Contribution of airborne dust particles to HONO sources

Abstract. HONO is a major precursor for OH radicals in early mornings. Its formation has been mainly attributed to the heterogeneous hydrolysis of NO2 on surfaces such as soot, glass, mineral oxides and aerosol surfaces. In particular, dust events which are loaded with mineral oxide aerosols have been associated with higher HONO concentrations in the gas phase. In order to understand the mechanism of reactions related to this process, samples during dusty and non-dusty days were collected between October 2009 and April 2011. Based on HYSPLIT backward trajectories, data were divided between wind trajectories originating from Arabian or African deserts. In this study an increase of HONO levels was observed during dusty days. The increase in the acidic gas concentrations was accompanied by an increase in the PM nitrate and sulfate ion concentrations. During high relative humidity (African dusty days), it is proposed that the mechanism of NO2 hydrolysis predominates whereas during Arabian dusty days, where the air is relatively dry, a synergistic mechanism of adsorption and reaction between NO2 and SO2 on dust particles to produce HONO and sulfate in the particle phase is suggested. This study implies that the NOx reactivity on mineral oxide surfaces leads to a higher mixing level of OH. An increase in the sulfate forming capacity could account for the underestimation of sulfates in aerosols when the reactive uptake of SO2 alone is considered.

Download Full-text

Saharan Dust Records and Its Impact in the European Alps

Oxford Research Encyclopedia of Climate Science ◽

10.1093/acrefore/9780190228620.013.827 ◽

2021 ◽

Author(s):

Marion Greilinger ◽

Anne Kasper-Giebl

Keyword(s):

Mineral Dust ◽

Cloud Condensation Nuclei ◽

Ice Cores ◽

Atmospheric Particulate Matter ◽

Saharan Dust ◽

Cloud Formation ◽

Dust Particles ◽

European Alps ◽

Airborne Dust ◽

Dust Events

Mineral dust is one of the main natural sources of atmospheric particulate matter, with the Sahara being one of the most important source regions for the occurrence and deposition of mineral dust in Europe. The occurrence of dust events in the European Alps is documented via measurements of airborne dust and its deposits onto the glaciers. Dust events occur mainly in spring, summer, and early autumn. Dust layers are investigated in ice cores spanning the last millennium as well as in annual snow packs. They strongly affect the overall flux of dust-related compounds (e.g., calcium and magnesium), provide an alkaline input to wet deposition chemistry, and change the microbial abundance and diversity of the snow pack. Still airborne mineral dust particles can act as ice nuclei and cloud condensation nuclei, influencing the formation of cloud droplets and hence cloud formation and precipitation. Dust deposits on the snow lead to a darkening of the surface, referred to as “surface albedo reduction,” which influences the timing of the snowmelt and reduces the annual mass balance of glaciers, showing a direct link to glacier retreat as observed presently in a warming climate.

Download Full-text

Modeling atmospheric mineral aerosol chemistry to predict heterogeneous photooxidation of SO<sub>2</sub>

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-10001-2017 ◽

2017 ◽

Vol 17 (16) ◽

pp. 10001-10017 ◽

Cited By ~ 10

Author(s):

Zechen Yu ◽

Myoseon Jang ◽

Jiyeon Park

Keyword(s):

Gas Phase ◽

Mineral Dust ◽

Uv Light ◽

Full Range ◽

Dust Particles ◽

Oh Radicals ◽

Desorption Kinetics ◽

So2 Oxidation ◽

Photocatalytic Ability ◽

Sulfate Formation

Abstract. The photocatalytic ability of airborne mineral dust particles is known to heterogeneously promote SO2 oxidation, but prediction of this phenomenon is not fully taken into account by current models. In this study, the Atmospheric Mineral Aerosol Reaction (AMAR) model was developed to capture the influence of air-suspended mineral dust particles on sulfate formation in various environments. In the model, SO2 oxidation proceeds in three phases including the gas phase, the inorganic-salted aqueous phase (non-dust phase), and the dust phase. Dust chemistry is described as the absorption–desorption kinetics of SO2 and NOx (partitioning between the gas phase and the multilayer coated dust). The reaction of absorbed SO2 on dust particles occurs via two major paths: autoxidation of SO2 in open air and photocatalytic mechanisms under UV light. The kinetic mechanism of autoxidation was first leveraged using controlled indoor chamber data in the presence of Arizona Test Dust (ATD) particles without UV light, and then extended to photochemistry. With UV light, SO2 photooxidation was promoted by surface oxidants (OH radicals) that are generated via the photocatalysis of semiconducting metal oxides (electron–hole theory) of ATD particles. This photocatalytic rate constant was derived from the integration of the combinational product of the dust absorbance spectrum and wave-dependent actinic flux for the full range of wavelengths of the light source. The predicted concentrations of sulfate and nitrate using the AMAR model agreed well with outdoor chamber data that were produced under natural sunlight. For seven consecutive hours of photooxidation of SO2 in an outdoor chamber, dust chemistry at the low NOx level was attributed to 55 % of total sulfate (56 ppb SO2, 290 µg m−3 ATD, and NOx less than 5 ppb). At high NOx ( >  50 ppb of NOx with low hydrocarbons), sulfate formation was also greatly promoted by dust chemistry, but it was suppressed by the competition between NO2 and SO2, which both consume the dust-surface oxidants (OH radicals or ozone).

Download Full-text

Saharan dust intrusions over the northern Mediterranean region in the frame of EARLINET (2014–2017): Properties and impact in radiative forcing

10.5194/acp-2020-611 ◽

2020 ◽

Author(s):

Ourania Soupiona ◽

Alexandros Papayannis ◽

Panagiotis Kokkalis ◽

Romanos Foskinis ◽

Guadalupe Sánchez Hernández ◽

...

Keyword(s):

Radiative Forcing ◽

Saharan Dust ◽

High Spectral Resolution ◽

Dust Particles ◽

Airborne Dust ◽

Geometrical Properties ◽

Thermal Range ◽

Lidar Measurements ◽

Dust Events ◽

Saharan Dust Intrusions

Abstract. Remote sensing measurements of aerosols using depolarization Raman Lidar systems from 4 EARLINET (European Aerosol research Lidar Network) stations are used for a comprehensive analysis of Saharan dust events over the Mediterranean basin in the period 2014–2017. In this period, we selected to study 51 dust events regarding the geometrical, optical and microphysical properties of dust particles, classifying them and assessing their radiative forcing effect on the atmosphere. From West to East, the stations of Granada, Potenza, Athens and Limassol were selected as representative Mediterranean cities regularly affected by Saharan dust intrusions. Emphasis was given on lidar measurements in the visible (532 nm) and specifically on the consistency of the particle linear depolarization ratio (δp532), the extinction-to-backscatter lidar ratio (LR532) and the Aerosol Optical Thickness (AOT532) within the observed dust layers. We found mean δp532 values of 0.24 ± 0.05, 0.26 ± 0.06, 0.28 ± 0.05 and 0.28 ± 0.04, mean LR532 values of 52 ± 8 sr, 51 ± 9 sr, 52 ± 9 sr and 49 ± 6 sr, and mean AOT532 values of 0.40 ± 0.31, 0.11 ± 0.07, 0.12 ± 0.10 and 0.32 ± 0.17, for Granada, Potenza, Athens and Limassol, respectively. The mean layer thickness values were found to range from ~1700 to ~3400 m. Additionally, based also on a previous aerosol type classification scheme provided by airborne High Spectral Resolution Lidar (HSRL) observations and on air mass backward trajectory analysis, a clustering analysis was performed in order to identify the major mixing aerosol types over the studied area. Furthermore, a synergy of lidar measurements and modeling was used to deeply analyze the solar and thermal radiative forcing of airborne dust. In total, a cooling behavior in the solar range and a significantly lower heating behavior in the thermal range was estimated. Depending on the dust optical and geometrical properties, the load intensity and the solar zenith angle (SZA), the estimated solar radiative forcing values range from −59 to −22 W m−2 at the surface and from −24 to −1 W m−2 at the top of the atmosphere (TOA). Similarly, in the thermal spectral range these values range from +2 to +4 W m−2 for the surface and from +1 to +3 W m−2 for the TOA. Finally, the radiative forcing seems to be inversely proportional to the dust mixing ratio, since higher absolute values are estimated for less mixed dust layers.

Download Full-text

Saharan dust and giant quartz particle transport towards Iceland

Scientific Reports ◽

10.1038/s41598-021-91481-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

György Varga ◽

Pavla Dagsson-Walhauserová ◽

Fruzsina Gresina ◽

Agusta Helgadottir

Keyword(s):

Numerical Models ◽

Saharan Dust ◽

Atmospheric Environment ◽

The Arctic ◽

Dust Particles ◽

Atmospheric Flow ◽

Dust Transport ◽

Strong Winds ◽

Dust Events ◽

Local Dust

AbstractMineral dust emissions from Saharan sources have an impact on the atmospheric environment and sedimentary units in distant regions. Here, we present the first systematic observations of long-range Saharan dust transport towards Iceland. Fifteen Saharan dust episodes were identified to have occurred between 2008 and 2020 based on aerosol optical depth data, backward trajectories and numerical models. Icelandic samples from the local dust sources were compared with deposited dust from two severe Saharan dust events in terms of their granulometric and mineralogical characteristics. The episodes were associated with enhanced meridional atmospheric flow patterns driven by unusual meandering jets. Strong winds were able to carry large Saharan quartz particles (> 100 µm) towards Iceland. Our results confirm the atmospheric pathways of Saharan dust towards the Arctic, and identify new northward meridional long-ranged transport of giant dust particles from the Sahara, including the first evidence of their deposition in Iceland as previously predicted by models.

Download Full-text