Observation and modeling the vertical variability of the single scattering properties during Arctic Haze

This study has been carried out under Polish-Norwegian Research Programme entitled 'Impact of absorbing aerosols on radiative forcing in the European Arctic'. The main objectives of this project are properties of the Arctic haze phenomenon occurring in polar regions during spring season due to advection of polluted air masses from Europe and Asia. Despite the fact of having a low level of local emission, recent studies proved that Arctic represents a region with a high radiative forcing level. A significant role of vertical stratification of Arctic haze has been proven with strong regards to the layers over 5 km, where up to 75 per cent of total radiative forcing were measured. The aim of this research was to develop a methodology to retrieve aerosol single scattering properties measured in high latitudes during the episodes of strong Arctic Haze. Hence, a prototype mini-nephelometer receiving data from three wavelengths at 90 degree scattering angle as well as AE-51 mini-aethalometer had been installed onboard of tethered balloon where the in-situ observations were made. The construction of prototype mini-nephelometer was necessary for providing a method of retrieving the impact of the particle distribution upon the aethalometer filter's surface and inside it. The synergy of the mentioned instruments enhanced by the CHM15k ceilometer (1064 nm) data is expected to fulfil the objective of this study. In addition, the data from ground-base remote sensing measurements and numerical simulations of vertical profiles with aerosol optical properties obtained from Navy Aerosol Analysis and Prediction System (NAAPS) as well as Global Environmental Multiscale – Air Quality (GEM-AQ) was collected. Subsequently all of data was compared to determine the compatibility of the measurements. Analysis of the long-term (2001-2006, 2011-2012) simulation by NAAPS model confirmed a strong seasonal variation of both, single scattering albedo and extinction coefficient, where the highest values were observed during springtime. Particularly, episode of Arctic haze occurs mostly in March-May with extreme events at the end of the period. The variability of extinction coefficient vertical distribution is diverse. In March the profile shows two aerosol layers, first one in range of 0-4 km, which is believed to contain particles from sea salt emission (max value 0.017 1/km), second is found between 5-9 km of altitude (max value 0.01 1/km) probably consisting of allochtonous aerosols. In May the impact of polluted surface layer drops, in consequence it spreads only to 1.5 km (max value 0.01 1/km) of altitude, instead of probable Arctic haze layer, which can be noticed between 2 and 9 km with maximum amount of 0.0085 1/km. In the particular time, values of single scattering albedo vertical profiles are in range of 0.89 (May) to 0.93 (March). Its distribution shows rather small fluctuation during spring season. However, some enhanced extinction properties exist near the surface, where lower values of single scattering albedo are observed. The vertical distribution of modeled optical properties are believed to be similar to those obtained from in-situ tethered balloon measurements.