Spatiotemporal Trends of Aerosols over Urban Regions in Pakistan and Their Possible Links to Meteorological Parameters

Gohar Ali,Safi Ullah,Xulin Liu,Lin Li,Jun Ma,Yansong Bao,Qin Guan,Yuhong Lei,Waheed Ullah,Guangwen Li

doi:10.3390/atmos11030306

Abstract

Aerosol optical depth (AOD) has become one of the most crucial parameters for climate change assessment on regional and global scales. The present study investigates trends in AOD using long-term data derived from moderate resolution imaging spectro-radiometer (MODIS) over twelve regions in Pakistan. Different statistical tests are used to assess the annual and seasonal trends in AOD. Results reveal increasing AOD trends over most of the selected regions with an obvious increase over the north and northeastern parts of the study area. Annually, increasing trends (0.0002–0.0047 year−1) were observed over seven regions, with three being statistically significant. All the selected regions experience increasing AOD trends during the winter season with six being statistically significant while during the summer season seven regions experience increasing AOD trends and the remaining five exhibit the converse with two being statistically significant. The changes in the sign and magnitude of AOD trends have been attributed to prevailing meteorological conditions. The decreasing rainfall and increasing temperature trends mostly support the increasing AOD trend over the selected regions. The high/low AOD phases during the study period may be ascribed to the anomalies in mid-tropospheric relative humidity and wind fields. The summer season is generally characterized by high AOD with peak values observed over the regions located in central plains, which can be attributed to the dense population and enhanced concentration of industrial and vehicular emissions over this part of the study area. The results derived from the present study give an insight into aerosol trends and could form the basis for aerosol-induced climate change assessment over the study area.

Highlights

The direct and indirect effects of atmospheric aerosols on Earth’s climate system make them an integral part of the regional and global climate system [1,2,3]
moderate resolution imaging spectro-radiometer (MODIS) operates at an altitude of 705 km and makes radiance observations in 36 spectral channels in the wavelength range of 410–1440 nm at spatial resolution ranging from 250 m to 1 km with a 2300 km wide swath and almost daily global coverage
The non-parametric modified Mann–Kendall (m-MK) test was used to detect the significance of the trend, while the s slope (SS) estimator was used to determine the magnitude of the trend in Aerosol optical depth (AOD) time series

Summary

Introduction

The direct and indirect effects of atmospheric aerosols on Earth’s climate system make them an integral part of the regional and global climate system [1,2,3]. The cooling and heating effects of aerosols produced by backscattering and absorption of solar radiation respectively, are some of their adverse effects responsible for large scale mutation of the earth’s climate. Aerosols can indirectly influence the hydrological cycle, global surface temperature, and the ecosystems [4,5,6,7,8,9,10]. The scattering and absorption of dust particles modify the transmission of both short-wave and long-wave radiation through the atmosphere and heating the atmospheric column [11,12]. Aerosols are known to have detrimental effects on human health, air quality and visibility [13,14]

Methods

Results

Conclusion