Carbon Monitoring Satellite (CarbonSat): assessment of scattering related atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; retrieval errors and first results on implications for inferring city CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; emissions