Investigation of Aerosol Properties and Structures in Two Representative Meteorological Situations over the Vipava Valley Using Polarization Raman LiDAR

Longlong Wang,Luka Drinovec,Asta Gregorič,Samo Stanič,William Eichinger,Griša Močnik

doi:10.3390/atmos10030128

Abstract

Vipava valley in Slovenia is a representative hot-spot for complex mixtures of different aerosol types of both anthropogenic and natural origin. Aerosol loading distributions and optical properties were investigated using a two-wavelength polarization Raman LiDAR, which provided extinction coefficient, backscatter coefficient, depolarization ratio, backscatter Ångström exponent and LiDAR ratio profiles. Two different representative meteorological situations were investigated to explore the possibility of identifying aerosol types present in the valley. In the first case, we investigated the effect of strong downslope (Bora) wind on aerosol structures and characteristics. In addition to observing Kelvin–Helmholtz instability above the valley, at the height of the adjacent mountain ridge, we found new evidence for Bora-induced processes which inject soil dust aerosols into the free troposphere up to twice the height of the planetary boundary layer (PBL). In the second case, we investigated aerosol properties and distributions in stable weather conditions. From the observed stratified vertical aerosol structure and specific optical properties of different layers we identified predominant aerosol types in these layers.

Highlights

IntroductionThe Vipava valley, located in the southwestern part of Slovenia, about 30 km inlands from the Bay of Trieste in the Adriatic (Figure 1), represents a typical case of a complex Alpine terrain configuration
The Vipava valley, located in the southwestern part of Slovenia, about 30 km inlands from the Bay of Trieste in the Adriatic (Figure 1), represents a typical case of a complex Alpine terrain configuration.Due to the morphological structure of this region, characterized by a multitude of basin valleys surrounded by mountains, ventilation in these valleys is predominantly poor, which leads to the formation of strong vertical aerosol gradients in lower troposphere
One category (29 days) refers to calm and stable atmospheric conditions, which are often accompanied by elevated aerosol concentrations within the valley and stratified atmospheric structure

Summary

Introduction

The Vipava valley, located in the southwestern part of Slovenia, about 30 km inlands from the Bay of Trieste in the Adriatic (Figure 1), represents a typical case of a complex Alpine terrain configuration. Due to the morphological structure of this region, characterized by a multitude of basin valleys surrounded by mountains, ventilation in these valleys is predominantly poor, which leads to the formation of strong vertical aerosol gradients in lower troposphere. In stable atmospheric conditions within the lower troposphere, especially in the winter, local emissions of anthropogenic aerosols (biomass burning and traffic) cause the Vipava valley to become a local air pollution hot-spot [1]. As a part of the Mediterranean region, the area is frequently affected by long-range transport of Saharan dust from North Africa across the Mediterranean and the Adriatic Sea, as well as sea salt. To monitor spatial loading distribution of different aerosol types and to understand the effects of various aerosol sources, experimental data with sufficiently high temporal and spatial

Objectives

Methods

Results

Conclusion