Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution?
Increases in free-tropospheric (FT) ozone based on ozonesonde records from the early 1990s through 2008 over two subtropical stations, Irene (near Pretoria, South Africa) and Réunion (21° S, 55° E; ~2800 km NE of Irene in the Indian Ocean), have been reported. Over Irene a large increase in the urba...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/9855/2014/acp-14-9855-2014.pdf |
| _version_ | 1818858541574782976 |
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| author | A. M. Thompson N. V. Balashov J. C. Witte J. G. R. Coetzee V. Thouret F. Posny |
| author_facet | A. M. Thompson N. V. Balashov J. C. Witte J. G. R. Coetzee V. Thouret F. Posny |
| author_sort | A. M. Thompson |
| collection | DOAJ |
| description | Increases in free-tropospheric (FT) ozone based on ozonesonde records from
the early 1990s through 2008 over two subtropical stations, Irene (near
Pretoria, South Africa) and Réunion (21° S, 55° E;
~2800 km NE of Irene in the Indian Ocean), have been reported. 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<sup>−1</sup>. 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 during the
Measurements of Ozone by Airbus In-service Aircraft (MOZAIC) project over
nearby Johannesburg. A multivariate regression model that accounts for the
annual ozone cycle, El Niño–Southern Oscillation (ENSO) and possible
tropopause changes was applied to monthly averaged Irene data from 4 to
11 km and to 1992–2011 Réunion sonde data from 4 to 15 km.
Statistically significant trends appear predominantly in the middle and upper
troposphere (UT; 4–11 km over Irene, 4–15 km over Réunion) in winter
(June–August), with increases ~1 ppbv yr<sup>−1</sup> over Irene and
~2 ppbv yr<sup>−1</sup> over Réunion. These changes are equivalent to
~25 and 35–45% decade<sup>−1</sup>, respectively. Both stations also
display smaller positive trends in summer, with a 45% decade<sup>−1</sup>
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 with 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
NO<sub>x</sub> emissions trends estimated for Africa, South America and
Madagascar. For Réunion trajectories also point to sources from the
eastern Indian Ocean and Asia. |
| first_indexed | 2024-12-19T08:57:56Z |
| format | Article |
| id | doaj.art-833482b27b7b405fbd31b005856c945f |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-19T08:57:56Z |
| publishDate | 2014-09-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-833482b27b7b405fbd31b005856c945f2022-12-21T20:28:34ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242014-09-0114189855986910.5194/acp-14-9855-2014Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution?A. M. Thompson0N. V. Balashov1J. C. Witte2J. G. R. Coetzee3V. Thouret4F. Posny5NASA/Goddard Space Flight Center, Code 614, Greenbelt, MD 20771, USAPennsylvania State University Dept. of Meteorology, University Park, PA 16802, USANASA/Goddard Space Flight Center, Code 614, Greenbelt, MD 20771, USASouth African Weather Service, Pretoria, South AfricaLaboratoire D'Aerologie, Obs. Du Midi-Pyrénées, Toulouse, FranceAtmosphere and Cyclone Lab, Université de La Réunion, La Réunion, FranceIncreases in free-tropospheric (FT) ozone based on ozonesonde records from the early 1990s through 2008 over two subtropical stations, Irene (near Pretoria, South Africa) and Réunion (21° S, 55° E; ~2800 km NE of Irene in the Indian Ocean), have been reported. 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<sup>−1</sup>. 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 during the Measurements of Ozone by Airbus In-service Aircraft (MOZAIC) project over nearby Johannesburg. A multivariate regression model that accounts for the annual ozone cycle, El Niño–Southern Oscillation (ENSO) and possible tropopause changes was applied to monthly averaged Irene data from 4 to 11 km and to 1992–2011 Réunion sonde data from 4 to 15 km. Statistically significant trends appear predominantly in the middle and upper troposphere (UT; 4–11 km over Irene, 4–15 km over Réunion) in winter (June–August), with increases ~1 ppbv yr<sup>−1</sup> over Irene and ~2 ppbv yr<sup>−1</sup> over Réunion. These changes are equivalent to ~25 and 35–45% decade<sup>−1</sup>, respectively. Both stations also display smaller positive trends in summer, with a 45% decade<sup>−1</sup> 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 with 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 NO<sub>x</sub> emissions trends estimated for Africa, South America and Madagascar. For Réunion trajectories also point to sources from the eastern Indian Ocean and Asia.http://www.atmos-chem-phys.net/14/9855/2014/acp-14-9855-2014.pdf |
| spellingShingle | A. M. Thompson N. V. Balashov J. C. Witte J. G. R. Coetzee V. Thouret F. Posny Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution? Atmospheric Chemistry and Physics |
| title | Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution? |
| title_full | Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution? |
| title_fullStr | Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution? |
| title_full_unstemmed | Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution? |
| title_short | Tropospheric ozone increases over the southern Africa region: bellwether for rapid growth in Southern Hemisphere pollution? |
| title_sort | tropospheric ozone increases over the southern africa region bellwether for rapid growth in southern hemisphere pollution |
| url | http://www.atmos-chem-phys.net/14/9855/2014/acp-14-9855-2014.pdf |
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