Spaceborne observations of low surface aerosol concentrations in the Stockholm region

Matthias Tesche,Paul Glantz,Christer Johansson

doi:10.3402/tellusb.v68.28951

Abstract

This article investigates the feasibility of using spaceborne observations of aerosol optical thickness (AOT) derived with the Moderate Resolution Imaging Spectroradiometer (MODIS) for monitoring of fine particulate matter (PM2.5) in an environment of low aerosol loading. Previous studies of the AOT-to-PM2.5 relationship benefit from the large range of observed values. The Stockholm region features a comprehensive network of ground-based monitoring stations that generally show PM2.5 values <20 µg m−3. MODIS AOT at 555 nm is usually <0.20 and in good agreement with ground-based sun photometer observations in this region. We use MODIS Collection 5 AOT data with a horizontal resolution of 10 km×10 km and ground-based in-situ PM2.5 observations to derive an AOT-to-PM2.5 relationship that can be used to estimate fields of PM2.5. This has been carried out with respect to the months from April to September of the period 2000–2013. Relative average absolute deviations of 33–55 % (mean of 45 %) are obtained between MODIS-retrieved and ground-based PM2.5. The root mean square error is 0.2159 µg m−3 between retrieved and measured PM2.5. From spaceborne lidar observations, it is found that elevated aerosol layers are generally sparse in the Stockholm region. This favours remote sensing of PM2.5 from space. The deviations found between measured and retrieved PM2.5 are mainly attributed to infrequent situations of inhomogeneous aerosol layering for which column-integrated observations cannot be connected to surface conditions. Using MODIS Collection 6 data with a resolution of 3 km×3 km in a case study actually gives far fewer results than the coarser Collection 5 product. This is explained by the complex geography of the Stockholm region with a coastline and an abundance of lakes, which seems to induce biases in the retrieval of AOT at higher spatial resolution.

Highlights

Exposure to particulate pollution is known to impact human health (Kunzli et al, 2000; Anderson et al, 2012)
We conclude that Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical thickness (AOT) agrees relatively well with AERONET observations in the Stockholm region even though the aerosol loading is usually very low
We investigate the use of MODIS Collection 6 data with a spatial resolution of 3 km)3 km for monitoring PM2.5 in the Stockholm region

Summary

Introduction

Exposure to particulate pollution is known to impact human health (Kunzli et al, 2000; Anderson et al, 2012). Zhang et al (2009) showed that PM2.5 as derived from AOT observations from space can be used to fill gaps in continental-scale air-quality monitoring networks This is only valid in the absence of clouds (Christopher and Gupta, 2010) and when the column-integrated observations are representative for surface conditions (Crumeyrolle et al, 2014). Information on relative humidity (RH) and the presence of elevated aerosol layers from atmospheric modelling have been successfully used to improve the relationship between AOT and PM2.5 (Liu et al, 2005; Van Donkelaar et al, 2006) This allows for a global assessment of air quality based on spaceborne AOT observations (Van Donkelaar et al, 2010; Boys et al, 2014). The problems that arise are discussed in detail by Paciorek and Liu (2009), Snider et al (2015) and Crumeyrolle et al (2014)

Results

Discussion

Conclusion