2 research outputs found
A General Scavenging Rate Constant for Reaction of Hydroxyl Radical with Organic Carbon in Atmospheric Waters
Hydroxyl radical (OH) is an important
oxidant in atmospheric aqueous
phases such as cloud and fog drops and water-containing aerosol particles.
We find that numerical models nearly always overestimate aqueous hydroxyl
radical concentrations because they overpredict its rate of formation
and, more significantly, underpredict its sinks. To address this latter
point, we examined OH sinks in atmospheric drops and aqueous particles
using both new samples and an analysis of published data. Although
the molecular composition of organic carbon, the dominant sink of
OH, is extremely complex and poorly constrained, this sink behaves
very similarly in different atmospheric waters and even in surface
waters. Thus, the sink for aqueous OH can be estimated as the concentration
of dissolved organic carbon multiplied by a general scavenging rate
constant [<i>k</i><sub>C,OH</sub> = (3.8 ± 1.9) ×
10<sup>8</sup> L (mol C)<sup>−1</sup> s<sup>–1</sup>], a simple process that should significantly improve estimates of
OH concentrations in atmospheric drops and aqueous particles
Transboundary Secondary Organic Aerosol in Western Japan Indicated by the δ<sup>13</sup>C of Water-Soluble Organic Carbon and the <i>m</i>/<i>z</i> 44 Signal in Organic Aerosol Mass Spectra
The stable carbon
isotope ratio (δ<sup>13</sup>C) of low-volatile
water-soluble organic carbon (LV-WSOC) was measured in filter samples
of total suspended particulate matter, collected every 24 h in the
winter of 2010 at an urban site and two rural sites in western Japan.
Concentrations of the major chemical species in fine aerosol (<1.0
μm) were also measured in real time by aerosol mass spectrometers.
The oxidation state of organic aerosol was evaluated using <i>f</i><sub>44</sub>; i.e., the proportion of the signal at <i>m</i>/<i>z</i> 44 (CO<sub>2</sub><sup>+</sup> ions
from the carboxyl group) to the sum of all <i>m</i>/<i>z</i> signals in the organic mass spectra. A strong correlation
between LV-WSOC and <i>m</i>/<i>z</i> 44 concentrations
was observed, which suggested that LV-WSOC was likely to be associated
with carboxylic acids in fine aerosol. Plots of δ<sup>13</sup>C of LV-WSOC versus <i>f</i><sub>44</sub> showed random
variation at the urban site and systematic trends at the rural sites.
The systematic trends qualitatively agreed with a simple binary mixture
model of secondary organic aerosol with background LV-WSOC with an <i>f</i><sub>44</sub> of ∼0.08 and δ<sup>13</sup>C
of −17‰ or higher. Comparison with reference values
suggested that the source of background LV-WSOC was likely to be primary
emissions associated with C<sub>4</sub> plants