3 research outputs found
Quantification of Byproduct Formation from Portable Air Cleaners Using a Proposed Standard Test Method
In response to the COVID-19 pandemic, air cleaning technologies
were promoted as useful tools for disinfecting public spaces and combating
airborne pathogen transmission. However, no standard method exists
to assess the potentially harmful byproduct formation from air cleaners.
Through a consensus standard development process, a draft standard
test method to assess portable air cleaner performance was developed,
and a suite of air cleaners employing seven different technologies
was tested. The test method quantifies not only the removal efficiency
of a challenge chemical suite and ultrafine particulate matter but
also byproduct formation. Clean air delivery rates (CADRs) are used
to quantify the chemical and particle removal efficiencies, and an
emission rate framework is used to quantify the formation of formaldehyde,
ozone, and other volatile organic compounds. We find that the tested
photocatalytic oxidation and germicidal ultraviolet light (GUV) technologies
produced the highest levels of aldehyde byproducts having emission
rates of 202 and 243 μg h–1, respectively.
Additionally, GUV using two different wavelengths, 222 and 254 nm,
both produced ultrafine particulate matter
Linking Load, Fuel, and Emission Controls to Photochemical Production of Secondary Organic Aerosol from a Diesel Engine
Diesel engines are important sources
of fine particle pollution
in urban environments, but their contribution to the atmospheric formation
of secondary organic aerosol (SOA) is not well constrained. We investigated
direct emissions of primary organic aerosol (POA) and photochemical
production of SOA from a diesel engine using an oxidation flow reactor
(OFR). In less than a day of simulated atmospheric aging, SOA production
exceeded POA emissions by an order of magnitude or more. Efficient
combustion at higher engine loads coupled to the removal of SOA precursors
and particle emissions by aftertreatment systems reduced POA emission
factors by an order of magnitude and SOA production factors by factors
of 2–10. The only exception was that the retrofitted aftertreatment
did not reduce SOA production at idle loads where exhaust temperatures
were low enough to limit removal of SOA precursors in the oxidation
catalyst. Use of biodiesel resulted in nearly identical POA and SOA
compared to diesel. The effective SOA yield of diesel exhaust was
similar to that of unburned diesel fuel. While OFRs can help study
the multiday evolution, at low particle concentrations OFRs may not
allow for complete gas/particle partitioning and bias the potential
of precursors to form SOA
Primary and Secondary Sources of Gas-Phase Organic Acids from Diesel Exhaust
Organic
acids have primary and secondary sources in the atmosphere,
impact ecosystem health, and are useful metrics for identifying gaps
in organic oxidation chemistry through model-measurement comparisons.
We photooxidized (OH oxidation) primary emissions from diesel and
biodiesel fuel types under two engine loads in an oxidative flow reactor.
formic, butyric, and propanoic acids, but not methacrylic acid, have
primary and secondary sources. Emission factors for these gas-phase
acids varied from 0.3–8.4 mg kg<sup>–1</sup> fuel. Secondary
chemistry enhanced these emissions by 1.1 (load) to 4.4 (idle) ×
after two OH-equivalent days. The relative enhancement in secondary
organic acids in idle versus loaded conditions was due to increased
precursor emissions, not faster reaction rates. Increased hydrocarbon
emissions in idle conditions due to less complete combustion (associated
with less oxidized gas-phase molecules) correlated to higher primary
organic acid emissions. The lack of correlation between organic aerosol
and organic acid concentrations downstream of the flow reactor indicates
that the secondary products formed on different oxidation time scales
and that despite being photochemical products, organic acids are poor
tracers for secondary organic aerosol formation from diesel exhaust.
Ignoring secondary chemistry from diesel exhaust would lead to underestimates
of both organic aerosol and gas-phase organic acids