Temporal Variability and Characterization of Aerosols across the Pakistan Region during the Winter Fog Periods

Muhammad Khokhar,Naila Yasmin,Farrukh Chishtie,Imran Shahid

doi:10.3390/atmos7050067

Abstract

Fog is a meteorological/environmental phenomenon which happens across the Indo-Gangetic Plains (IGP) and leads to significant social and economic problems, especially posing significant threats to public health and causing disruptions in air and road traffic. Meteorological stations in Pakistan provide limited information regarding fog episodes as these provide only point observations. Continuous monitoring, as well as a spatially coherent picture of fog distribution, is possible through the use of satellite observations. This study focuses on the 2012–2015 winter fog episodes over the Pakistan region using the Moderate Resolution Image Spectrometer (MODIS), the Ozone Monitoring Instrument and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) products. The main objective of the study was to map the spatial distribution of aerosols, their types, and to identify the aerosol origins during special weather conditions like fog in Pakistan. The study also included ground monitoring of particulate matter (PM) concentrations, which were conducted during the 2014–2015 winter period only. Overall, this study is part of a multi-country project supported by the International Centre for Integrated Mountain Development (ICIMOD), started in 2014–2015 winter period, whereby scientists from Bangladesh, India and Nepal have also conducted measurements at their respective sites. A significant correlation between MODIS (AOD) and AERONET Station (AOD) data from Lahore was identified. Mass concentration of PM10 at all sampling sites within Lahore city exceeded the National Environmental Quality Standards (NEQS) levels on most of the occasions. Smoke and absorbing aerosol were found to be major constituents of winter fog in Pakistan. Furthermore, an extended span of winter fog was also observed in Lahore city during the winter of 2014–2015. The Vertical Feature Mask (VFM) provided by CALIPSO satellite confirmed the low-lying aerosol layers, instead of clouds for the vertical profiles of selected case studies.

Highlights

IntroductionAn increasing trend in fog frequencies over South Asia has been observed during the winter season for the last few decades, which has resulted in large disruptions in the daily lives of people across the region [1]
The study included ground monitoring of particulate matter (PM) concentrations, which were conducted during the 2014–2015 winter period only
This study is part of a multi-country project supported by the International Centre for Integrated Mountain Development (ICIMOD), started in 2014–2015 winter period, whereby scientists from Bangladesh, India and Nepal have conducted measurements at their respective sites

Summary

Introduction

An increasing trend in fog frequencies over South Asia has been observed during the winter season for the last few decades, which has resulted in large disruptions in the daily lives of people across the region [1]. Winter fog creates huge economic losses comparable to other extreme weather events such as hurricanes, storms, and tornadoes [2]. Clear sky, high moisture and stable atmospheric conditions are more suitable for fog formation [3,4]. Soil moisture is considered as an important factor in remote sensing for Atmosphere 2016, 7, 67; doi:10.3390/atmos7050067 www.mdpi.com/journal/atmosphere. Atmosphere 2016, 7, 67 fog monitoring [5]. In Pakistan, the Indus River and its tributaries along with soil moisture are considered as major sources air moisture and provide favourable conditions for fog formation

Objectives

Methods

Findings

Conclusion