Regional aerosol distribution and its long-range transport over the Indian Ocean

Abstract. The complex vertical distribution of aerosols over coastal southern West Africa (SWA) is investigated using airborne observations and numerical simulations. Observations were gathered on 2 July 2016 offshore of Ghana and Togo, during the field phase of the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa project. The aerosol loading in the lower troposphere includes emissions from coastal cities (Accra, Lomé, Cotonou and Lagos) as well as biomass burning aerosol and dust associated with long-range transport from Central Africa and the Sahara, respectively. Our results indicate that the aerosol distribution is impacted by subsidence associated with zonal and meridional regional scale overturning circulations associated with the land-sea surface temperature contrast and orography over Ghana and Togo. Numerical tracer release experiments highlight the dominance of aged emissions from Accra on the observed pollution plume loadings over the ocean. The contribution of aged emission from Lomé and Cotonou is also evident above the marine boundary layer. Lagos emissions do not play a role for the area west of Cotonou. The tracer plume does not extend very far south over the ocean (i.e. less than 100 km from Accra), mostly because emissions are transported northeastward near the surface over land and westward above the marine atmospheric boundary layer. The latter is possible due to interactions between the monsoon flow, complex terrain and land-sea breeze systems, which support the vertical mixing of the urban pollution. This work sheds light on the complex – and to date undocumented – mechanisms by which coastal shallow circulations distribute atmospheric pollutants over the densely populated SWA region.

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Apportioned contributions of PM 2.5 fine aerosol particles over the Maldives (northern Indian Ocean) from local sources vs long-range transport

The Science of The Total Environment ◽

10.1016/j.scitotenv.2015.07.059 ◽

2015 ◽

Vol 536 ◽

pp. 72-78 ◽

Cited By ~ 10

Author(s):

Krishnakant Budhavant ◽

August Andersson ◽

Carme Bosch ◽

Martin Kruså ◽

Ahmed Murthaza ◽

...

Keyword(s):

Indian Ocean ◽

Long Range ◽

Aerosol Particles ◽

Long Range Transport ◽

Northern Indian Ocean ◽

Pm 2.5 ◽

Fine Aerosol ◽

Range Transport ◽

Local Sources

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Aerosol distribution in the northern Gulf of Guinea: local anthropogenic sources, long-range transport, and the role of coastal shallow circulations

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-12363-2018 ◽

2018 ◽

Vol 18 (16) ◽

pp. 12363-12389 ◽

Cited By ~ 10

Author(s):

Cyrille Flamant ◽

Adrien Deroubaix ◽

Patrick Chazette ◽

Joel Brito ◽

Marco Gaetani ◽

...

Keyword(s):

Boundary Layer ◽

West Africa ◽

Long Range ◽

Anthropogenic Sources ◽

Long Range Transport ◽

Gulf Of Guinea ◽

General Direction ◽

Aerosol Distribution ◽

Range Transport ◽

Monsoon Flow

Abstract. The complex vertical distribution of aerosols over coastal southern West Africa (SWA) is investigated using airborne observations and numerical simulations. Observations were gathered on 2 July 2016 offshore of Ghana and Togo, during the field phase of the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa project. This was the only flight conducted over the ocean during which a downward-looking lidar was operational. The aerosol loading in the lower troposphere includes emissions from coastal cities (Accra, Lomé, Cotonou, and Lagos) as well as biomass burning aerosol and dust associated with long-range transport from central Africa and the Sahara, respectively. Our results indicate that the aerosol distribution on this day is impacted by subsidence associated with zonal and meridional regional-scale overturning circulations associated with the land–sea surface temperature contrast and orography over Ghana and Togo, as typically observed on hot, cloud-free summer days such as 2 July 2016. Furthermore, we show that the zonal circulation evidenced on 2 July is a persistent feature over the Gulf of Guinea during July 2016. Numerical tracer release experiments highlight the dominance of aged emissions from Accra on the observed pollution plume loadings over the ocean, in the area of aircraft operation. The contribution of aged emission from Lomé and Cotonou is also evident above the marine boundary layer. Given the general direction of the monsoon flow, the tracer experiments indicate no contribution from Lagos emissions to the atmospheric composition of the area west of Cotonou, where our airborne observations were gathered. The tracer plume does not extend very far south over the ocean (i.e. less than 100 km from Accra), mostly because emissions are transported northeastward near the surface over land and westward above the marine atmospheric boundary layer. The latter is possible due to interactions between the monsoon flow, complex terrain, and land–sea breeze systems, which support the vertical mixing of the urban pollution. This work sheds light on the complex – and to date undocumented – mechanisms by which coastal shallow circulations can distribute atmospheric pollutants over the densely populated SWA region.

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Simulation of Future Aerosol Distribution, Radiative Forcing, and Long-Range Transport in East Asia.

Journal of the Meteorological Society of Japan Ser II ◽

10.2151/jmsj.79.1139 ◽

2001 ◽

Vol 79 (6) ◽

pp. 1139-1155 ◽

Cited By ~ 23

Author(s):

Toshihiko Takemura ◽

Teruyuki Nakajima ◽

Toru Nozawa ◽

Kazuma Aoki

Keyword(s):

East Asia ◽

Long Range ◽

Radiative Forcing ◽

Long Range Transport ◽

Aerosol Distribution ◽

Range Transport

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Influence of Tropical Storms in the Northern Indian Ocean on Dust Entrainment and Long-Range Transport

Typhoon Impact and Crisis Management - Advances in Natural and Technological Hazards Research ◽

10.1007/978-3-642-40695-9_7 ◽

2014 ◽

pp. 149-174 ◽

Cited By ~ 4

Author(s):

V. Ramaswamy

Keyword(s):

Indian Ocean ◽

Long Range ◽

Long Range Transport ◽

Tropical Storms ◽

Northern Indian Ocean ◽

Range Transport ◽

Dust Entrainment

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Is tropospheric ozone over southern Africa really increasing? Evidence from sonde and aircraft profiles

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-10167-2014 ◽

2014 ◽

Vol 14 (7) ◽

pp. 10167-10207

Author(s):

A. M. Thompson ◽

N. V. Balashov ◽

J. C. Witte ◽

J. G. R. Coetzee ◽

V. Thouret ◽

...

Keyword(s):

Indian Ocean ◽

Tropospheric Ozone ◽

Multivariate Regression ◽

Early Morning ◽

Long Range Transport ◽

Gradual Change ◽

Multivariate Regression Model ◽

Upper Troposphere ◽

Range Transport ◽

The Indian Ocean

Abstract. Ozonesonde records from the early 1990's through 2008 over two subtropical stations, Irene (near Pretoria, South Africa) and Réunion Island (21° S, 55° W, ~3500 km NE of Irene in the Indian Ocean) were reported to exhibit free tropospheric (FT) ozone increases. Over Irene a large increase in the urban-influenced boundary layer (BL, 1.5–4 km) was also observed during the 18 year period, equivalent to 30% decade−1. Here we show that the Irene BL trend is at least partly due to a gradual change in the sonde launch times from early morning to the midday period. The FT ozone profiles over Irene in 1990–2007 are re-examined, filling in a 1995–1999 gap with ozone profiles taken by Measurements of Ozone by Airbus In-service Aircraft (MOZAIC) over nearby Johannesburg. A multivariate regression model that accounts for the annual ozone cycle, ENSO and possible tropopause changes was applied to monthly averaged Irene data from 4–11 km and to 1992–2011 Réunion sonde data from 4–15 km. Statistically significant trends appear predominantly in the middle and upper troposphere (UT, 4–11 km over Irene, 5–13 km over Réunion) in winter (June–August), with increases ~1 ppbv yr−1 over Irene and ~2 ppbv yr−1 over Réunion. These changes are equivalent to ~25% and 40–50% decade−1, respectively. Both stations also display smaller positive trends in summer with a 50% decade−1 ozone increase near the tropopause over Réunion in December. To explain the ozone increases, we investigated a time series of dynamical markers, e.g., potential vorticity (PV) at 330–350 K. PV affects UT ozone over Irene in November–December but displays little relationship to ozone over Réunion. A more likely reason for wintertime FT ozone increases over Irene and Réunion appears to be long-range transport of growing pollution in the Southern Hemisphere. The ozone increases are consistent with trajectory origins of air parcels sampled by the sondes and with recent NOx emissions trends estimated for Africa, South America, and Madagascar. For Réunion trajectories also point to pollution sources from the eastern Indian Ocean.

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