment, University of Leeds, LS2 9JT, United KingdomEngineering Research Accelerator and Centre for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USACooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USANOAA Chemical Sciences Laboratory, Boulder, CO 80305, USACooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USASchool of Earth and Environment, University of Leeds, LS2 9JT, United KingdomNOAA Chemical Sciences Laboratory, Boulder, CO 80305, USAFaculty of Physics, Aerosol Physics and Environmental Physics, University of Vienna, 1090 Vienna, AustriaNCAS-Climate, University of Cambridge, CB2 1EW, UKDepartment of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UKNOAA Chemical Sciences Laboratory, Boulder, CO 80305, USASchool of Earth and Environment, University of Leeds, LS2 9JT, United Kingdom<p>Understanding the vertical distribution of aerosol helps to reduce the uncertainty in the aerosol life cycle and therefore in the estimation of the direct and indirect aerosol forcing. To improve our understanding, we use measurements from four deployments of the Atmospheric Tomography (ATom) field campaign (ATom1–4) which systematically sampled aerosol and trace gases over the Pacific and Atlantic oceans with near pole-to-pole coverage. We evaluate the UK Earth System Model (UKESM1) against ATom observations in terms of joint biases in the vertical profile of three variables related to new particle formation: total particle number concentration (<span class="inline-formula"><i>N</i><sub>Total</sub></span>), sulfur dioxide (SO<span class="inline-formula"><sub>2</sub></span>) mixing ratio and the condensation sink. The <span class="inline-formula"><i>N</i><sub>Total</sub></span>, SO<span class="inline-formula"><sub>2</sub></span> and condensation sink are interdependent quantities and have a controlling influence on the vertical profile of each other; therefore, analysing them simultaneously helps to avoid getting the right answer for the wrong reasons. The simulated condensation sink in the baseline model is within a factor of 2 of observations, but the <span class="inline-formula"><i>N</i><sub>Total</sub></span> and SO<span class="inline-formula"><sub>2</sub></span> show much larger biases mainly in the tropics and high latitudes. We performed a series of model sensitivity tests to identify atmospheric processes that have the strongest influence on overall model performance. The perturbations take the form of global scaling factors or improvements to the representation of atmospheric processes in the model, for example by adding a new boundary layer nucleation scheme. In the boundary layer (below 1 km altitude) and lower troposphere (1–4 km), inclusion of a boundary layer nucleation scheme (Metzger et al., 2010) is critical to obtaining better agreement with observations. However, in the mid (4–8 km) and upper troposphere (<span class="inline-formula"><i>></i></span> 8 km), sub-3 nm particle growth, pH of cloud droplets, dimethyl sulfide (DMS) emissions, upper-tropospheric nucleation rate, SO<span class="inline-formula"><sub>2</sub></span> gas-scavenging rate and cloud erosion rate play a more dominant role. We find that perturbations to boundary layer nucleation, sub-3 nm growth, cloud droplet pH and DMS emissions reduce the boundary layer and upper tropospheric model bias simultaneously. In a combined simulation with all four perturbations, the SO<span class="inline-formula"><sub>2</sub></span> and condensation sink profiles are in much better agreement with observations, but the <span class="inline-formula"><i>N</i><sub>Total</sub></span> profile still shows large deviations, which suggests a possible structural issue with how nucleation or gas/particle transport or aerosol scavenging is handled in the model. These perturbations are well-motivated in that they improve the physical basis of the model and are suitable for implementation in future versions of UKESM.</p>https://acp.copernicus.org/articles/21/4979/2021/acp-21-4979-2021.pdf |