Ground-based measurements of HCHO during the LISTOS (2018) campaign

Ground-based in situ (Aerodyne QCL) and MAX-DOAS (SciGlob Pandora) measurements of HCHO at Westport, CT (41.1183° N, 73.3367° W) during the Long Island Sound tropospheric ozone study (LISTOS) from July 21 to September 4, 2018 are presented. Pandora data analysis include: (1) detailed evaluation of systematic uncertainty of HCHO slant column calculation as a function of DOAS fitting parameters, and (2) vertical volume mixing ratio profile inversion using real time algorithm. Near surface volume mixing ratios (vmr) derived from the Pandora MAX-DOAS measurements are compared to the HCHO surface volume mixing ratios measured by the in-situ instrument. Strong linear correlation between the near surface remote sensing HCHO vmr and in-situ surface vmr was observed during the cloud-free days (R²= 0.90, slope=0.96), with slightly lower correlation for the entire measurement period (R²= 0.79, slope= 0.87). HCHO mixing layer height was derived from the MAX-DOAS Pandora profile measurements and compared to the planetary boundary layer height calculated from ceilometer data (CL51).