Effect of land–sea air mass transport on spatiotemporal distributions of atmospheric CO₂ and CH₄ mixing ratios over the southern Yellow Sea

<p>To reveal the spatiotemporal distributions of atmospheric CO<span class="inline-formula">₂</span> and CH<span class="inline-formula">₄</span> mixing ratios and regulation mechanisms over the China shelf sea, two field surveys were conducted in the southern Yellow Sea in China in November 2012 and June 2013, respectively. The results observed showed that mean background atmospheric CO<span class="inline-formula">₂</span> and CH<span class="inline-formula">₄</span> mixing ratios were 403.94 (<span class="inline-formula">±13.77</span>) ppm and 1924.8 (<span class="inline-formula">±27.8</span>) ppb in November 2012 and 395.90 (<span class="inline-formula">±3.53</span>) ppm and 1918.0 (<span class="inline-formula">±25.7</span>) ppb in June 2013, respectively. An improved data-filtering method was optimised and established to flag atmospheric CO<span class="inline-formula">₂</span> and CH<span class="inline-formula">₄</span> emission from different sources in the survey area. We found that the spatiotemporal distributions of atmospheric CO<span class="inline-formula">₂</span> and CH<span class="inline-formula">₄</span> mixing ratios over the southern Yellow Sea were dominated by land–sea air mass transport, which was mainly driven by seasonal monsoon, while the influence of air–sea exchange was negligible. In addition, atmospheric CO<span class="inline-formula">₂</span> and CH<span class="inline-formula">₄</span> mixing ratios over the southern Yellow Sea could be elevated remarkably at a distance of approximately 20 km offshore by land-to-sea air mass transportation from the Asian continent during the early-winter monsoon.</p>