THE RELATIONSHIP BETWEEN AFRICAN DUST AND PM10 CONCENTRATIONS AT CAYENNE, BARBADOS, AND GUADELOUPE: THE IMPLIED IMPACT ON AIR QUALITY IN THE CARIBBEAN BASIN AND NORTHERN SOUTH AMERICA

North Africa is the world's largest and most persistently active dust source, accounting for 70% of global emissions. A large fraction of these emissions is carried westward across the Atlantic in a "plume" that can be clearly seen in satellite products. The plume undergoes a seasonal progression that follows the changes in large-scale winds over the Atlantic; in summer to the Caribbean and southern United States; in spring, to the northeast coast of South America.

Here we report on multi-year unspeciated PM 10 measurements made at two sites as part of an official air quality program using certified instrumentation (TEOM): Cayenne, French Guiana (04.95, -52.31), and Pointe-á-Pitre, Guadeloupe (16.23, -61.53). These data are compared with daily speciated mineral aerosol measurements made concurrently on Barbados (13.17, -59.26). All station data show a strong seasonal cycle. At Guadeloupe, PM10 values peak in summer concurrently with dust peaks at Barbados, located 400 km SE, thus confirming the impact of African dust on PM10. At Guadeloupe, the 24 hour average PM10 met the WHO guideline (50 µg m^-3) on 216 days (total sample days 2480), all associated with dust events. At Cayenne, PM10 exceeded the guideline 301 days (total, 3206 days) all in late winter or spring, consistent with the presence of African dust. It is notable that spring PM10 values at Cayenne are very similar to summer PM10 at Guadeloupe and dust at Barbados which suggests that African dust transport continues unabated all year long.

There has been little research on the health impact of mineral dust associated with large scale natural dust events. This is especially true of PM10 events occurring at remote receptor sites – in our study, over 5000 km from the likely sources and requiring a transport time over a week during which time particle properties could change. A study of dust properties at distant sites is warranted along with health impact studies. Another concern is how dust concentrations – and PM10 – might change with changing climate. In the latest IPCC assessment, models project large changes in North Africa, some areas becoming much drier, but they do not agree on trends in large areas that are home to some of the most active dust sources today. Thus it is not possible to project PM10 trends – and any health impacts - in the future.