Importance of mineral cations and organics in gas-aerosol partitioning of reactive nitrogen compounds: case study based on MINOS results S. Metzger1, N. Mihalopoulos2, and J. Lelieveld1 1Max Planck Institute for Chemistry, Air Chemistry Department, Mainz, Germany 2University of Crete, Department of Chemistry, Heraklion, Greece
Abstract. The partitioning of reactive nitrogen compounds between
the gas and the aerosol phase, as observed during the MINOS (Mediterranean
INtensive Oxidant Study) campaign in Crete, Greece, in July and August 2001,
has been studied with three thermodynamic gas-aerosol equilibrium models
(EQMs) of different chemical complexity: ISORROPIA, which is limited to the
ammonium-sulfate-nitrate-sodium-chloride-water-system; SCAPE2, which also
includes mineral elements (calcium, magnesium and potassium); and EQSAM2,
which additionally accounts for organic acids. The different EQMs are
constrained by measured gas (g) and aerosol (a) concentrations: Total ammonia
(NH3(g) and NH4(a)+), total nitrate (HNO3(g) and
NO3(a)-), total sulfate (H2SO4(g) and
SO4(a)2-), total chloride (HCl(g) and Cl-(a)),
sodium (Na+(a)), calcium (Ca2+(a)), magnesium
(Mg2+(a)), potassium (K+(a)) and organic acids (a).
Although the three EQMs differ considerably in particular aspects, their
application at the same level of complexity yields comparable results for
the equilibrium composition and phase partitioning of ammonia and nitric
acid, i.e. within the range of measurement uncertainties (~10%).
Their application at different levels of complexity, however, gives rise to
substantial differences for the gas-aerosol partitioning of reactive
nitrogen compounds. Our results show that only if (soluble) mineral
components and (lumped) organic acids are accounted for, the observed
gas-aerosol partitioning of ammonia and nitric acid can be accurately
reproduced for air pollution episodes characterized by a complex chemical
mixture, typical for the Mediterranean lower atmosphere.
Citation: Metzger, S., Mihalopoulos, N., and Lelieveld, J.: Importance of mineral cations and organics in gas-aerosol partitioning of reactive nitrogen compounds: case study based on MINOS results, Atmos. Chem. Phys., 6, 2549-2567, doi:10.5194/acp-6-2549-2006, 2006.