The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West Africa
<p>Water in the atmosphere can exist in the solid, liquid or gas phase. At high humidities, if the aerosol population remains constant, more water vapour will condense onto the particles and cause them to swell, sometimes up to several times their original size. This significant change in size...
| Main Authors: | , , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-02-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/1505/2019/acp-19-1505-2019.pdf |
| _version_ | 1819262497096466432 |
|---|---|
| author | S. L. Haslett S. L. Haslett J. W. Taylor K. Deetz B. Vogel K. Babić N. Kalthoff A. Wieser C. Dione F. Lohou J. Brito R. Dupuy A. Schwarzenboeck P. Zieger P. Zieger H. Coe |
| author_facet | S. L. Haslett S. L. Haslett J. W. Taylor K. Deetz B. Vogel K. Babić N. Kalthoff A. Wieser C. Dione F. Lohou J. Brito R. Dupuy A. Schwarzenboeck P. Zieger P. Zieger H. Coe |
| author_sort | S. L. Haslett |
| collection | DOAJ |
| description | <p>Water in the atmosphere can exist in the solid, liquid or
gas phase. At high humidities, if the aerosol population remains constant,
more water vapour will condense onto the particles and cause them to swell,
sometimes up to several times their original size. This significant change in
size and chemical composition is termed hygroscopic growth and alters a
particle's optical properties. Even in unsaturated conditions, this can
change the aerosol direct effect, for example by increasing the extinction of
incoming sunlight. This can have an impact on a region's energy balance and
affect visibility. Here, aerosol and relative humidity measurements collected
from aircraft and radiosondes during the Dynamics–Aerosol–Chemistry–Cloud
Interactions in West Africa (DACCIWA) campaign were used to estimate the
effect of highly humid layers of air on aerosol optical properties during the
monsoon season in southern West Africa. The effects of hygroscopic growth in
this region are of particular interest due to the regular occurrence of high
humidity and the high levels of pollution in the region. The Zdanovskii,
Stokes and Robinson (ZSR) mixing rule is used to estimate the hygroscopic
growth of particles under different conditions based on chemical composition.
These results are used to estimate the aerosol optical depth (AOD) at
<span class="inline-formula"><i>λ</i>=525</span> nm for 63 relative humidity profiles. The median AOD in the
region from these calculations was 0.36, the same as that measured by sun
photometers at the ground site. The spread in the calculated AODs was less
than the spread from the sun photometer measurements. In both cases, values
above 0.5 were seen predominantly in the mornings and corresponded with high
humidities. Observations of modest variations in aerosol load and composition
are unable to explain the high and variable AODs observed using sun
photometers, which can only be recreated by accounting for the very elevated
and variable relative humidities (RHs) in the boundary layer. Most
importantly, the highest AODs present in the mornings are not possible
without the presence of high RH in excess of 95 %. Humid layers are found
to have the most significant impact on AOD when they reach RH greater than
98 %, which can result in a wet AOD more than 1.8 times the dry AOD.
Unsaturated humid layers were found to reach these high levels of RH in
37 % of observed cases. It can therefore be concluded that the high AODs
present across the region are driven by the high humidities and are then
moderated by changes in aerosol abundance. Aerosol concentrations in southern
West Africa are projected to increase substantially in the coming years;
results presented here show that the presence of highly humid layers in the
region is likely to enhance the consequent effect on AOD significantly.</p> |
| first_indexed | 2024-12-23T19:58:38Z |
| format | Article |
| id | doaj.art-cc4754c01bb04f56a82ed13715293a9d |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-23T19:58:38Z |
| publishDate | 2019-02-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-cc4754c01bb04f56a82ed13715293a9d2022-12-21T17:33:09ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242019-02-01191505152010.5194/acp-19-1505-2019The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West AfricaS. L. Haslett0S. L. Haslett1J. W. Taylor2K. Deetz3B. Vogel4K. Babić5N. Kalthoff6A. Wieser7C. Dione8F. Lohou9J. Brito10R. Dupuy11A. Schwarzenboeck12P. Zieger13P. Zieger14H. Coe15School of Earth and Environmental Sciences, University of Manchester, Manchester, UKnow at: Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, SwedenSchool of Earth and Environmental Sciences, University of Manchester, Manchester, UKInstitute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, GermanyInstitute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, GermanyInstitute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, GermanyInstitute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, GermanyInstitute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, GermanyLaboratoire d'Aérologie, Université Paul Sabatier Toulouse III (UPS), Toulouse, FranceLaboratoire d'Aérologie, Université Paul Sabatier Toulouse III (UPS), Toulouse, FranceLaboratoire de Météorologie Physique, Université Clermont Auvergne, Aubière, FranceLaboratoire de Météorologie Physique, Université Clermont Auvergne, Aubière, FranceLaboratoire de Météorologie Physique, Université Clermont Auvergne, Aubière, FranceDepartment of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, SwedenBolin Centre for Climate Research, Stockholm University, Stockholm, SwedenSchool of Earth and Environmental Sciences, University of Manchester, Manchester, UK<p>Water in the atmosphere can exist in the solid, liquid or gas phase. At high humidities, if the aerosol population remains constant, more water vapour will condense onto the particles and cause them to swell, sometimes up to several times their original size. This significant change in size and chemical composition is termed hygroscopic growth and alters a particle's optical properties. Even in unsaturated conditions, this can change the aerosol direct effect, for example by increasing the extinction of incoming sunlight. This can have an impact on a region's energy balance and affect visibility. Here, aerosol and relative humidity measurements collected from aircraft and radiosondes during the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) campaign were used to estimate the effect of highly humid layers of air on aerosol optical properties during the monsoon season in southern West Africa. The effects of hygroscopic growth in this region are of particular interest due to the regular occurrence of high humidity and the high levels of pollution in the region. The Zdanovskii, Stokes and Robinson (ZSR) mixing rule is used to estimate the hygroscopic growth of particles under different conditions based on chemical composition. These results are used to estimate the aerosol optical depth (AOD) at <span class="inline-formula"><i>λ</i>=525</span> nm for 63 relative humidity profiles. The median AOD in the region from these calculations was 0.36, the same as that measured by sun photometers at the ground site. The spread in the calculated AODs was less than the spread from the sun photometer measurements. In both cases, values above 0.5 were seen predominantly in the mornings and corresponded with high humidities. Observations of modest variations in aerosol load and composition are unable to explain the high and variable AODs observed using sun photometers, which can only be recreated by accounting for the very elevated and variable relative humidities (RHs) in the boundary layer. Most importantly, the highest AODs present in the mornings are not possible without the presence of high RH in excess of 95 %. Humid layers are found to have the most significant impact on AOD when they reach RH greater than 98 %, which can result in a wet AOD more than 1.8 times the dry AOD. Unsaturated humid layers were found to reach these high levels of RH in 37 % of observed cases. It can therefore be concluded that the high AODs present across the region are driven by the high humidities and are then moderated by changes in aerosol abundance. Aerosol concentrations in southern West Africa are projected to increase substantially in the coming years; results presented here show that the presence of highly humid layers in the region is likely to enhance the consequent effect on AOD significantly.</p>https://www.atmos-chem-phys.net/19/1505/2019/acp-19-1505-2019.pdf |
| spellingShingle | S. L. Haslett S. L. Haslett J. W. Taylor K. Deetz B. Vogel K. Babić N. Kalthoff A. Wieser C. Dione F. Lohou J. Brito R. Dupuy A. Schwarzenboeck P. Zieger P. Zieger H. Coe The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West Africa Atmospheric Chemistry and Physics |
| title | The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West Africa |
| title_full | The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West Africa |
| title_fullStr | The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West Africa |
| title_full_unstemmed | The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West Africa |
| title_short | The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southern West Africa |
| title_sort | radiative impact of out of cloud aerosol hygroscopic growth during the summer monsoon in southern west africa |
| url | https://www.atmos-chem-phys.net/19/1505/2019/acp-19-1505-2019.pdf |
| work_keys_str_mv | AT slhaslett theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT slhaslett theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT jwtaylor theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT kdeetz theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT bvogel theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT kbabic theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT nkalthoff theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT awieser theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT cdione theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT flohou theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT jbrito theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT rdupuy theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT aschwarzenboeck theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT pzieger theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT pzieger theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT hcoe theradiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT slhaslett radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT slhaslett radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT jwtaylor radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT kdeetz radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT bvogel radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT kbabic radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT nkalthoff radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT awieser radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT cdione radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT flohou radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT jbrito radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT rdupuy radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT aschwarzenboeck radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT pzieger radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT pzieger radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica AT hcoe radiativeimpactofoutofcloudaerosolhygroscopicgrowthduringthesummermonsooninsouthernwestafrica |