Seasonal and diurnal characteristics of water soluble inorganic compounds in the gas and aerosol phase in the Zurich area

Abstract

Abstract. Gas and aerosol samples were taken using a wet effluent diffusion denuder/aerosol collector (WEDD/AC) coupled to ion chromatography (IC) in the city of Zurich, Switzerland from August to September 2002 and in March 2003. The water soluble inorganic anions nitrate, sulfate, and nitrite were analyzed online with a time resolution of two hours for the gas and aerosol phase. The fraction of water soluble inorganic anions in PM10 varied from 15% in August to about 38% in March. Seasonal and diurnal variations of nitrate in the gas and aerosol phase were observed with more than 50% of the total nitrate in the gas phase during August and more than 80% of nitrate in the aerosol phase during March, in the latter case exceeding the concentration of sulfate by a factor of 2. Aerosol sulfate, on the other hand, did not show significant variability with season. However, in the gas phase, the SO 2 concentration was 6.5 times higher in winter than in summer. Nitrous acid (HONO) also showed a diurnal variation in both the gas and aerosol phase with the lowest concentration (0.2-0.6 µg/m 3 ) in the afternoon. The mixing ratios of the primary pollutants, NO, CO and SO 2

Semi-continuous gas and inorganic aerosol measurements at a Finnish urban site: comparisons with filters, nitrogen in aerosol and gas phases, and aerosol acidity

“…These diurnal cycles resemble those observed at other sites, for instance Zürich (Fisseha et al, 2006), Pittsburgh (Wittig et al, 2004), and Oensingen, Switzerland (Wolff et al, 2010): the peak nitrate concentration is a few hours earlier than that of HNO 3 . The time lag can be explained by the temperature dependent partitioning of ammonium nitrate between the gas and aerosol phase (e.g., Fisseha et al, 2006). The times of the diurnal maxima are not quite the same at the sites.…”

“…For example, in Oensingen in the late summer of 2006, the maximum HNO 3 concentration was clearly later in the afternoon (16:00-17:00) (Wolff et al, 2010), which is about 4 h later than in our spring period in Helsinki. In our study the HNO 3 concentration decreased in the afternoon, probably due to dry deposition and heterogeneous formation of nitrate, as suggested for example by Fisseha et al (2006) for the similar cycle in Zürich. The day-to day variation of HNO 3 was large in our data, which is due to variation in both sources and removal.…”

“…9). This again resembles the cycle in Zürich, Switzerland, where HONO reached maximum at about 09:00 and decreased during the day until it reached minimum at 17:00 in March 2003 (Fisseha et al, 2006).…”

“…Another semicontinuous method that uses a SJAC is the ambient ion monitor (AIM, URG Corporation, USA) that determines the concentrations of several anions and cations in aerosol (e.g., Wu and Wang, 2007;Nie et al, 2010) and exists in four different configurations (URG 9000A-D) that have different performances. Yet another method that is based on the same principle is the Dionex Gas Particle Ion Chromatography (GPIC) system that measures concentrations of water-soluble inorganic aerosol constituents (Cl − , NO ) and their associated precursor gases (HCl, SO 2 , HNO 3 , NH 3 ) (Godri et al, 2009). The ability to measure both water-soluble aerosol and the precursor gas concentrations at a high time resolution has recently been shown to be especially valuable for evaluating models, for instance the secondary inorganic aerosol formation (Schaap et al, 2011) and the gas-aerosol partitioning of ammonium nitrate (Aan de Brugh et al, 2012).…”

Illustrating the benefit of using hourly monitoring data on secondary inorganic aerosol and its precursors for model evaluation

“…We have found that the thermodynamic equilibrium module produces a too stable ammonium nitrate in winter and during night time in summer, whereas during the daytime in summer it is too unstable. Earlier studies have also identified an underestimation of the particulate nitrate concentrations during summer and daytime (Moya et al, 2001;Fisseha et al, 2006;Morino et al, 2006). In contrast, a number of studies have shown that the predicted equilibrium is generally in accordance with observations (Zhang et al, 2003;Takahama et al, 2004;Yu et al, 2005), though also in these studies significant discrepancies between measured and predicted partitioning have been observed.…”