Tropospheric NO<sub>2</sub>, SO<sub>2</sub>, and HCHO over the East China Sea, using ship-based MAX-DOAS observations and comparison with OMI and OMPS satellites data

Abstract

<p><strong>Abstract.</strong> In this study, ship-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were performed in the Eastern China Sea (ECS) area in June 2017. The tropospheric Slant Column Densities (SCDs) of nitrogen dioxide (NO<sub>2</sub>), sulfur dioxide (SO<sub>2</sub>), and formaldehyde (HCHO) were retrieved from the measured spectra by the Differential Optical Absorption Spectroscopy (DOAS) technique. Using the simple geometric approach, the SCDs of different trace gases observed at 15° elevation angle were adopted to convert into tropospheric Vertical Columns Densities (VCDs). During this campaign, the averaged VCDs of NO<sub>2</sub>, SO<sub>2</sub>, and HCHO in the marine environment over ECS area are 6.50 &times 10<sup>15</sup> molec cm<sup>−2</sup>, 4.28 &times 10<sup>15</sup> molec cm<sup>−2</sup> and 7.39 &times 10<sup>15</sup> molec cm<sup>−2</sup>, respectively. In addition, the ship-based MAX-DOAS trace gases VCDs were compared with satellite observations of Ozone Monitoring Instrument (OMI) and Ozone Mapping and Profiler Suite (OMPS). The daily OMI NO<sub>2</sub> VCDs agree well with ship-based MAX-DOAS measurements showing the correlation coefficient R of 0.83. Besides, the good agreements of SO<sub>2</sub> and HCHO VCDs between the OMPS satellite and ship-based MAX-DOAS observations were also found with correlation coefficient R of 0.76 and 0.69. The vertical profiles of these trace gases are achieved from the measured Differential Slant Column Densities (DSCDs) at different elevation angles using optimal estimation method. The retrieved profiles displayed the typical vertical distribution characteristics, which exhibits the low concentrations of < 3, < 3, and < 2 ppbv for NO<sub>2</sub>, SO<sub>2</sub>, and HCHO in clean area of the marine boundary layer far from coast of the Yangtze River Delta (YRD) continental region. Interestingly, elevated SO<sub>2</sub> concentrations can be observed intermittently along the ship routes, which is mainly attributed to the vicinal ship emissions in the view of the MAX-DOAS measurements. Combined with the on-board ozone lidar measurements, the ozone (O<sub>3</sub>) formation was discussed with the vertical profile of HCHO/NO<sub>2</sub> ratio, which is sensitive to the increases of NO<sub>2</sub> concentration. This study provided further understanding of the main air pollutants in the marine boundary layer of the ECS area and also benefited to formulate the policies regulating the shipping emissions in such costal area like YRD region.</p>

Detection of Outflow of Formaldehyde and Glyoxal from the African continent to the Atlantic Ocean with a MAX-DOAS Instrument

“…Also over the Pacific ocean enhanced HCHO columns were observed by Peters et al (2012) and Tan et al (2018). In both studies, HCHO was detected in elevated layer of 400 m and 500 m, which is lower than the detected altitudes in this study.…”

Surveillance of SO<sub>2</sub> and NO<sub>2</sub> from ship emissions by MAX-DOAS measurements and implication to compliance of fuel sulfur content

“…As an expanded apparatus, the multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements are high sensitivity to aerosols and trace gases in the lower troposphere by observing scattered sunlight under different viewing angles closed to the horizontal and the zenith directions (Hönninger et al, 2004;Ma et al, 2013;Sinreich et al, 2005;Wang et al, 2014). Due to its portability, MAX-DOAS instrument can be carried on the ship to observe the vertical column densities (VCDs) of NO2 and SO2 along the cruise, during which high levels of pollutants were found close to the busy port and dense lanes (Hong et al, 2018;Schreier et al, 2015;Takashima et al, 2012;Tan et al, 2018). In addition, MAX-DOAS has been successfully employed for monitoring shipping emissions directly.…”