A shipborne micro-pulse lidar (Sigma Space Mini-MPL) was used to measure aerosol extinction coefficient over the northern region of the South China Sea from 9 August to 7 September 2016, the first time a mini-MPL was used for aerosol observation over the cruise region. The goal of the experiment was to investigate if the compact and affordable mini-MPL was usable for aerosol observation over this region. The measurements were used to calculate vertical profiles of volume extinction coefficient, depolarization ratio, and atmospheric boundary layer height. Aerosol optical depth (AOD) was lower over the southwest side of the cruise region, compared to the northeast side. Most attenuation occurred below 3.5 km, and maximum extinction values over coastal areas were generally about double of values offshore. The extinction coefficients at 532 nm (aerosol and molecular combined) over coastal and offshore areas were on average 0.04 km⁻¹ and 0.02 km⁻¹, respectively. Maximum values reached 0.2 km⁻¹ and 0.14 km⁻¹, respectively. Vertical profiles and back-trajectory calculations indicated vertical and horizontal layering of aerosols from different terrestrial sources. The mean volume depolarization ratio of the aerosols along the cruise was 0.04. The mean atmospheric boundary layer height along the cruise was 653 m, with a diurnal cycle reaching its mean maximum of 1041 m at 12:00 local time, and its mean minimum of 450 m at 20:00 local time. Unfortunately, only 11% of the measurements were usable. This was due to ship instability in rough cruise conditions, lack of stabilization rig, water condensation attached to the eye lens, and high humidity attenuating the echo signal. We recommend against the use of the mini-MPL in this cruise region unless substantial improvements are made to the default setup, e.g., instrument stabilization, instrument protection cover, and more theoretical work taking into account atmospheric gas scattering or absorption.

In this study, we evaluated the performance of an air pollution forecasting system during a scientific cruise in the South China Sea (SCS) from 9 August to 7 September 2016. The air pollution forecasting system consisted of a Lagrangian transport and dispersion model, the flexible particle dispersion model (FLEXPART), coupled with a high-resolution Weather Research and Forecasting model (WRF). The model system generally reproduced the meteorological variability and reasonably simulated the distribution of aerosols both vertically and horizontally along the cruise path. The forecasting system was further used to study the regional transport of non-local aerosols over the SCS and track its sources during the cruise. The model results showed that Southeast Asia contributed to more than 90% of the non-local aerosols over the northern region of the SCS due to the southwesterly prevailing winds. Specifically, the largest mean contribution was from Vietnam (39.6%), followed by Thailand (25.1%). This study indicates that the model system can be applied to study regional aerosols transport and provide air pollution forecasts in the SCS.

The South China Sea is the third largest inland sea in the world, with unique geographical and climatic conditions, and great economic importance. Observation of aerosols over this region is needed to understand their role in cloud, radiation, and ocean primary production. While the optical properties of marine aerosols over the South China Sea have been studied using solar photometers, there are no lidar studies for this region that the authors know of in publicly accessible scientific literature.To test the viability of shipborne lidar for aerosol measurement over the South China Sea, a shipborne micro-pulse lidar (Mini-MPL) was used to measure aerosol extinction coefficient in the northern region of the South China Sea over a period of one month from 9th August to 7th September, 2016, along the cruise path of a research vessel. The measurements were inverted to obtain vertical profiles of aerosol extinction coefficient, depolarization ratio, and atmospheric boundary layer height using Mie Theory and the Fernald method. Aerosols were found to be concentrated low in the atmosphere, with more than 73% of total extinction below 2 km and almost no aerosol above 3.5 km. Maximum extinction values in coastal areas were generally about double of values in offshore areas. The aerosol concentration was lower in the northwest side of the South China Sea compared to the northeast side, a pattern that may due to advection by the prevailing summer southwesterly winds. Vertical profiles and back-trajectory calculations indicated vertical and horizontal layering of aerosols from different terrestrial sources. The mean depolarization ratio of the aerosols along the cruise was 0.042. Atmospheric boundary layer height along the cruise was average 653.2 m, with a diurnal cycle reaching its mean maximum of 1041.2 m at 12:00, and its mean minimum of 450.0 m at 20:00.