Overview of Aerosol Properties in the European Arctic in Spring 2019 Based on In Situ Measurements and Lidar Data

• Main Authors: Fieke Rader, Rita Traversi, Mirko Severi, Silvia Becagli, Kim-Janka Müller, Konstantina Nakoudi, Christoph Ritter
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Atmosphere
• Subjects: Arctic haze; aerosol measurements; aerosol properties; in situ aerosol measurements; aerosol remote sensing; lidar
• Online Access: https://www.mdpi.com/2073-4433/12/2/271

In this work, we analysed aerosol measurements from lidar and PM<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mn>10</mn></msub></semantics></math></inline-formula> samples around the European Arctic site of Ny-Ålesund during late winter–early spring 2019. Lidar observations above 700 m revealed time-independent values for the aerosol backscatter coefficient (<inline-formula>β<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">β</mi></semantics></math></inline-formula>), colour ratio (CR), linear particle depolarisation ratio (<inline-formula>δ<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">δ</mi></semantics></math></inline-formula>) and lidar ratio (LR) from January to April. In contrast to previous years, in 2019 the early springtime backscatter increase in the troposphere, linked to <i>Arctic haze</i>, was not observed. In situ nss-sulphate (nss-SO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mrow></mrow><mn>4</mn><mrow><mn>2</mn><mo>−</mo></mrow></msubsup></semantics></math></inline-formula>) concentration was measured both at a coastal (Gruvebadet) and a mountain (Zeppelin) station, a few kilometres apart. As we employed different measurement techniques at sites embedded in complex orography, we investigated their agreement. From the lidar perspective, the aerosol load (indicated by <inline-formula>β<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">β</mi></semantics></math></inline-formula>) above 700 m changed by less than a factor of 3.5. On the contrary, the daily nss-SO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mrow></mrow><mn>4</mn><mrow><mn>2</mn><mo>−</mo></mrow></msubsup></semantics></math></inline-formula> concentration erratically changed by a factor of 25 (from 0.1 to 2.5 ng m<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></semantics></math></inline-formula>) both at Gruvebadet and Zeppelin station, with the latter mostly lying above the boundary layer. Moreover, daily nss-SO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mrow></mrow><mn>4</mn><mrow><mn>2</mn><mo>−</mo></mrow></msubsup></semantics></math></inline-formula> concentration was remarkably variable (correlation about 0.7 between the sites), despite its long-range origin. However, on a seasonal average basis the in situ sites agreed very well. Therefore, it can be argued that nss-SO<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msubsup><mrow></mrow><mn>4</mn><mrow><mn>2</mn><mo>−</mo></mrow></msubsup></semantics></math></inline-formula> advection mainly takes place in the lowest free troposphere, while under complex orography it is mixed downwards by local boundary layer processes. Our study suggests that at Arctic sites with complex orography ground-based aerosol properties show higher temporal variability compared to the free troposphere. This implies that the comparison between remote sensing and in situ observations might be more reasonable on longer time scales, i.e., monthly and seasonal basis even for nearby sites.