Over a 10-year record of aerosol optical properties at SMEAR II

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http://hdl.handle.net/10138/310900

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Luoma , K , Virkkula , A , Aalto , P , Petaja , T & Kulmala , M 2019 , ' Over a 10-year record of aerosol optical properties at SMEAR II ' , Atmospheric Chemistry and Physics , vol. 19 , no. 17 , pp. 11363-11382 . https://doi.org/10.5194/acp-19-11363-2019

Title: Over a 10-year record of aerosol optical properties at SMEAR II
Author: Luoma, Krista; Virkkula, Aki; Aalto, Pasi; Petaja, Tuukka; Kulmala, Markku
Contributor: University of Helsinki, INAR Physics
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
Date: 2019-09-09
Language: eng
Number of pages: 20
Belongs to series: Atmospheric Chemistry and Physics
ISSN: 1680-7316
URI: http://hdl.handle.net/10138/310900
Abstract: Aerosol optical properties (AOPs) describe the ability of aerosols to scatter and absorb radiation at different wavelengths. Since aerosol particles interact with the sun's radiation, they impact the climate. Our study focuses on the long-term trends and seasonal variations of different AOPs measured at a rural boreal forest site in northern Europe. To explain the observed variations in the AOPs, we also analyzed changes in the aerosol size distribution. AOPs of particles smaller than 10 mu m (PM10) and 1 mu m (PM1) have been measured at SMEAR II, in southern Finland, since 2006 and 2010, respectively. For PM10 particles, the median values of the scattering and absorption coefficients, single-scattering albedo, and backscatter fraction at lambda = 550 nm were 9.8 Mm(-1), 1.3 Mm(-1), 0.88, and 0.14. The median values of scattering and absorption angstrom ngstrom exponents at the wavelength ranges 450-700 and 370-950 nm were 1.88 and 0.99, respectively. We found statistically significant trends for the PM10 scattering and absorption coefficients, single-scattering albedo, and backscatter fraction, and the slopes of these trends were -0.32 Mm(-1), -0.086 Mm(-1), 2.2 x 10(-3), and 1.3 x 10(-3) per year. The tendency for the extensive AOPs to decrease correlated well with the decrease in aerosol number and volume concentrations. The tendency for the backscattering fraction and single-scattering albedo to increase indicates that the aerosol size distribution consists of fewer larger particles and that aerosols absorb less light than at the beginning of the measurements. The trends of the single-scattering albedo and backscattering fraction influenced the aerosol radiative forcing efficiency, indicating that the aerosol particles are scattering the radiation more effectively back into space.
Subject: LIGHT-ABSORPTION MEASUREMENTS
RADIATIVE PROPERTIES
BLACK CARBON
SEASONAL CYCLE
DECADAL TRENDS
VARIABILITY
AETHALOMETER
CLIMATE
ALBEDO
PARTICLES
114 Physical sciences
116 Chemical sciences
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