Effects of phase structure of MnO2 and morphology of δ-MnO2 on toluene catalytic oxidation

. In the present work, we performed chassis dynamometer experiments to
investigate the emissions and secondary organic aerosol (SOA) formation
potential of intermediate-volatility organic compounds (IVOCs) from an
on-road Chinese gasoline vehicle. High IVOC emission factors (EFs) and
distinct volatility distribution were recognized. The IVOC EFs for the
China V vehicle ranged from 12.1 to 226.3  mg per kilogram fuel , with
a median value of 83.7  mg per kilogram fuel , which was higher than
that from US vehicles. Besides, a large discrepancy in volatility distribution
and chemical composition of IVOCs from Chinese gasoline vehicle exhaust was
discovered, with larger contributions of B14 – B16 compounds
(retention time bins corresponding to C 14 -C 16 n -alkanes) and a higher
percentage of n -alkanes. Further we investigated the possible reasons that
influence the IVOC EFs and volatility distribution and found that fuel
type, starting mode, operating cycles and acceleration rates did have an
impact on the IVOC EF. When using E10 (ethanol volume ratio of 10 %, v / v )
as fuel, the IVOC EF of the tested vehicle was lower than that using
commercial China standard V fuel. The average IVOC-to-THC (total hydrocarbon) ratios for
gasoline-fueled and E10-fueled gasoline vehicles were 0.07±0.01 and
 0.11±0.02 , respectively. Cold-start operation had higher IVOC EFs
than hot-start operation. The China Light-Duty Vehicle Test Cycle (CLTC) produced
70 % higher IVOCs than those from the Worldwide Harmonized Light Vehicles
Test Cycle (WLTC). We found that the tested vehicle emitted more IVOCs at
lower acceleration rates, which leads to high EFs under CLTC. The only
factor that may influence the volatility distribution and compound
composition is the engine aftertreatment system, which has compound and
volatility selectivity in exhaust purification. These distinct
characteristics in EFs and volatility may result in higher SOA formation
potential in China. Using published yield data and a surrogate equivalent
method, we estimated SOA formation under different OA (organic aerosol) loading and NO x 
conditions. Results showed that under low- and high-NO x conditions at
different OA loadings, IVOCs contributed more than 80 % of the predicted
SOA. Furthermore, we built up a parameterization method to simply estimate
the vehicular SOA based on our bottom-up measurement of VOCs (volatile organic compounds) and IVOCs,
which would provide another dimension of information when considering the
vehicular contribution to the ambient OA. Our results indicate that
vehicular IVOCs contribute significantly to SOA, implying the
importance of reducing IVOCs when making air pollution controlling policies
in urban areas of China.

/pdf/measurement-report-distinct-emissions-and-volatility-480t6mq9zw.pdf

Measurement report: Distinct emissions and volatility distribution of intermediate-volatility organic compounds from on-road Chinese gasoline vehicles: implication of high secondary organic aerosol formation potential

Characterizing chemical composition and light absorption of nitroaromatic compounds in the winter of Beijing

. Air pollution by particulate matter in China affects human health, the
ecosystem and the climate. However, the chemical composition of particulate
aerosol, especially of the organic fraction, is still not well understood.
In this study, particulate aerosol samples with a diameter of ≤2.5 µ m ( PM2.5 ) were collected in January 2014 in three cities located
in northeast, east and southeast China, namely Changchun, Shanghai and
Guangzhou. Organic aerosol (OA) in the PM2.5 samples was analyzed by an
ultrahigh-performance liquid chromatograph (UHPLC) coupled to
a high-resolution Orbitrap mass spectrometer in both negative mode (ESI-)
and positive mode electrospray ionization (ESI+). After non-target
screening including the assignment of molecular formulas, the compounds were
classified into five groups based on their elemental composition, i.e., CHO,
CHON, CHN, CHOS and CHONS. The CHO, CHON and CHN groups present the dominant
signal abundances of 81 %–99.7 % in the mass spectra and the majority of
these compounds were assigned to mono- and polyaromatics, suggesting that
anthropogenic emissions are a major source of urban OA in all three cities.
However, the chemical characteristics of these compounds varied between the
different cities. The degree of aromaticity and the number of polyaromatic
compounds were substantially higher in samples from Changchun, which could
be attributed to the large emissions from residential heating (i.e., coal
combustion) during wintertime in northeast China. Moreover, the ESI-
analysis showed higher H / C and O / C ratios for organic compounds in Shanghai
and Guangzhou compared to samples from Changchun, indicating that OA
undergoes more intense photochemical oxidation processes in lower-latitude
regions of China and/or is affected to a larger degree by biogenic sources.
The majority of sulfur-containing compounds (CHOS and CHONS) in all cities
were assigned to aliphatic compounds with low degrees of unsaturation and
aromaticity. Here again, samples from Shanghai and Guangzhou show a greater
chemical similarity but differ largely from those from Changchun. It should
be noted that the conclusions drawn in this study are mainly based on
comparison of molecular formulas weighted by peak abundance and thus are
associated with inherent uncertainties due to different ionization
efficiencies for different organic species.

/pdf/urban-organic-aerosol-composition-in-eastern-china-differs-10gim4rtb3.pdf

Urban organic aerosol composition in eastern China differs from north to south: molecular insight from a liquid chromatography–mass spectrometry (Orbitrap) study

Oxidative potential associated with water-soluble components of PM2.5 in Beijing: The important role of anthropogenic organic aerosols.

Naphthalene (Nap) and methylnaphthalene (MN) are the most abundant polycyclic aromatic hydrocarbons (PAHs) in atmosphere and have been proposed to be important precursors of anthropogenic secondary organic aerosol (SOA) derived from laboratory chamber experiments. In this study, atmospheric Nap/MN and their gas-phase photooxidation products were quantified by a Proton Transfer Reaction-Quadrupole interface Time-of-Flight Mass Spectrometer (PTR-QiTOF) during the 2016 winter in Beijing. Phthalic anhydride, a late generation product from Nap under high-NOx conditions, appeared to be more prominent than 2-formylcinnamaldehyde (early generation product), possibly due to more sufficient oxidation during the haze. 1,2-Phthalic acid (1,2-PhA), the hydrated form of phthalic anhydride, was capable of partitioning into aerosol phase and served as a tracer to explore the contribution of Nap to ambient SOA. The measured fraction in particle phase (Fp) of 1,2-PhA averaged at 73 ± 13% with OA mass loadings of 52.5–87.8 ...

Potentially Important Contribution of Gas-Phase Oxidation of Naphthalene and Methylnaphthalene to Secondary Organic Aerosol during Haze Events in Beijing.

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Potentially Important Contribution of Gas-Phase Oxidation of Naphthalene and Methylnaphthalene to Secondary Organic Aerosol during Haze Events in Beijing.