INVESTIGATING THE DIURNAL AND WEEKLY CYCLE OF HCHO BY USING MINI MAX-DOAS OBSERVATIONS

Abstract

An oxygenated Volatile Organic Compound (VOC), Formaldehyde (HCHO), essentially contributes to the hazardous tropospheric ozone pollution in urban areas. Emissions from automobiles are the major contributors towards elevated formaldehyde concentrations in major urban cities of Pakistan, exposing the population to a polluted urban environment. This study was planned to quantify the formaldehyde concentration at a fixed place IESE, NUST Islamabad for a period of two years. Additionally, periodic mobile monitoring of HCHO was carried out with in cities of Lahore, Islamabad and Multan. Observations from MAX-DOAS (Multi-Axis – Differential Optical Absorption Spectroscopy) instrument was used to measure the diurnal, weekly and annual cycle in HCHO concentration at fixed site of Islamabad. The diurnal concentrations were found to increase with an increase in temperature. The weekly cycle revealed the higher values on working days and lesser values during the weekend, while the annual cycle shows the highest concentration in summer followed by spring, autumn and winter. During field campaigns the maximum mean values of HCHO over Lahore were found to be 164, 108, 283 ppb, meanwhile; the maximum mean value in Multan was 161 ppb, exceeding the limit prescribed by WHO (83 ppb). The suspected sources of HCHO at a fixed station and along routes of field campaigns were identified as natural gas consumption, biogenic emissions from vegetation, emissions from industries including brick kilns, steel mills, oil mills and vehicular emissions. Furthermore, monthly OMI satellite observations were compared with ground-based formaldehyde values. A good correlation of .68 was noticed within the time span of 6 am – 6 pm (PST).