Abstract:
Formaldehyde (HCHO) is an organic carbonyl compound found abundantly in the atmosphere. It is formed as a byproduct in the degradation pathways of many VOCs. This study was specifically designed to monitor the HCHO concentrations in different parts of Pakistan. Mini MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) instrument was used for both stationary and mobile monitoring of HCHO. Long term continuous monitoring of HCHO was performed at IESE, NUST, Islamabad for a period of four years. Apart from that, mobile field campaigns in the megacities of Multan and Lahore were conducted. Also, HCHO concentration in various forest areas of Pakistan were measured to study the role forests in VOC production and consequent HCHO formation in the atmosphere. MAX-DOAS observations were used to measure the diurnal, daily and annual cycle of HCHO concentrations over IESE, Islamabad. The diurnal cycle showed a good correlation of 0.74 among HCHO concentrations and temperature data indicating that the concentration of HCHO increase with the increase in temperature. Moreover, the annual cycle showed highest concentration during summer followed by spring, autumn and winter. During field campaigns HCHO concentration was found to be maximum in the vicinity of Tea Garden, Shinkiari. It was observed that the concentration of HCHO in the forest areas was well below the threshold value of 83 ppbv given by World Health Organization (WHO). Field campaigns conducted in Multan and Lahore revealed that HCHO concentrations were comparatively higher than the forest areas and also exceeded the threshold value at some points. Furthermore, tropospheric HCHO VCDs derived from ground-based mini MAX-DOAS measurements were compared with satellite data obtained from Ozone Monitoring Instrument (OMI). The satellite data underestimated the ground-based HCHO MAX-DOAS observations.
