Mid-to late-January saw the year’s first Calimas - dust storms in the Canary Islands region originating in the Sahara Desert. These were accompanied by Saharan dust transport events across the Canary Islands towards the North Atlantic. Wind and weather conditions can carry dust for thousands of miles before it finally settles on the surface, so it is important to accurately predict the direction of the plume. The Copernicus Atmosphere Monitoring Service (CAMS*) has been doing just that – accurately forecasting the movement of the Saharan dust transport and evaluating its contribution to aerosol optical depth and particulate matter concentrations as it moved from the Sahara towards the North Atlantic.

As dust moves through the atmosphere, some of it settles on the surface. This can have a range of consequences, not all of which are negative – phosphorous and other nutrients in the dust can help improve soil quality. However, the impact on human health can be severe, as the dust aggravates allergies and the reduced air quality exacerbates respiratory problems. Accurate forecasting of the movement and density of the dust transports gives authorities the opportunity to take steps to minimise the health risks.

With respect to the recent Saharan dust transport, the CAMS global and regional ensemble forecasts showed transport of the Saharan dust out to the North Atlantic, reaching as far as Iceland, with some recirculation towards the British Isles and North Sea in the days between 17-21 January. A second episode, with transport from the Sahara crossing southern Spain and Portugal on its way to the North Atlantic, began on 27 January.

One measure of air pollution is the amount of coarse particulate matter – or PM10 – in the air close to the Earth’s surface, another is aerosol optical depth (AOD) which is a measure of how much direct sunlight is blocked by dust and haze in the atmosphere. CAMS has been tracking both and, as confirmed by Aeronet observations, the CAMS forecasts of total AOD represented the event very well, including the longer-range transport.

In the Canary Islands, air quality was severely degraded for several days as a result of the dust storms, with high measured PM10 values. CAMS had been observing persistently high values of AOD and PM10 well in excess of 200 μg/m3 over the Canary Islands between 14-20 January and from 27 January into early February. The CAMS AOD forecasts accurately captured the timing and enhancement of the plumes measured at Santa Cruz de Tenerife and at Cabo da Roca, Portugal, for example (see below).
“These episodes of Saharan dust in the first few weeks of 2022 have severely degraded air quality in the Canary Islands and undergone long-range transport to the North Atlantic,” said CAMS Senior Scientist Mark Parrington. “Recent weather patterns mean that, apart from southern parts of Portugal and Spain, we haven’t yet seen large scale transport across Europe but it shows the accuracy of CAMS monitoring in anticipation of possible future episodes, which may have more direct impacts across the continent,” he added.

Produced every 12 hours, CAMS forecasts cover the emission, transport and deposition of dust. Local communities in the path of the dust transport can use this information, along with CAMS analyses, to take mitigating action. Growing desertification due to climate change is likely to result in more dust in the atmosphere in the future, so information like that provided by CAMS will be critical in evaluating the impact of dust on human health and in planning strategies to counteract it.

*CAMS is implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF) on behalf of the European Commission.