Measurement of Atmospheric Nitric Acid in Gas Phase and Nitrate in Particulate Matter by means of Annular Denuders

Particulate Nitrate Measurement Using Nylon Filters

“…[5][6][7][8] Dissociation of NH 4 NO 3 increases with increasing temperature and decreases with increasing relative humidity (RH) above the deliquescence point. 9 NO 3 Ϫ can also be found in aerosol particles in other forms, including sodium nitrate (NaNO 3 ) and calcium nitrate [Ca(NO 3 ) 2 ], reflecting, for example, reactions of HNO 3 or its precursors with sea salt or suspended soil particles. 10 Most routine aerosol monitoring networks, however, assume that NO 3 Ϫ measured is in the form of NH 4 NO 3 .…”

“…[11][12][13][14][15][16][17][18][19][20][21] Positive NO 3 Ϫ measurement artifacts, for example, can be caused by collection of gaseous HNO 3 and/or other nitrogen oxides with subsequent reaction on filter media. The use of diffusion denuders upstream of particle sampling filters can effectively remove HNO 3 (and perhaps other species depending on denuder coating), thereby minimizing this artifact. 3,[22][23][24] If the denuder can be extracted and the extract analyzed, this approach offers the additional advantage of being able to quantify gas phase HNO 3 concentrations, aiding understanding of the gas-particle equilibrium described above.…”

“…[1][2][3] Ammonium nitrate (NH 4 NO 3 ), generally the predominant form of NO 3 Ϫ in submicron aerosol particles, is formed by reaction of gaseous nitric acid (HNO 3 ) and ammonia (NH 3 ) as shown in eq 1. 4 NH 3 (g) ϩ HNO 3 (g) 7 NH 4 NO 3 (p)…”

Improved Time-Resolved Measurements of Inorganic Ions in Particulate Matter by PILS-IC Integrated with a Sample Pre-Concentration System

“…The first denuder, for the removal of acid gases, was coated with 1% Na 2 CO 3 C 2% glycerine in ethanol-water solution (50:50); the second one, for the removal of ammonia, was coated with 1% H 3 PO 4 in the same solution. At the operative flow rate, the removal efficiency of these annular denuder is better than 95% (Allegrini et al 1987;Perrino et al 1990;Allegrini et al 1994). Loading capacity of each denuder is above 1 mg, so they could be substituted every three days (Perrino and Gherardi 1999).…”

“…These sampling artifacts can be efficiently reduced by using diffusion lines, that is, a number of diffusion denuders and a filter pack set in series, but the use of this technique increases laboratory work and analytical costs even more (Allegrini et al 1994;Perrino, Ramirez et al 2001).…”