Background: The impact of shipping emissions on urban agglomerations close to major ports and vessel routes is probably one of the lesser understood aspects of anthropogenic air pollution. Little research has been done providing a satisfactory comprehension of the relationship between primary pollutant emissions, secondary aerosols formation and resulting air quality.
Materials and methods: In this study, multi-year (2003-2007) ambient speciated PM(10) and PM(2.5) data collected at four strategic sampling locations around the Bay of Algeciras (southern Spain), and positive matrix factorisation model were used to identify major PM sources with particular attention paid to the quantification of total shipping emissions. The impact of the emissions from both the harbour of Algeciras and vessel traffic at the Western entrance of Mediterranean Sea (Strait of Gibraltar) were quantified. Ambient levels of V, Ni, La and Ce were used as markers to estimate PM emitted by shipping.
Results and discussion: Shipping emissions were characterised by La/Ce ratios between 0.6 and 0.8 and V/Ni ratios around 3 for both PM(10) and PM(2.5). In contrast, elevated La/Ce values (1-5) are attributable to emissions from refinery zeolitic fluid catalytic converter plant, and low average V/Ni values (around 1) result mainly from contamination from stainless steel plant emissions. The direct contribution from shipping in the Bay of Algeciras was estimated at 1.4-2.6 μg PM(10)/m(3) (3-7%) and 1.2-2.3 μg PM(2.5)/m(3) (5-10%). The total contribution from shipping (primary emissions + secondary sulphate aerosol formation) reached 4.7 μg PM(10)/m(3) (13%) and 4.1 μg PM(2.5)/m(3) (17%).