Relative humidity impact on aerosol parameters in a Paris suburban area

Abstract

Abstract. Measurements of relative humidity (RH) and aerosol parameters (scattering cross section, size distributions and chemical composition), performed in ambient atmospheric conditions, have been used to study the influence of relative humidity on aerosol properties. The data were acquired in a suburban area south of Paris, between 18 and 24 July 2000, in the framework of the "Etude et Simulation de la Qualité de l'air en Ile-de-France" (ESQUIF) program. According to the origin of the air masses arriving over the Paris area, the aerosol hygroscopicity is more or less pronounced. The aerosol chemical composition data were used as input of a thermodynamic model to simulate the variation of the aerosol water mass content with ambient RH and to determine the main inorganic salt compounds. The coupling of observations and modelling reveals the presence of deliquescence processes with hysteresis phenomenon in the hygroscopic growth cycle. Based on the Hänel model, parameterisations of the scattering cross section, the modal radius of the accumulation mode of the size distribution and the aerosol water mass content, as a function of increasing RH, have been assessed. For the first time, a crosscheck of these parameterisations has been performed and shows that the hygroscopic behaviour of the accumulation mode can be coherently characterized by combined optical, size distribution and chemical measurements.

Aerosol hygroscopicity parameter derived from the light scattering enhancement factor measurements in the North China Plain

“…To better describe the variation of f (RH), a stepwise function is applied to fit the f (RH) measurements. On the basis of previously suggested empirical functions (Carrico et al, 1998(Carrico et al, , 2000(Carrico et al, , 2003Kotchenruther et al, 1999;Hegg et al, 2002;Randriamiarisoa et al, 2006;), a specific polynomial segment fitting, with the critical RH of 60 %, is applied in the parameterization of f (RH), as (the parameterization results are displayed in Table 2)…”

“…It is usually defined as the ratio of aerosol light scattering coefficients at a given RH (σ sc (RH)) and at dry condition (σ sc,dry ), namely f (RH) = σ sc (RH)/σ sc,dry . Numerous studies have demonstrated that the parameterized f (RH) can be generally expressed as an exponential function of RH (Covert et al, 1972;Fitzgerald et al, 1982;Carrico et al, 1998Carrico et al, , 2000Carrico et al, , 2003Kotchenruther et al, 1999;Hegg et al, 2002;Randriamiarisoa et al, 2006;Cheng et al, 2008;Fierz-Schmidhauser et al, 2010a, b, c;Zieger et al, 2010Zieger et al, , 2013. It should be noted that, different from the size-resolved aerosol diameter growth factor (g(RH)), f (RH) represents the overall aerosol light scattering enhancement factor of the aerosol population, and is jointly determined by the particle number size distribution (PNSD), chemical composition, density and refractive index.…”

“…With increasing RH and mass fraction of condensed soluble materials onto fresh soot, the light scattering and absorption of soot particle could be evidently enhanced Pagels et al, 2009). Pilat and Charlson (1966) attempted to measure the aerosol light scattering enhancement factor with a tandem integrating nephelometer. In the following studies, Covert et al (1972) introduced a measuring method to determine the f (RH) at a set RH value with a humidified integrating nephelometer.…”

A parameterization of low visibilities for hazy days in the North China Plain

“…Both factors can be easily aquired, which makes the parameterization more practical. According to the relationship between K ex and aerosol volume concentration and the empirically exponential correlation between K ex and RH (Kasten, 1969;Carrico et al, 1998Carrico et al, , 2000Kotchenruther et al, 1999;Hegg et al, 2002;Randriamiarisoa et al, 2006;Eichler et al, 2008), the multiple regression scheme can be set up as follows:…”

Comparison of IASI water vapor retrieval with H<sub>2</sub>O-Raman lidar in the framework of the Mediterranean HyMeX and ChArMEx programs

“…Their assimilation in models leads to an improvement in weather forecasts (e.g., Collard and McNally, 2009;Bormann et al, 2010). Among the main components of the atmospheric state, water vapor is an essential element, which plays a key role in frontogenesis, convection (e.g., Held and Soden, 2000), cloud formation, and aerosol hydration (e.g., Larson and Taylor, 1983;Rood et al, 1987;Randriamiarisoa et al, 2006). In this way, it significantly influences the Earth climate and the atmospheric chemistry (e.g., IPCC, 2013).…”