In-situ chemical and hygroscopic properties of submicron aerosol particles using mass spectrometry at Puy-de-Dôme, France.

E.J.Freney, Good N, Monier M, Weigel R, Laj P, Pichon J.M, and Sellegri K LaMP, CNRS-Université Blaise Pascal, 63117Aubiére Cedex, France

An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at Puy-De-Dome station (1465 m above sea level, 45°46 N 2°51E) during autumn 2008, spring 2009, and summer 2010 as part of the European Monitoring and Evaluation Program (EMEP). Chemical composition and size of aerosol particles were acquired in an effort to characterise the aerosol in the continental free troposphere. Simultaneous aerosol particle measurements included particle size information using two scanning mobility particle sizer (SMPS), one located behind a whole air inlet (WAI) and the other behind a interstitial inlet and a hygroscopicity tandem differential mobility analyser (HTDMA). The hygroscopic properties of aerosol particles are fundamental to their effectiveness as cloud condensation nuclei. Hygroscopic measurements using HTDMA reveal different hygroscopic modes of the aerosol population, providing information on the mixing state of the aerosol particles.

In this work, we compare calculated values of particle hygroscopicities (к) from a HTDMA and an AMS. The best agreement between the two measurements is only obtained when the mixing state of the aerosol population is considered. In addition, we used a combination of SPMS and HTDMA growth factor measurements to show that hygroscopicity can have a considerable impact on particle activation curves. This is contrary to recent findings which show that particle activation curves can be predicted using only particle size (e.g. Duseck et al., 2006) but in agreement with others suggesting that particle composition and hygroscopicity results in large differences in the cloud condensation nuclei (CCN) properties (e.g. Antila et al 2009).

Acknowledgements : This work has been partially funded by European Commission 6th Framework program project EUCAARI and EUSAAR. Evelyn Freney has been supported by CNRS fellowship.

Laboratoire de Météorologie Physique, http://wwwobs.univ-bpclermont.fr/atmos

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IntroductionPredicting the growth factor using the AMS

A mixing rule was used to convert the inorganic ions measured by the AMS into solutes (Zavari 2005). The growth factors (GF) of the individual solutes(i)(Toppings, 2005) and the organic (assumed to be 1.1, p=1400 kg m-3 were then combined using the Zdanovskii-Stokes-Robinson ( ZSR) rule to predict the GF of aerosol particles at 90% RH using:

Once GF(RH) is predicted a corresponding K value can be calculated using

Topping, D. O., McFiggans, G. B., and Coe, H.: A curved multicomponent aerosol hygroscopicity model framework: Part 1 – Inorganic compounds, Atmos. Chem. Phys., 5, 1205–1222, 2005a,

Zaveri, R. A., Easter, R. C., and Wexler, A. S.: A new method for multicomponent activity coefficients of electrolytes in aqueous atmospheric aerosols, J. Geophys. Res.-Atmos., 110, D02201, doi:10.1029/2004JD004681, 2005.

Petters, M. D. and Kreidenweis, S. M.: A single parameter representation of hygroscopic growth and cloud condensation nucleus activity, Atmos. Chem. Phys., 7, 1961–1971, 2000

Summary and Conclusions

The AMS was deployed on top of Puy-de-Dome during autumn 2008, spring 2009, and summer 2010. The dominant back trajectories were arriving from the continent with the exception of a few days when local air masses dominated. Using the AMS, size-resolved chemical composition of non-refractory submicron particles (NR-PM1) were obtained at 1-min resolution. The average composition of NR-PM1 during this study (during cloud free periods) was 34% organics, 30% sulfate, 20% nitrate, 17% ammonium, and 0.4% chloride. The fraction or organic-bearing particles detected by the AMS increased during periods influenced by local air masses. The average size distributions of sulfate, nitrate, and ammonium were very similar and characterized by a prominent accumulation mode peaking at Dva ≈ 550 nm.

We derived particle hygroscopicities (к) of atmospheric aerosol particles from both HTDMA measurements and AMS measurements. The majority of the variation between the кAMS and кHTDMA can be explained for by not accounting for externally mixing when predicting кAMS. The aerosol population was externally mixed with hydrophobic (GF <1.3) mode varying between 20% and 60% during sampling. Best agreements between кAMS and кHTDMA were observed when the aerosol population was dominated (>80%) by the hydroscopic (GF >1.35) mode.

The effect of particle hygroscopicity on their activation curves was determined using a combination of dual-SMPS and HTDMA data. We observe that for particles with diameters between 50 nm and 200 nm, hygroscopicity plays an important role in the shape of the activation curve. This is contrary to recent findings which show that particle activation curves can be predicted using only particle size (e.g. Duseck et al., 2006) but in agreement with others suggesting that particles composition and hygroscopicity results in large differences in the cloud condensation nuclei properties (e.g. Antila et al. 2009). Using AMS measurements during cloud events we find that the organic aerosol particles are dominant particle type in the interstitial phase. This verifies the chemical dependence of particle hygroscopicity on activation properties. Our results illustrate that accounting for particle chemistry and hygroscopicity as well as size will likely provide more accurate predictions on cloud condensation nucleating ability.

References

Antila, T., Vaattovaara, P., Komppula, M., Hyvarinen, A.-P., Lihavainen, H, Kerminen, V.-M, Laaksonen, : Size-dependant activation of aerosols into cloud droplets at a subartic background site duringthe second Pallas Cloud Experiment (2nd PACE): method development and data evaluation, Atmos. Chem. Phys., 9, 4841-484, 2009.

Dusek, U., Frank, G.P., Hildebrandt, L., Curtius, J., Schneider, J., Walter, S., Chand, D., Drewnick, F., Hings, S., Jung, D., Borrmann, S., and Andreae, M. O.: Size matters more than chemistry for cloud-nucleating abilities of aerosol particles, Science, 312, 1375-1378, 2006

Venzac, H. ; Sellegri, K. ; Villani, P. ; Picard, D. ; Laj, P. Seasonal variation of aerosol size distributions in the free troposphere and residual layer at the puy de Dôme station, France Atmos. Chem. Phys. Vol. 9 , No. 4 , p. 1465-1478, 2009

Aerosol mass spectrometry measurements at Puy de Dôme

Impact of hygroscopicity on particle activation curves

Comparison of calculated K values for HTDMA and AMSComparison of measured (grey lines) and predicted (coloured points) timeseries of the two hygroscopic modes (GF > 1.3 and GF < 1.3) observed at the puy de dôme.

Autumn 2008 Spring 2009 Summer 2010

Diurnal variations

Positive matrix factorisation analysis of the organic mass spectra

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