Influence of Sea-Land Breezes on the Tempospatial Distribution of Atmospheric Aerosols over Coastal Region

ABSTRACT

The influence of sea-land breezes (SLBs) on the spatial distribution and temporal variation of particulate matter (PM) in the atmosphere was investigated over coastal Taiwan. PM was simultaneously sampled at inland and offshore locations during three intensive sampling periods. The intensive PM sampling protocol was continuously conducted over a 48-hr period. During this time, PM_2.5 and PM_2.5–10 (PM with aerodynamic diameters ≤2.5 μm and between 2.5 and 10 μm, respectively) were simultaneously measured with dichotomous samplers at four sites (two inland and two offshore sites) and PM₁₀ (PM with aerodynamic diameters ≤10 μm) was measured with β-ray monitors at these same 4 sites and at 10 sites of the Taiwan Air Quality Monitoring Network. PM sampling on a mobile air quality monitoring boat was further conducted along the coastline to collect offshore PM using a β-ray monitor and a dichotomous sampler. Data obtained from the inland sites (n = 12) and offshore sites (n = 2) were applied to plot the PM₁₀ concentration contour using Surfer software. This study also used a three-dimensional meteorological model (Pennsylvania State University/National Center for Atmospheric Research Meteorological Model 5) and the Comprehensive Air Quality Model with Extensions to simulate surface wind fields and spatial distribution of PM₁₀ over the coastal region during the intensive sampling periods. Spatial distribution of PM₁₀ concentration was further used in investigating the influence of SLBs on the transport of PM₁₀ over the coastal region. Field measurement and model simulation results showed that PM₁₀ was trans ported back and forth across the coastline. In particular, a high PM₁₀ concentration was observed at the inland sites during the day because of sea breezes, whereas a high PM₁₀ concentration was detected offshore at night because of land breezes. This study revealed that the accumulation of PM in the near-ocean region because of SLBs influenced the tempospatial distribution of PM₁₀ over the coastal region.

IMPLICATIONS

Model simulation and field measurements show that PM was transported back and forth across the coastline because of SLBs and that this regularly influenced the tempospatial distribution of PM₁₀ over the coastal region. A high PM₁₀ concentration was observed at the inland sites because of daytime onshore breezes, whereas a high PM₁₀concentration was detected over the ocean because of nighttime offshore breezes. The implications of these results suggest that relevant authorities should work to prevent pollution episodes by reducing regional PM emissions that lead to stagnant or recirculating air under specific weather conditions.