Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site
<p>We present a comparison between three absorption photometers that measured the absorption coefficient (<span class="inline-formula"><i>σ</i><sub>abs</sub></span>) of ambient aerosol particles in 2012–2017 at SMEAR II (Station for Measuring Ecosy...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2021-10-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/14/6419/2021/amt-14-6419-2021.pdf |
| _version_ | 1819292317467541504 |
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| author | K. Luoma A. Virkkula P. Aalto K. Lehtipalo K. Lehtipalo T. Petäjä M. Kulmala |
| author_facet | K. Luoma A. Virkkula P. Aalto K. Lehtipalo K. Lehtipalo T. Petäjä M. Kulmala |
| author_sort | K. Luoma |
| collection | DOAJ |
| description | <p>We present a comparison between three absorption photometers that measured
the absorption coefficient (<span class="inline-formula"><i>σ</i><sub>abs</sub></span>) of ambient aerosol particles in
2012–2017 at SMEAR II (Station for Measuring Ecosystem–Atmosphere Relations II), a measurement station located in a boreal forest
in southern Finland. The comparison included an Aethalometer (AE31), a multi-angle absorption photometer (MAAP), and a particle soot absorption
photometer (PSAP). These optical instruments measured particles collected on
a filter, which is a source of systematic errors, since in addition to the
particles, the filter fibers also interact with light. To overcome this
problem, several algorithms have been suggested to correct the AE31 and PSAP
measurements. The aim of this study was to research how the different
correction algorithms affected the derived optical properties. We applied
the different correction algorithms to the AE31 and PSAP data and compared
the results against the reference measurements conducted by the MAAP. The
comparison between the MAAP and AE31 resulted in a multiple-scattering correction factor (<span class="inline-formula"><i>C</i><sub>ref</sub></span>) that is used in AE31 correction algorithms to
compensate for the light scattering by filter fibers. <span class="inline-formula"><i>C</i><sub>ref</sub></span> varies
between different environments, and our results are applicable to a boreal
environment. We observed a clear seasonal cycle in <span class="inline-formula"><i>C</i><sub>ref</sub></span>, which was
probably due to variations in aerosol optical properties, such as the
backscatter fraction and single-scattering albedo, and also due to
variations in the relative humidity (RH). The results showed that the
filter-based absorption photometers seemed to be rather sensitive to the
RH even if the RH was kept below the recommended value of 40 %. The
instruments correlated well (<span class="inline-formula"><i>R</i>≈0.98</span>), but the slopes of the
regression lines varied between the instruments and correction algorithms:
compared to the MAAP, the AE31 underestimated <span class="inline-formula"><i>σ</i><sub>abs</sub></span> only
slightly (the slopes varied between 0.96–1.00) and the PSAP overestimated
<span class="inline-formula"><i>σ</i><sub>abs</sub></span> only a little (the slopes varied between 1.01–1.04 for a
recommended filter transmittance <span class="inline-formula">>0.7</span>). The instruments and
correction algorithms had a notable influence on the absorption
Ångström exponent: the median absorption Ångström exponent
varied between 0.93–1.54 for the different algorithms and instruments.</p> |
| first_indexed | 2024-12-24T03:52:37Z |
| format | Article |
| id | doaj.art-1de26f2c04254441b9ff22c35a11e8b9 |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-24T03:52:37Z |
| publishDate | 2021-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-1de26f2c04254441b9ff22c35a11e8b92022-12-21T17:16:33ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482021-10-01146419644110.5194/amt-14-6419-2021Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest siteK. Luoma0A. Virkkula1P. Aalto2K. Lehtipalo3K. Lehtipalo4T. Petäjä5M. Kulmala6Institute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, 00014, FinlandAtmospheric Composition Research, Finnish Meteorological Institute, Helsinki, 00560, FinlandInstitute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, 00014, FinlandInstitute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, 00014, FinlandAtmospheric Composition Research, Finnish Meteorological Institute, Helsinki, 00560, FinlandInstitute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, 00014, FinlandInstitute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, 00014, Finland<p>We present a comparison between three absorption photometers that measured the absorption coefficient (<span class="inline-formula"><i>σ</i><sub>abs</sub></span>) of ambient aerosol particles in 2012–2017 at SMEAR II (Station for Measuring Ecosystem–Atmosphere Relations II), a measurement station located in a boreal forest in southern Finland. The comparison included an Aethalometer (AE31), a multi-angle absorption photometer (MAAP), and a particle soot absorption photometer (PSAP). These optical instruments measured particles collected on a filter, which is a source of systematic errors, since in addition to the particles, the filter fibers also interact with light. To overcome this problem, several algorithms have been suggested to correct the AE31 and PSAP measurements. The aim of this study was to research how the different correction algorithms affected the derived optical properties. We applied the different correction algorithms to the AE31 and PSAP data and compared the results against the reference measurements conducted by the MAAP. The comparison between the MAAP and AE31 resulted in a multiple-scattering correction factor (<span class="inline-formula"><i>C</i><sub>ref</sub></span>) that is used in AE31 correction algorithms to compensate for the light scattering by filter fibers. <span class="inline-formula"><i>C</i><sub>ref</sub></span> varies between different environments, and our results are applicable to a boreal environment. We observed a clear seasonal cycle in <span class="inline-formula"><i>C</i><sub>ref</sub></span>, which was probably due to variations in aerosol optical properties, such as the backscatter fraction and single-scattering albedo, and also due to variations in the relative humidity (RH). The results showed that the filter-based absorption photometers seemed to be rather sensitive to the RH even if the RH was kept below the recommended value of 40 %. The instruments correlated well (<span class="inline-formula"><i>R</i>≈0.98</span>), but the slopes of the regression lines varied between the instruments and correction algorithms: compared to the MAAP, the AE31 underestimated <span class="inline-formula"><i>σ</i><sub>abs</sub></span> only slightly (the slopes varied between 0.96–1.00) and the PSAP overestimated <span class="inline-formula"><i>σ</i><sub>abs</sub></span> only a little (the slopes varied between 1.01–1.04 for a recommended filter transmittance <span class="inline-formula">>0.7</span>). The instruments and correction algorithms had a notable influence on the absorption Ångström exponent: the median absorption Ångström exponent varied between 0.93–1.54 for the different algorithms and instruments.</p>https://amt.copernicus.org/articles/14/6419/2021/amt-14-6419-2021.pdf |
| spellingShingle | K. Luoma A. Virkkula P. Aalto K. Lehtipalo K. Lehtipalo T. Petäjä M. Kulmala Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site Atmospheric Measurement Techniques |
| title | Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site |
| title_full | Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site |
| title_fullStr | Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site |
| title_full_unstemmed | Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site |
| title_short | Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site |
| title_sort | effects of different correction algorithms on absorption coefficient a comparison of three optical absorption photometers at a boreal forest site |
| url | https://amt.copernicus.org/articles/14/6419/2021/amt-14-6419-2021.pdf |
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