Quantitative Time-Resolved Monitoring of Nitrate Formation in Sea Salt Particles Using a CCSEM/EDX Single Particle Analysis

Abstract

Progress of the nitrate formation in individual sea salt particles was detected as a function of time using aerosol samples collected during the TexAQS 2080 experiment We demonstrate that the time-resolved collection approach coupled with the automated EDX single particle analysis made it possible to follow in detail the time evolution of sea salt particles within a diverse aerosol mixture. Using a custom built Time-Resolved Aerosol Collector (TRAC), particulate samples were taken sequentially on grid-supported 50 nm carbon films with a time resolution of 10 min between two consecutive samples. The samples were analyzed in the laboratory using Computer Controlled Scanning Electron Microscopy with Energy-Dispersed analysis of X-rays (CCSEM/EDX). Between midnight of 08/16/00 and the early morning of 08/17/00, a steady, particularly sea salt rich aerosol was observed at the measurement site, which later showed the effects of atmospheric processing. During the night of 08/17/00 the sea salt particles were almost unprocessed, having elemental composition close to that of seawater. By 12 noon, the evolving atmosphere was able to completely convert them, predominantly to sodium nitrate particles. During the next night this process had nearly stopped and fairly virgin sea salt particles appeared again.

Raman Microspectroscopic Analysis of Size-Resolved Atmospheric Aerosol Particle Samples Collected with an ELPI: Soot, Humic-Like Substances, and Inorganic Compounds

“…The high proportion of sodium nitrate can be attributed to the uptake of nitric acid and replacement of chloride by nitrate in aged sea salt particles (Gard et al 1998;Laskin et al 2002;Krüger et al 2003). No nitrates were found on stages 7 and 8, which is consistent with the results of Batonneau et al (2006).…”

Enhanced surface photochemistry in chloride–nitrate ion mixtures

“…These particle measurements were carried out to ensure that equal aerosol particle sizes and concentrations were present as the ratio of chloride to nitrate changed. While these sizes are typical of both processed and unprocessed sea salt particles in air, 8 some coalescence of particles on the Teflon s surface occurred to give larger particles. The aerosol layer contained 2-4 mmol of salt, calculated from measurements of mass and published water activity data.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The particle composition has been observed to range from no Cl À depletion (fresh sea salt) to complete Cl À depletion (heavily processed sea salt), and a strong anticorrelation of Cl À with NO 3 À has been reported. 4,7,8 As a result, the ratio of Cl À to NO 3 À in sea salt-derived aerosol decreases as air masses move downwind in coastal urban regions. While nitrate ions are often treated as a stable end product of this chemistry, NO 3 À absorbs light in the actinic region above 290 nm and photodissociates via two reaction channels: 16 NO…”

Diverse Chemical Mixing States of Aerosol Particles in the Southeastern United States

“…Particles on MOUDI stages 4-11 (Da = 0.056-1.8 µm, Figure 1) were analyzed using CCSEM (FEI Quanta environmental SEM) equipped with a field emission gun operating at 20 kV and a high angle annular dark field (HAADF) detector (Laskin et al, 2006;Laskin et al, 2002;Laskin et al, 2012). The SEM was equipped with an EDX spectrometer (EDAX, Inc.) which was used to quantify X-rays of elements with 20 atomic numbers > C (Z = 6).…”