Methods For Sampling And Analysis Of Tropospheric Ethanol In Gaseous And Aqueous Phases

Chemosphere 52 (2003) 1307–1319 www.elsevier.com/locate/chemosphere

Methods for sampling and analysis of tropospheric ethanol in gaseous and aqueous phases
A. Monod
a

a,*

, N. Bonnefoy b, P. Kaluzny

b,c

, I. Denis c, P. Foster c, P. Carlier

d

Laboratoire de Chimie et Environnement, Universit de Provence, case 29, 3 Place V. Hugo, 13331 Marseille Cedex 3, France e b TERAEnvironnement, MBE 157, 3 Place Sainte Claire, 38000 Grenoble, France c Groupe de Recherche sur l’Environnement et la Chimie Atmosphrique, Universit Joseph Fourier, e e 39 boulevard Gambetta, 38000 Grenoble, France d Laboratoire Interuniversitaire des Systmes Atmosphriques, Tour 44-45, 2 Place Jussieu, 75251 Paris Cedex 05, France e e Received 22 July 2002; received in revised form 26 February2003; accepted 13 March 2003

Importance of this paper: Oxygenated VOCsÕ impact on the oxidizing capacity of the troposphere is not known because of a lack of data on their atmospheric concentrations and behaviour (reactivity, scavenging. . .). The demand for analytical methods to detect these compounds in both the gas and aqueous phases has therefore grown in the last two decades. This paperfocuses on the development of experimental techniques for measuring ethanol, which is widely used as a vehicle fuel additive and as an industrial solvent. In order to compare different techniques for gas phase detection, field measurements of ethanol were made at urban locations. These measurements also complete the available data in the literature, especially for the liquid phase. Abstract In thispaper, we report on techniques for sampling and measuring ethanol in both the gas and aqueous phases of the lower troposphere. In the gas phase, the best sampling conditions were ensured by adsorption on Hayesep Q with a Chromosorb W AW coated with LiCl dryer (method 1) or by cryogenic trapping (method 2). An intercomparison campaign showed good agreement between both methods under variousconditions. Method 1 (adsorption on Hayesep Q with dryer) is easier to set up and to carry away from the laboratory. Method 2 (cryogenic trapping) requires longer sampling time (up to 60 min while method 1 requires only 10–15 min). Method 1 is adapted to high concentrations of ethanol (>20 ppb) and low relative humidity (30 44 36 45 48 48 39 38 40 46 49

10.1 – – – – – – – – – –

The signed differenceswere calculated between method 2 and method 1.

adsorption on solid adsorbents (Table 4). These techniques are compared and discussed in details in the following. Gholson et al. (1990) show that small polar compounds such as ethanol are lost in aluminium canisters, and they recommend to use stainless steel canisters. However, sampling alcohols with these canisters requires specific conditions(McClenny et al., 1991). Most studies recommend to store polar compounds in stainless steel canisters in humidified air, because water molecules adsorbed on the inside walls passivate the active sites, allowing the polar compounds to remain in the gas phase (Gholson et al., 1990; Pate et al., 1992). Nevertheless, storage time of polar compounds under these conditions seems to be limited to one day(Gholson et al., 1990; Pate et al., 1992; Kirstine et al., 1998). After one day, some authors found slow losses of alcohols (Gholson et al., 1990; Kelly et al., 1993), while other authors found slow productions of alcohols (Pate et al., 1992; Brymer et al., 1996). The performances obtained with this method are reported in Table 4 (Panel a). This technique was mostly used to observe high concentrationsof ethanol in the atmosphere. In general, the corresponding detection limits for ethanol are quite high compared to other techniques. A few authors tested several solid adsorbents to sample alcohols. They found that classical adsorbents such as Tenax TA and carbotrap (Rothweiler et al., 1991), anasorb 747, porasil C/n-octane, carbopack B, carbotrap C and Tenax GR (Sunesson et al., 1995) show...