Strong and weak acidity of aerosols collected over the northeastern United States

Abstract

Total sulfate, acidity, and principal cations were measured in aerosol samples collected from an aircraft over the northeastern United States and at ground level on filters protected by a denuder tube for NH3. Aerosol acidity was determined by aqueous extraction of the filters and titration with NaOH. Strong and weak acid components were resolved by using Gran plots, and for 30 fall and summer samples the weak acidity comprised x ± s = 26 ± 12% of the total acidity. The strong acidity averaged 25 ± 18% of the total sulfate equivalents. Hydrogen ion plus ammonium ion balanced closely the sulfate ion concentration with the ratio of equivalents of [(H+) + (NH4+)]/(S042_) = 1.03 ± 0.14 for 36 samples. A phase diagram for the H20-H2S04-(NH4)2S04 system was used to determine that the aerosol particles were liquid at the ambient relative humidity in 24 of 47 cases. For the 24 liquid samples the calculated pH averaged 0.11 ± 0.59.

Uptake kinetics of 3-buten-1-ol, 4-penten-1-ol and 3-methyl-3-buten-1-ol into sulfuric acid solutions

“…However, significantly higher sulfate aerosol acidity, approaching values used in this study has also been reported [22,23] and used in other experiments [24][25][26][27]. Thus, this heterogeneous reaction could potentially occur in the ambient atmosphere.…”

“…Experimental data from this study allows the individual estimation of atmospheric lifetimes for these three unsaturated alcohols, for their reaction with H 2 SO 4 . After consulting atmospheric conditions of H 2 SO 4 content [22,23], γ values were adopted from 60 wt%-80 wt% H 2 SO 4 data given in Table 1. The atmospheric lifetimes, τ, of the unsaturated alcohols with regard to their uptake into H 2 SO 4 solution could be estimated by: τ = 4/γωσ, where ω is the mean molecular speed of the alcohol, and σ is the area density of the atmospheric sulfate aerosol (~2×10 -7 cm 2 /cm 3 [28]).…”

Estimation of the rate constant for the reaction of acid sulphate aerosol with NH3 gas from atmospheric measurements

“…The existence of acidic sulphate aerosols in the atmosphere has been widely reported in the literature (Tanner et al, 1977;Elshout et al, 1978;Cobourn et nl., 1980;Ferek et al, 1983;Koutrakis et al, 1988;Pierson et al, 1988;Waldman et nl., 1990). Formation of sulphuric acid in the atmosphere is by the oxidation of SO, through either homogeneous or heterogeneous pathways.…”

Contribution of Water to Particulate Mass in the South Coast Air Basin

“…The difference of chemical composition is primarily responsible for the pH difference at different locations. For comparison, for northeastern US., Ferek et al (1983) estimated the particulate pH to range between -0.8 and 2.0 over 24 samples (April 1979-August 1980. The estimated low pH at San Nicolas Island (not shown) was due to the absence of basic compounds such as ammonium.…”