Fig. 1.
Inlet system and instrumental setup during the CAEsAR campaign. PM10 refers to particulate matter with aerodynamic diameters smaller than 10 µm and CVI to counterflow virtual impactor, which were the two main aerosol inlets. DMPS refers to differential mobility particle sizer, VHTDMA to volatility and hygroscopicity tandem differential mobility analyser, measuring at the initial diameter (D init.), MAAP to multi-angle absorption photometer, measuring the black carbon (BC) content at the wavelength (λ), and EM to elemental mass (an estimate of BC derived from EC).
Fig. 2.
Overview of the ambient particle size distribution and chemical composition of PM10 and cloud water during the CAEsAR campaign. (a) Ambient size distribution measured behind the PM10 inlet; (b) and (c) the chemical composition of the analysed fraction of PM10 (inidicated by the black lines, see below) and cloud water, respectively. The analysed chemical composition is comprised of total organic mass (TOM, with water-soluble and water-insoluble OM for the liquid phase), elemental mass (EM) and inorganic mass (IM). The black lines represent the total mass concentrations inferred from the sum of analysed chemical species, and the purple line the total (sub-10 µm) PM mass inferred from the particle size distribution measurements assuming a particle density of 1500 kg m−3. Blue circles above panel (a) mark the times when the station engulfed in cloud and the CVI inlet was on. The red and blue lines below panel (c) mark the times when the VHTDMA was running in volatility and hygroscopicity mode, respectively.
Table 1.
Mean chemical composition (±standard deviation) of PM10 and cloud water, based on 37 and 16 samples collected during 2520 and 1682 h, respectively.
Fig. 3.
Median size distributions, with shaded areas presenting the quartiles, of the ambient aerosol (a) 2 h before and (b) 2 h after cloud events together with (c) the median size distribution of the cloud residuals (rightmost y-axis, marked in blue) measured behind the CVI. The overall median ambient aerosol particle size distribution is presented as the dotted line in all three panels. Numbers in parentheses mark the number of DMPS scans included in each median and the black dash-dotted lines mark the diameters analysed in the VHTDMA.
Fig. 4.
Measured VFR distributions as a function of time and D init. (a–c) together with the (d) BC mass fraction from the MAAP. The black lines represent the median VFR and the white circles mark cloud events (CVI in operation, VFR of cloud residuals). BC fraction of the cloud residuals during the longer cloud event are marked with a blue rectangle in panel d.
Table 2.
Mean and median measured VFR, together with the standard deviation and quartiles, of the ambient aerosols and cloud residuals, with total sampling times of 194 and 33 h, together with the estimated organic c* (µg m−3) and the predicted VFR of the PM, based on 7 filter samples.
Fig. 5.
Predicted VFR as a function of time and D init. Dashed lines represent the measured VFR as a function of time and D init. The black line illustrates the EM mass fraction in the PM10 and the dashed black line the BC mass fraction behind the CVI.
Fig. 6.
Measured hygroscopic GF as a function of time and D init. (a‒c). The black line represents the median GF and the white circles mark the cloud events (CVI in operation, GF of cloud residuals).
Table 3.
Mean and median measured GF and corresponding hygroscopicity parameter, κ, (together with the standard deviation and quartiles) for ambient aerosols and cloud residuals, with total sampling times of 235 and 87 h, respectively, presented together with the predicted κ values of the aerosol particles and cloud water, based on 19 filter samples and 7 water samples.
Fig. 7.
Hygroscopicity parameter, κ, determined from measured GF as a function time and D init. (red, blue and green dashed lines for D 100, D 200 and D 300, respectively) together with the κ values predicted with Equation (4) based on the chemical composition of the PM10 and cloud water samples (orange and grey solid lines, respectively).
Fig. 8.
(a) Predicted versus measured VFR, separated by D init. and coloured according to time of observation (see legend), were the error bars present the variability in the measurements and uncertainty of the predicted c*. (b) Predicted versus measurement-based κ value, separated in ambient aerosols and cloud residuals, where the error bars represent the variability of κ org. = 0.01–0.3. Dashed lines display the 1:1 line.