Quantitative Assessment of the Sulfuric Acid Contribution to New Particle Growth

Abstract

The Nano Aerosol Mass Spectrometer (NAMS) was deployed to rural/coastal and urban sites to measure the composition of 20-25 nm diameter nanoparticles during new particle formation (NPF). NAMS provides a quantitative measure of the elemental composition of individual, size-selected nanoparticles. In both environments, particles analyzed during NPF were found to be enhanced in elements associated with inorganic species (nitrogen, sulfur) relative to that associated with organic species (carbon). A molecular apportionment algorithm was applied to the elemental data in order to place the elemental composition into a molecular context. These measurements show that sulfate constitutes a substantial fraction of total particle mass in both environments. The contribution of sulfuric acid to new particle growth was quantitatively determined and the gas-phase sulfuric acid concentration required to incorporate the measured sulfate fraction was calculated. The calculated values were compared to those calculated by a sulfuric acid proxy that considers solar radiation and SO(2) levels. The two values agree within experimental uncertainty. Sulfate accounts for 29-46% of the total mass growth of particles. Other species contributing to growth include ammonium, nitrate, and organics. For each location, the relative amounts of these species do not change significantly with growth rate. However, for the coastal location, sulfate contribution increases with increasing temperature whereas nitrate contribution decreases with increasing temperature.

Identification and quantification of particle growth channels during new particle formation

“…During NPF, the sulfur and nitrogen mole fractions are larger and the carbon mole fraction is smaller than immediately before or after each event. A similar dependence of elemental mole fraction was noted previously for NPF in other locations (Bzdek et al, 2011(Bzdek et al, , 2012b. Note, however, that whereas the relative concentrations of S and C are anti-correlated, the absolute amounts of particulate S and C both increase substantially during NPF because there is a substantial increase in nanoparticle mass.…”

“…It is reasonable to assume all of the sulfur in these particles exists in the form of sulfate (Bzdek et al, 2012b). First, off-line and on-line molecular composition analyses of collected ultrafine particles in this location show sulfate as a major constituent in nanoparticles, with little to no contribution from other sulfur-containing species (Smith et al, 2010).…”

“…In this study, NAMS Zordan et al, 2008Zordan et al, , 2010Bzdek et al, 2011Bzdek et al, , 2012bBzdek et al, , 2013b) is used to obtain single particle mass spectra during NPF in Hyytiälä, Finland, from 21 March through 24 April 2011. NAMS provides a quantitative measure of nanoparticle elemental composition and in this study was set to analyze particles between 15 and 22 nm in diameter.…”

“…where GR MEAS is the measured growth rate, ν 1 the volume occupied by a hydrated H 2 SO 4 molecule,c 1 the mean thermal speed of the condensing monomer (Kuang et al, 2010), ρ particle the density of ambient particles during the time period of interest (estimated to be 1.3 g cm −3 ) (Kuwata et al, 2011), ρ sulfate the density of condensed phase sulfuric acid (1.8 g cm −3 ), and m = 1 MF sulfate , where MF sulfate is the average sulfate mass fraction for the time period of interest (Bzdek et al, 2012b). Equation (2) does not include the Fuchs-Sutugin correction for mass flux.…”

Shrinkage of Newly Formed Particles in an Urban Environment

“…Bzdek et al (2012) reports that NO 3 -, NH 4 + and organics contribute to 54-59% of new particle growth, whereas sulphates are responsible for the remaining 41-46% of the observed growth. Smith et al (2008) showed that the major compound of the newly formed particles are organics (~84%) and include organic acids (formate, acetate), hydroxyl organic acids and nitrogen-containing organic compounds.…”