title: Investigating the nitrogen dioxide concentrations in the boundary layer by using multi-axis spectroscopic measurements and comparison with satellite observations.
abstract: This study emphasizes on near surface observation of chemically active trace gases such as nitrogen dioxide (NO2) over Islamabad on a regular basis. Absorption spectroscopy using backscattered extraterrestrial light source technique was used to retrieve NO2differential slant column densities (dSCDs). Mini multi-axis-differential optical absorption spectroscopy (MAX-DOAS) instrument was used to perform ground-based measurements at Institute of Environmental Sciences and Engineering (IESE), National University of Sciences and Technology (NUST) Islamabad, Pakistan. Tropospheric vertical column densities (VCDs) of NO2were derived from measured dSCDs by using geometric air mass factor approach. A case study was conducted to identify the impact of different materials (glass, tinted glass, and acrylic sheet of various thicknesses used to cover the instrument) on the retrieval of dSCDs. Acrylic sheet of thickness 5 mm was found most viable option for casing material as it exhibited negligible impact in the visible wavelength range. Tropospheric NO2VCD derived from ground-based mini MAX-DOAS measurements exceeded two times the Pak-NEQS levels and showed a reasonable comparison (r2= 0.65, r = 0.81) with satellite observations (root mean square bias of 39 %) over Islamabad, Pakistan.
authors.affiliation: Institute of Environmental Sciences and Engineering (IESE), National University of Sciences and Technology (NUST), Sector H-12, 444000, Islamabad, Pakistan. fahim.khokhar@iese.nust.edu.pk.
authors.forename: Muhammad Fahim
authors.initials: MF
authors.lastname: Khokhar
authors.affiliation: Institute of Environmental Sciences and Engineering (IESE), National University of Sciences and Technology (NUST), Sector H-12, 444000, Islamabad, Pakistan.
authors.forename: Munazza
authors.initials: M
authors.lastname: Nisar
authors.affiliation: Institute of Environmental Sciences and Engineering (IESE), National University of Sciences and Technology (NUST), Sector H-12, 444000, Islamabad, Pakistan.
authors.forename: Asma
authors.initials: A
authors.lastname: Noreen
authors.affiliation: Faculty of Forestry, Universiti Putra Malaysia, Serdang, 43400, Selangor, Malaysia.
authors.forename: Waseem Razzaq
authors.initials: WR
authors.lastname: Khan
authors.affiliation: Faculty of Forestry, Universiti Putra Malaysia, Serdang, 43400, Selangor, Malaysia. kur.hakeem@gmail.com.|Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia. kur.hakeem@gmail.com.
authors.forename: Khalid Rehman
authors.initials: KR
authors.lastname: Hakeem
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods; D009585:Nitrogen Dioxide / Q000032:analysis*; D010126:Ozone / Q000032:analysis; D010154:Pakistan; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D000393:Air Pollutants; D010126:Ozone; D009585:Nitrogen Dioxide
keywords: Air quality; Mini MAX-DOAS; NO2; Pakistan; Spectroscopy