Ship-plume sulfur chemistry: ITCT 2K2 case study.

Area of Science:

• Atmospheric Chemistry
• Marine Boundary Layer Dynamics
• Sulfur Biogeochemical Cycles

Background:

• Ship emissions significantly impact marine atmospheric chemistry.
• Understanding sulfur dioxide (SO2) transformation in ship plumes is vital for air quality and climate studies.
• The Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) experiment provided crucial data on ship-plume chemistry.

Purpose of the Study:

• To investigate ship-plume sulfur chemistry using a photochemical/dynamic model.
• To evaluate the model's performance by comparing predicted SO2 and H2SO4 with observed values.
• To estimate ship-plume SO2 lifetimes and identify key influencing factors.

Main Methods:

• Development and application of a ship-plume photochemical/dynamic model.
• Comparison of model-predicted mixing ratios of SO2 and H2SO4 with observational data from ITCT 2K2.
• Estimation of SO2 equivalent lifetimes (τ(eq)(SO(2))) under various marine boundary layer (MBL) conditions and sea-salt particle pH (pHss).

Main Results:

• Model predictions showed reasonable agreement with observations (0.56≤R≤0.71) when pHss ≤ ~6.5.
• Ship-plume SO2 lifetimes (τ(eq)(SO(2))) ranged from 10.32 to 14.32 hours, shorter than background SO2 lifetimes (15.18-23.20 hours).
• SO2 lifetime was primarily controlled by in-plume hydroxyl radical (OH) concentrations and pHss, with a shift in dominant loss processes based on pHss.

Conclusions:

• The model accurately simulates ship-plume sulfur chemistry under specific conditions.
• Sea-salt particle pH critically influences the dominant SO2 oxidation pathway: heterogeneous reactions with H2O2 or O3 at higher pH, and gas-phase OH oxidation at lower pH.
• Ship-plume SO2 is removed more efficiently than in the background atmosphere, impacting regional air quality and sulfur deposition.