Abstract

ANDRACA-AYALA, G.  and  RUIZ-SUAREZ, L. G.. Partitioning of formaldehyde between gas phase and particles (PM_2.5) in México City. Atmósfera [online]. 2005, vol.18, n.3, pp.189-203. ISSN 0187-6236.

An annular denuder/filter-pack sampling technique has been employed to get an insight of the formaldehyde partitioning between gas phase and particles (PM_2.5) in México City using short time sampling periods. Formaldehyde was trapped using DNPH derivatives and analyzed by HPLC/UV. One annular denuder was used to trap formaldehyde from the gas phase followed by a Teflon filter to trap PM_2.5, and a second backup denuder was used to trap degassed formaldehyde from the filter. Just after finishing the sampling, filters were soaked in a DNPH solution to fix the PM_2.5 formaldehyde, and the denuders where extracted with another DNPH solution. The sum of the concentrations in both phases ranged from 7.90 to 44.60 µ/m³ during the sampling periods from 8 a.m. to noon in several ocassions from 2000 to 2003. In average, the formaldehyde PM_2.5/gas-phase ratio was about 0.15, one hundred times higher than previously observed. A large fraction of the formaldehyde in particles is easily lost by a combination of three processes: two of these, blow off from the trapped particles and displacement of the phase equilibrium, both well known and confirmed in other studies. A third process called extrussion of particles is described. Thus, PM_2.5 may act as a temporal sink or a slow releasing source of formaldehyde in México City's photochemical smog. This findings may have strong implications for air quality modeling.

Keywords : Denuder; formaldehyde; México City; PM2.5 sampling.

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