Exposure to black carbon in the inner harbour area

Abstract

Residents living on the Isla creek and in the surrounding areas have been expressing their concerns about the pollutant emissions particularly from the cruise liners at berth in the harbour at least since summer 2018. International NGOs have taken (random) spot measurements of inter alia ultra fine particles in the area. These spot measurements were widely reported in the media but are however of limited scientific significance. This project analyses data gathered over a year, for a pollutant, Black Carbon (BC) that is known for its negative repercussions on human health. This data was analysed for variability, source and drivers of BC concentrations in an urban setting, that is not prone to heavy traffic flows. 95,730 verified BC 5-minute averaged values out of a possible 123,551 were analysed, for a data collection rate of 77%. Significant seasonal fluctuations in BC levels were determined; concentration peaks in different seasons and exhibit decreased values in other seasons. The time-series analysis highlights frequent spikes in BC concentrations, predominantly affecting the 95th percentiles, particularly during winter. Box plots indicate that while daily median BC levels are generally below 5 μg/m3, there are numerous outliers, suggesting occasional high exposure events for residents. Polar plots reveal a correlation between elevated BC concentrations and wind directions from the northwest and west, implicating the Grand Harbour's shipping activities as a significant source of BC pollution. The generalised linear model (GLM) explains 31% of the variability in BC levels, with wind speed, wind direction, as well as the number of stationary and moving ships, being significant predictors. The findings emphasise that while the overall BC concentrations align with urban background levels, the frequent high-concentration episodes potentially pose health risks. Overall, this project underscores the impact of maritime activities on urban air quality and the necessity for continuous monitoring and advanced analytical methods to mitigate health risks associated with BC exposure.