Two distinct ship emission profiles for organic-sulfate source apportionment of PM in sulfur emission control areas

Source apportionment quantitatively links pollution to its source but can be difficult to perform in areas like ports where emissions from shipping and other port-related activities are intrinsically linked. Here we present the analysis of aerosol chemical speciation monitor (ACSM) data using combined organic and sulfate ion positive matrix factorisation (PMF) during an intensive measurement campaign in Dublin Port. Two main types of ship emissions were identified by this technique: sulfate-rich (S-Ship) and organic-rich (O-Ship). The S-Ship emissions were attributed to heavy fuel oil use and are characterised by particles with standard V/Ni ratios from 2.7-3.9 and a large fraction of acidic sulfate aerosol. The O-Ship emissions were attributed to low-sulfur fuel types and were comprised mostly of organic aerosol (OA) with the V/Ni ratios ranging only from 0-2.3. O-Ship plumes occurred over 3 times more frequently than S-Ship plumes during the measurement period. A third minor ship emission factor (X-Ship) was resolved by PMF but not clearly attributable to any specific fuel type. Overall, ship plumes had PM1 concentrations in the range 4-252 μg m^-3, with extreme concentrations usually lasting for 5-35 min. Despite their short duration, shipping emission plumes were frequent and contributed to at least 28 % of PM1 (i.e. 14 % O-Ship, 12 % S-Ship, and 2 % X-Ship). Moreover, hydrocarbon-like organic aerosol (HOA) and black carbon could also originate, in part, from shipping-related activities such as ferry traffic and heavy-goods vehicles, suggesting that the overall contribution of shipping activity to ambient PM1 is likely higher, upwards of 47 %.