Abstract
Abstract. Aerosol hygroscopic growth factors and chemical properties were measured as part of the MEGAPOLI "Megacities Plume Case Study" at the urban site Laboratoire d'Hygiène de la Ville de Paris (LHVP) in the city center of Paris from June to August 2009, and from January to February 2010. Descriptive hygroscopic growth factors (DGF) were derived in the diameter range from 25 to 350 nm at relative humidities of 30, 55, 75, and 90% by applying the summation method on humidified and dry aerosol size distributions measured simultaneously with a humidified differential mobility particle sizer (HDMPS) and a twin differential mobility particle sizer (TDMPS). For 90% relative humidity, the DGF varied from 1.06 to 1.46 in summer, and from 1.06 to 1.66 in winter. Temporal variations in the observed mean DGF could be well explained with a simple growth model based on the aerosol chemical composition measured by aerosol mass spectrometry (AMS) and black carbon photometry (MAAP). In particular, good agreement was observed when sulfate was the predominant inorganic factor. A clear overestimation of the predicted growth factor was found when the nitrate mass concentration exceeded values of 10 μg m−3, e.g., during winter.
Highlights
Aerosol particles are ubiquitous in the atmosphere and play an important role in a variety of fields such as the terrestrial radiation budget, atmospheric chemistry, climate, and human health
One notable requirement for successful application of the SM is that the total number under the complete PNSD remains constant with humidification. This implies that no particles are lost or formed during the humidification process. If this is the case, the particle number concentrations measured by the twin differential mobility particle sizer (TDMPS) and the humidified differential mobility particle sizer (HDMPS) are the same, and the humidification may be considered as a size distribution rearrangement (Birmili et al, 2009)
4 Results 4.1 Campaign overview The measurements in the city center of Paris started in the MF organic matter a) 0.8
Summary
Aerosol particles are ubiquitous in the atmosphere and play an important role in a variety of fields such as the terrestrial radiation budget, atmospheric chemistry, climate, and human health. More in situ measurements with coupled measurements of particle composition and their hygroscopic behavior are needed Conducting more of those measurements, laboratory studies and hygroscopic growth models can be associated with field measurements. The vast number of different organic species in the atmosphere (e.g., Saxena and Hildemann, 1996) combined with a limited understanding of organic aerosol hygroscopicity has led to the practice of assigning the water uptake of organics as the particle growth not explained by inorganic constituents (e.g., Malm et al, 2005). This study compares measured and calculated hygroscopic growth factors from field measurements of the aerosol chemical composition and particle number size distributions in the city center of Paris, France. Our study is the first one investigating HDMPS size resolved particle growth (cf. HDMPS vs. HTDMA differences in Sect. 3.1) in combination with chemical measurements with high time resolution in a European megacity
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