Characterization of a catalyst-based conversion technique to measure total particulate nitrogen and organic carbon and comparison to a particle mass measurement instrument
The chemical composition of aerosol particles is a key aspect in determining their impact on the environment. For example, nitrogen-containing particles impact atmospheric chemistry, air quality, and ecological N deposition. Instruments that measure total reactive nitrogen (N<sub>r</sub&...
Main Authors: | , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2018-05-01
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Series: | Atmospheric Measurement Techniques |
Online Access: | https://www.atmos-meas-tech.net/11/2749/2018/amt-11-2749-2018.pdf |
Summary: | The chemical composition of aerosol particles is a key aspect in determining their impact
on the environment. For example, nitrogen-containing particles impact
atmospheric chemistry, air quality, and ecological N deposition. Instruments
that measure total reactive nitrogen (N<sub>r</sub> = all nitrogen compounds
except for N<sub>2</sub> and N<sub>2</sub>O) focus on gas-phase nitrogen and
very few studies directly discuss the instrument capacity to measure the mass
of N<sub>r</sub>-containing particles. Here, we investigate the mass
quantification of particle-bound nitrogen using a custom N<sub>r</sub> system
that involves total conversion to nitric oxide (NO) across platinum and
molybdenum catalysts followed by NO−O<sub>3</sub> chemiluminescence detection.
We evaluate the particle conversion of the N<sub>r</sub> instrument by
comparing to mass-derived concentrations of size-selected and counted
ammonium sulfate ((NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>), ammonium nitrate
(NH<sub>4</sub>NO<sub>3</sub>), ammonium chloride (NH<sub>4</sub>Cl), sodium nitrate
(NaNO<sub>3</sub>), and ammonium oxalate ((NH<sub>4</sub>)<sub>2</sub>C<sub>2</sub>O<sub>4</sub>)
particles determined using instruments that measure particle number and size.
These measurements demonstrate N<sub>r</sub>-particle conversion across the
N<sub>r</sub> catalysts that is independent of particle size with
98 ± 10 % efficiency for 100–600 nm particle diameters. We also
show efficient conversion of particle-phase organic carbon species to
CO<sub>2</sub> across the instrument's platinum catalyst followed by a
nondispersive infrared (NDIR) CO<sub>2</sub> detector. However, the
application of this method to the atmosphere presents a challenge due to the
small signal above background at high ambient levels of common gas-phase
carbon compounds (e.g., CO<sub>2</sub>). We show the N<sub>r</sub> system is an
accurate particle mass measurement method and demonstrate its ability to
calibrate particle mass measurement instrumentation using single-component,
laboratory-generated, N<sub>r</sub>-containing particles below
2.5 µm in size. In addition we show agreement with mass
measurements of an independently calibrated online particle-into-liquid
sampler directly coupled to the electrospray ionization source of a
quadrupole mass spectrometer (PILS–ESI/MS) sampling in the negative-ion mode.
We obtain excellent correlations (<i>R</i><sup>2</sup> = 0.99) of particle mass
measured as N<sub>r</sub> with PILS–ESI/MS measurements converted to the
corresponding particle anion mass (e.g., nitrate, sulfate, and chloride). The
N<sub>r</sub> and PILS–ESI/MS are shown to agree to within ∼ 6 %
for particle mass loadings of up to 120 µg m<sup>−3</sup>. Consideration
of all the sources of error in the PILS–ESI/MS technique yields an overall
uncertainty of ±20 % for these single-component particle streams.
These results demonstrate the N<sub>r</sub> system is a reliable direct
particle mass measurement technique that differs from other particle
instrument calibration techniques that rely on knowledge of particle size,
shape, density, and refractive index. |
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ISSN: | 1867-1381 1867-8548 |