Atmospheric Trace Gas (NO2 and O3) Variability in South Korean Coastal Waters, and Implications for Remote Sensing of Coastal Ocean Color Dynamics

Maria Tzortziou,Jay Herman,Nader Abuhassan,Lok Lamsal,Ryan Stauffer,Brian Lamb,Owen Parker

doi:10.3390/rs10101587

Abstract

Coastal environments are highly dynamic, and are characterized by short-term, local-scale variability in atmospheric and oceanic processes. Yet, high-frequency measurements of atmospheric composition, and particularly nitrogen dioxide (NO2) and ozone (O3) dynamics, are scarce over the ocean, introducing uncertainties in satellite retrievals of coastal ocean biogeochemistry and ecology. Combining measurements from different platforms, the Korea-US Ocean Color and Air Quality field campaign provided a unique opportunity to capture, for the first time, the strong spatial dynamics and diurnal variability in total column (TC) NO2 and O3 over the coastal waters of South Korea. Measurements were conducted using a shipboard Pandora Spectrometer Instrument specifically designed to collect accurate, high-frequency observations from a research vessel, and were combined with ground-based observations at coastal land sites, synoptic satellite imagery, and air-mass trajectory simulations to assess source contributions to atmospheric pollution over the coastal ocean. TCO3 showed only small (<20%) variability that was driven primarily by larger-scale meteorological processes captured successfully in the relatively coarse satellite imagery from Aura-OMI. In contrast, TCNO2 over the ocean varied by more than an order of magnitude (0.07–0.92 DU), mostly affected by urban emissions and highly dynamic air mass transport pathways. Diurnal patterns varied widely across the ocean domain, with TCNO2 in the coastal area of Geoje and offshore Seoul varying by more than 0.6 DU and 0.4 DU, respectively, over a period of less than 3 h. On a polar orbit, Aura-OMI is not capable of detecting these short-term changes in TCNO2. If unaccounted for in atmospheric correction retrievals of ocean color, the observed variability in TCNO2 would be misinterpreted as a change in ocean remote sensing reflectance, Rrs, by more than 80% and 40% at 412 and 443 nm, respectively, introducing a significant false variability in retrievals of coastal ocean ecological processes from space.

Highlights

At the interface between the land, oceans, and atmosphere, coastal regions are highly dynamic environments, characterized by strong variability in both water and air quality
It is essential for improved satellite trace gas retrievals, and for accurate atmospheric correction of satellite coastal ocean color observations, especially in coastal waters that are close to heavily polluted urban areas [2,10,11]
TCO3 varied by approximately 25% at each station, with most of this change captured by a quasi bi-weekly oscillation (13–15 days) that was clearly evident at all sites, and at Busan and Gwangju (Figure 2)

Summary

Introduction

At the interface between the land, oceans, and atmosphere, coastal regions are highly dynamic environments, characterized by strong variability in both water and air quality. Assessing the spatial and temporal variability of atmospheric pollutants, aerosols, and absorbing trace gases in coastal areas is critical for improving modeling and prediction of coastal tropospheric air quality, determining impacts on human health, and assessing the ecological implications of atmospheric pollutant deposition in coastal ecosystems [4]. It is essential for improved satellite trace gas retrievals, and for accurate atmospheric correction of satellite coastal ocean color observations, especially in coastal waters that are close to heavily polluted urban areas [2,10,11]. They can introduce a false diurnal variability in ocean retrievals from geostationary sensors such as GOCI [12,13]

Methods

Results

Conclusion