Recent trends in aerosol optical properties derived from AERONET measurements

Abstract

Abstract. The Aerosol Robotic Network (AERONET) has been providing high-quality retrievals of aerosol optical properties from the surface at worldwide locations for more than a decade. Many sites have continuous and consistent records for more than 10 years, which enables the investigation of long-term trends in aerosol properties at these locations. In this study, we present the results of a trend analysis at selected stations with long data records. In addition to commonly studied parameters such as aerosol optical depth (AOD) and Ångström exponent (AE), we also focus on inversion products including absorption aerosol optical depth (ABS), single-scattering albedo (SSA) and the absorption Ångström exponent (AAE). Level 2.0 quality assured data are the primary source. However, due to the scarcity of level 2.0 inversion products resulting from the strict AOD quality control threshold, we have also analyzed level 1.5 data, with some quality control screening to provide a reference for global results. Two statistical methods are used to detect and estimate the trend: the Mann–Kendall test associated with Sen's slope and linear least-squares fitting. The results of these statistical tests agree well in terms of the significance of the trend for the majority of the cases. The results indicate that Europe and North America experienced a uniform decrease in AOD, while significant (>90%) increases in these two parameters are found for North India and the Arabian Peninsula. The AE trends turn out to be different for North America and Europe, with increases for the former and decreases for the latter, suggesting opposite changes in fine/coarse-mode fraction. For level 2.0 inversion parameters, Beijing and Kanpur both experienced an increase in SSA. Beijing also shows a reduction in ABS, while the SSA increase for Kanpur is mainly due the increase in scattering aerosols. Increased absorption and reduced SSA are found at Solar_Village. At level 1.5, most European and North American sites also show positive SSA and negative ABS trends, although the data are more uncertain. The AAE trends are less spatially coherent due to large uncertainties, except for a robust increase at three sites in West Africa, which suggests a possible reduction in black carbon. Overall, the trends do not exhibit obvious seasonality for the majority of parameters and stations.

Analysis of Aerosol Properties in Beijing Based on Ground-Based Sun Photometer and Air Quality Monitoring Observations from 2005 to 2014

“…The result is similar to that suggested in [54], which showed an AOD decrease in the range of 2007 to 2010 that might be caused by the efforts made by Chinese government for the preparation of Olympic Games in 2008. The decreasing trend is also shown in [55] with level 2.0 products. During these three periods, the AOD in summer varied most significantly while the variations in other seasons were less significantly.…”

Insight into global trends in aerosol composition from 2005 to 2015 inferred from the OMI Ultraviolet Aerosol Index

“…Prior to regression, the data are aggregated to monthly mean values, and the monthly time series data are deseasonalized by subtracting the monthly mean for the period 2005-2015 to focus on the long-term trend. Deseasonalization is a recommended method to accurately calculate a long-term trend in a seasonally varying time series (Weatherhead et al, 1998(Weatherhead et al, , 2002Wilks, 2011) and is widely employed for the trend analysis of geophysical data including temperature, chemical species concentrations, relative humidity, cloud cover, and aerosol parameters (Reynolds and Reynolds, 1988;Prinn et al, 1992;Pelletier and Turcotte, 1997;Zhang et al, 1997;Dai, 2006;Norris and Wild, 2007;Hsu et al, 2012;Boys et al, 2014;Li et al, 2014;Ma et al, 2016). Each pixel is required to have data for at least 60 % of the time period before regression is performed.…”

Aerosol Optical and Microphysical Properties of Four Typical Sites of SONET in China Based on Remote Sensing Measurements

“…Remote sensing techniques, especially ground-based remote sensing, can overcome these problems [15,16]. Satellite remote sensing plays an important role in aerosol detection as it can obtain aerosol information (e.g., AOD) with global coverage, however, it's difficult to retrieve other properties like single scattering albedo (SSA) from satellite measurements [17,18]. Although the Ozone Monitoring Instrument (OMI) on the Aura satellite provides both AOD and SSA retrievals, their accuracies are quite low (~30% and 0.1 for AOD and SSA, respectively [19]) compared to ground-based retrievals, probably due to the impacts caused by uncertainties in surface albedo given that the surface information contributes largely to the measured radiance [20].…”