63 On the Importance of Organic Mass for Global Cloud …
399
Fig. 63.3 Persistence times of CCN 0.2 in atmosphere at the observational sites. Black bars show
the persistence times computed based on the observations of CCN 0.2 , while the red and blue bars
correspond to those calculated based on the TM4-ECPL model simulations with and without organics, respectively. For each pair of bars, the solid bar corresponds to winter and the dashed bar to
summer
change of the CCN population and not on the CCN abundance. The effect of the
presence of organics on the CCN 0.2 persistence is found to vary among sites with
the most stricking changes in Cabauw, with higher persistence times without organics that are also closer to observations. In Hyytiälä also higher persistence times are
computed when taking into account the contribution of organics and are significantly
higher in summer than derived from observations. In addition, the summer-to-winter
ratio of the persistence times is found to be affected by the presence of organics in
particular at Hyytiälä, where, surprisingly, neglecting the organics the CCN 0.2 during winter is more persistent than during summer in agreement with observations,
while at the high altitude Alpine station of Jungfraujoch the opposite trend is found.
The larger persistence during summer than during winter found in the observations
at this station is better captured by the model when considering the contribution of
organics.
63.3 Conclusion
This global 3-dimensional modeling study has shown that the organic mass significantly affects the CCN number concentrations. The annual surface distribution
of the CCN 0.2 number concentration is typically reduced by 50–90%, however, in
environments without a significant amount of organics (i.e. Jungfraujoch) CCN 0.2
does not show noticeable sensitivity to organic mass. Finally, based on the calculated
persistence times of the CCN 0.2 in the atmosphere, the inclusion of organics to the
aerosol components does not significantly affect the dynamics of the CCN.
Question by Ulas Im:
What is the contribution of OA to the CCN over the tropospheric column?
Reply:
399
Fig. 63.3 Persistence times of CCN 0.2 in atmosphere at the observational sites. Black bars show
the persistence times computed based on the observations of CCN 0.2 , while the red and blue bars
correspond to those calculated based on the TM4-ECPL model simulations with and without organics, respectively. For each pair of bars, the solid bar corresponds to winter and the dashed bar to
summer
change of the CCN population and not on the CCN abundance. The effect of the
presence of organics on the CCN 0.2 persistence is found to vary among sites with
the most stricking changes in Cabauw, with higher persistence times without organics that are also closer to observations. In Hyytiälä also higher persistence times are
computed when taking into account the contribution of organics and are significantly
higher in summer than derived from observations. In addition, the summer-to-winter
ratio of the persistence times is found to be affected by the presence of organics in
particular at Hyytiälä, where, surprisingly, neglecting the organics the CCN 0.2 during winter is more persistent than during summer in agreement with observations,
while at the high altitude Alpine station of Jungfraujoch the opposite trend is found.
The larger persistence during summer than during winter found in the observations
at this station is better captured by the model when considering the contribution of
organics.
63.3 Conclusion
This global 3-dimensional modeling study has shown that the organic mass significantly affects the CCN number concentrations. The annual surface distribution
of the CCN 0.2 number concentration is typically reduced by 50–90%, however, in
environments without a significant amount of organics (i.e. Jungfraujoch) CCN 0.2
does not show noticeable sensitivity to organic mass. Finally, based on the calculated
persistence times of the CCN 0.2 in the atmosphere, the inclusion of organics to the
aerosol components does not significantly affect the dynamics of the CCN.
Question by Ulas Im:
What is the contribution of OA to the CCN over the tropospheric column?
Reply: