Abstract
Marine traffic in harbors can be responsible for significant atmospheric concentrations of ultrafine particles (UFPs), which have widely recognized negative effects on human health. It is therefore essential to model and measure the time evolution of the number size distributions and chemical composition of UFPs in ship exhaust to assess the resulting exposure in the vicinity of shipping routes. In this study, a sequential modelling chain was developed and applied, in combination with the data measured and collected in major harbor areas in the cities of Helsinki and Turku in Finland, during winter and summer in 2010–2011. The models described ship emissions, atmospheric dispersion, and aerosol dynamics, complemented with a time–microenvironment–activity model to estimate the short-term UFP exposure. We estimated the dilution ratio during the initial fast expansion of the exhaust plume to be approximately equal to eight. This dispersion regime resulted in a fully formed nucleation mode (denoted as Nuc2). Different selected modelling assumptions about the chemical composition of Nuc2 did not have an effect on the formation of nucleation mode particles. Aerosol model simulations of the dispersing ship plume also revealed a partially formed nucleation mode (Nuc1; peaking at 1.5 nm), consisting of freshly nucleated sulfate particles and condensed organics that were produced within the first few seconds. However, subsequent growth of the new particles was limited, due to efficient scavenging by the larger particles originating from the ship exhaust. The transport of UFPs downwind of the ship track increased the hourly mean UFP concentrations in the neighboring residential areas by a factor of two or more up to a distance of 3600 m, compared with the corresponding UFP concentrations in the urban background. The substantially increased UFP concentrations due to ship traffic significantly affected the daily mean exposures in residential areas located in the vicinity of the harbors.
Highlights
Large ships are primarily powered by diesel propulsion systems fueled by heavy fuel oil (HFO) [1].HFO is la ow-grade fuel, known as bunker oil or residual oil, which usually has a fuel sulfur content (FSC) of over 0.5% and includes a high concentration of impurities, such as ash, asphaltenes, Int
A sequential processing chain was developed in this study consisting of the 3-D chemistry transport model EPISODE-CityChem [33], the multicomponent aerosol dynamic model MAFOR [34,35], and a time–microenvironment–activity model, to assess the short-term population exposure to ultrafine particles originated from ship exhausts
This paper presented a sequential chain of models, which was used to simulate the temporal evolution of ultrafine particles
Summary
Large ships are primarily powered by diesel propulsion systems fueled by heavy fuel oil (HFO) [1].HFO is la ow-grade fuel, known as bunker oil or residual oil, which usually has a fuel sulfur content (FSC) of over 0.5% and includes a high concentration of impurities, such as ash, asphaltenes, Int. To model the dilution process, we assumed a circular cross-section of the plume. Time-dependent plume height, HP , was calculated as: The. HP (t) = (HP,0 2 + (a’·(10−3 ·Ut)b )2 ) 2 , (9). Where HP,0 is the initial plume height, corresponding to the height of the plume after the first dilution stage, here set to a value of 5.5 m [71]. The dilution parameter, b, is derived from the power-law fit to the empirical dilution curves. Parameter a’ relates to the vertical dispersion parameter, σz , of the Gaussian plume as a function of x (which is represented here in the form of the empirically determined power-law expression, σz = a’·xb ) and depends on the atmospheric stability and the averaging time.
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