Abstract:
The monitoring and analysis of formaldehyde (HCHO) column densities in urban
environments is crucial due to adverse impacts of trace gases on human health and the
environment. This study presents an in-depth investigation into the temporal
variability of HCHO column densities in Islamabad, Pakistan from 2015-2023.
Advanced ground-based instruments MAX-DOAS and NASA Pandora Spectrometer,
as well as satellite observations from OMI and TROPOMI instruments were used. The
study also presents a comprehensive analysis of meteorological parameters and their
role in tropospheric HCHO levels. Diurnal measurements of HCHO showed highest
levels during early morning and late evening hours due to the influence of
temperature, low solar radiation, and absence of radicals involved in atmospheric
chemical reactions. The seasonal cycle of HCHO showed higher levels during the
summer months, reaching a peak in June due to higher temperatures and resultant
biogenic emissions contributing to HCHO production. It was found to be the lowest in
winter owing to lower solar irradiance and temperature. Both OMI and TROPOMI
underestimated the ground-based HCHO observations due to their coarse spatial
resolution. In comparison with OMI, TROPOMI had a higher correlation of 0.79 and
0.71 for MAX-DOAS and Pandora respectively for HCHO vertical column densities
measured at the satellite overpass time. Comparisons between the two ground-based
instruments revealed nuanced discrepancies in measurements, highlighting the need
for rigorous intercomparison studies.
Keywords: HCHO, Temporal Variation, MAX-DOAS, NASA Pandora
Spectrometer, Air Quality.
