Trend estimates of AERONET-observed and model-simulated AOTs between 1993 and 2013

Abstract

Recently, temporal changes in Aerosol Optical Thickness (AOT) have been investigated based on model simulations, satellite and ground-based observations. Most AOT trend studies used monthly or annual arithmetic means that discard details of the generally right-skewed AOT distributions. Potentially, such results can be biased by extreme values (including outliers). This study additionally uses percentiles (i.e., the lowest 5%, 25%, 50%, 75% and 95% of the monthly cumulative distributions fitted to Aerosol Robotic Network (AERONET)-observed and ECHAM/MESSy Atmospheric Chemistry (EMAC)-model simulated AOTs) that are less affected by outliers caused by measurement error, cloud contamination and occasional extreme aerosol events. Since the limited statistical representativeness of monthly percentiles and means can lead to bias, this study adopts the number of observations as a weighting factor, which improves the statistical robustness of trend estimates. By analyzing the aerosol composition of AERONET-observed and EMAC-simulated AOTs in selected regions of interest, we distinguish the dominant aerosol types and investigate the causes of regional AOT trends. The simulated and observed trends are generally consistent with a high correlation coefficient (R = 0.89) and small bias (slope +/- 2 sigma = 0.75 +/- 0.19). A significant decrease in EMAC-decomposed AOTs by water-soluble compounds and black carbon is found over the USA and the EU due to environmental regulation. In particular, a clear reversal in the AERONET AOT trend percentiles is found over the USA, probably related to the AOT diurnal cycle and the frequency of wildfires. In most of the selected regions of interest, EMAC-simulated trends are mainly attributed to the significant changes of the dominant aerosols; e.g., significant decrease in sea salt and water soluble compounds over Central America, increase in dust over Northern Africa and Middle East, and decrease in black carbon and organic carbon over Australia. (C) 2015 The Authors. Published by Elsevier Ltd

The Climatology of Australian Aerosol

“…Trends in aerosol loading over the period 1995-2009 were recently compiled by Yoon et al (2016) at 15 AERONET stations. They showed that fine-mode anthropogenic aerosol is decreasing over those countries with strict environmental regulations, and vice versa.…”

Characteristics of Aerosol Types in Beijing and the Associations with Air Pollution from 2004 to 2015

“…Additionally, different aerosol types originate from several sources with diverse physical and optical properties, and from various atmospheric impacts [6][7][8][9][10]. Each aerosol type has a different climatic effect due to their size and absorptive and scattering nature, such as dust particles having large sizes and sulfate aerosols having a scattering nature, whereas nitrate particles with small sizes have absorbing tendencies [7,8,[11][12][13][14][15][16]. Consequently, long-term measurements of aerosol optical properties and aerosol types at a large scale are necessary to interpret the aerosol climatic effect [17,18].…”

Earth’s Climate System

“…The association of human activity with the presence of tropospheric aerosols is well established from both ground-based (Jimenez et al 2009;Yoon et al 2016) and space-based observations (Streets et al 2013;Yoon et al 2014;He et al 2016;McLinden et al 2016). Yet, quantification of the RF of climate due to tropospheric aerosols continues to pose a scientific challenge due to the inability to precisely define numerical values of both the direct modulation of RF by anthropogenic aerosols (Myhre 2009;Kahn 2012;Bond et al 2013) and the changes in RF driven by the effect of aerosols on clouds (Morgan et al 2006;Carslaw et al 2013).…”