A new optical-based technique for real-time measurements of mineral dust concentration in PM<sub>10</sub> using a virtual impactor

Abstract

Abstract. Atmospheric mineral dust influences Earth's radiative budget, cloud formation, and lifetime; has adverse health effects; and affects air quality through the increase of regulatory PM10 concentrations, making its real-time quantification in the atmosphere of strategic importance. Only few near-real-time techniques can discriminate dust aerosol in PM10 samples and they are based on the dust chemical composition. The online determination of mineral dust using aerosol absorption photometers offers an interesting and competitive alternative but remains a difficult task to achieve. This is particularly challenging when dust is mixed with black carbon, which features a much higher mass absorption cross section. We build on previous work using filter photometers and present here for the first time a highly time-resolved online technique for quantification of mineral dust concentration by coupling a high-flow virtual impactor (VI) sampler that concentrates coarse particles with an aerosol absorption photometer (Aethalometer, model AE33). The absorption of concentrated dust particles is obtained by subtracting the absorption of the submicron (PM1) aerosol fraction from the absorption of the virtual impactor sample (VI-PM1 method). This real-time method for detecting desert dust was tested in the field for a period of 2 months (April and May 2016) at a regional background site of Cyprus, in the Eastern Mediterranean. Several intense desert mineral dust events were observed during the field campaign with dust concentration in PM10 up to 45 µg m−3. Mineral dust was present most of the time during the campaign with an average PM10 of about 8 µg m−3. Mineral dust absorption was most prominent at short wavelengths, yielding an average mass absorption cross section (MAC) of 0.24±0.01 m2 g−1 at 370 nm and an absorption Ångström exponent of 1.41±0.29. This MAC value can be used as a site-specific parameter for online determination of mineral dust concentration. The uncertainty of the proposed method is discussed by comparing and validating it with different methods.

Towards understanding the characteristics of new particle formation in the Eastern Mediterranean

“…On the one hand, it can suppress photochemical processes by scavenging reactive gases and condensable vapors (De Reus et al, 2000;Ndour et al, 2009). On the other hand, it can provide particles that can act as a site for heterogeneous photochemistry promoting the formation of gaseous OH radicals, which initiate the conversion of SO 2 to H 2 SO 4 (Dupart et al, 2012;Nie et al, 2014). However, a clear association between high dust loading and NPF was not found from the data set presented here.…”

Supplementary material to "Towards understanding the mechanisms of new particle formation in the Eastern Mediterranean"

“…The method proposed by Drinovec et al (2020) permits the calculation mineral dust concentrations with high time resolution using the following equation…”

“…, 1 is the absorption coefficient (at 370nm) measured by a second AE33 Aethalometer sampling through a PM1 sharp-cut cyclone, EF is the enhancement factor of the VI and MAC is the mass absorption cross section for dust. The last two coefficients were used as determined experimentally by Drinovec et al (2020) where additional information about the method and the instruments used can be found.…”

Towards understanding the mechanisms of new particle formation in the Eastern Mediterranean

“…Measurement dates with high dust loading were identified using the VI-PM1 online method proposed by Drinovec et al (2020). This method couples a high-flow virtual impactor (VI) sampler, which concentrates coarse particles, with an aerosol absorption photometer.…”