Showing papers by "Haiyan Ni published in 2021"
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TL;DR: In this article, the light absorption of brown carbon (BrC) from primary and photochemically aged coal combustion emissions was measured by the UV-visible spectrophotometric analysis of water and methanol extracts of filter samples.
Abstract: Smog chamber experiments were conducted to characterize the light absorption of brown carbon (BrC) from primary and photochemically aged coal combustion emissions. Light absorption was measured by the UV-visible spectrophotometric analysis of water and methanol extracts of filter samples. The single-scattering albedo at 450 nm was 0.73 ± 0.10 for primary emissions and 0.75 ± 0.13 for aged emissions. The light absorption coefficient at 365 nm of methanol extracts was higher than that of water extracts by a factor of 10 for primary emissions and a factor of 7 for aged emissions. This suggests that the majority of BrC is water-insoluble even after aging. The mass absorption efficiency of this BrC (MAE365) for primary OA (POA) was dependent on combustion conditions, with an average of 0.84 ± 0.54 m2 g-1, which was significantly higher than that for aged OA (0.24 ± 0.18 m2 g-1). Secondary OA (SOA) dominated aged OA and the decreased MAE365 after aging indicates that SOA is less light absorbing than POA and/or that BrC is bleached (oxidized) with aging. The estimated MAE365 of SOA (0.14 ± 0.08 m2 g-1) was much lower than that of POA. A comparison of MAE365 of residential coal combustion with other anthropogenic sources suggests that residential coal combustion emissions are among the strongest absorbing BrC organics.
25 citations
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TL;DR: In this paper, the chemical composition of particulate aerosol, especially of the organic fraction, is still not well understood, and the majority of these compounds were assigned to mono-and polyaromatics, suggesting that anthropogenic emissions are a major source of urban OA.
Abstract: . 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.
24 citations
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TL;DR: The chemical composition and sources of Nitrated aromatic compounds (NACs) and their contributions to BrC absorption were investigated for 112 daily PM 2.5 -bound NACs in Xi'an, Northwest China, were investigated in this paper.
Abstract: . Nitrated aromatic compounds (NACs) are a group of key chromophores for brown
carbon (light-absorbing organic carbon, i.e., BrC) aerosol, which affects
radiative forcing. The chemical composition and sources of NACs and their
contributions to BrC absorption, however, are still not well understood. In
this study, PM 2.5 -bound NACs in Xi'an, Northwest China, were
investigated for 112 daily PM 2.5 filter samples from 2015 to 2016. Both
the total concentrations and contributions from individual species of NACs
show distinct seasonal variations. The seasonally averaged concentrations of
NACs are 2.1 (spring), 1.1 (summer), 12.9 (fall), and 56 ng m −3
(winter). Thereinto, 4-nitrophenol is the major NAC component in spring
(58 %). The concentrations of 5-nitrosalicylic acid and 4-nitrophenol
dominate in summer (70 %), and the concentrations of 4-nitrocatechol and
4-nitrophenol dominate in fall (58 %) and winter (55 %). The NAC species
show different seasonal patterns in concentrations, indicating differences
in emissions and formation pathways. Source apportionment results using
positive matrix factorization (PMF) further show large seasonal differences
in the sources of NACs. Specifically, in summer, NACs were highly influenced
by secondary formation and vehicle emissions ( ∼ 80 %), while
in winter, biomass burning and coal combustion contributed the most
( ∼ 75 %). Furthermore, the light absorption contributions of
NACs to BrC are wavelength-dependent and vary greatly by season, with maximum contributions at ∼ 330 nm in winter and fall and
∼ 320 nm in summer and spring. The differences in the
contribution to light absorption are associated with the higher mass
fractions of 4-nitrocatechol ( λ max = 345 nm) and 4-nitrophenol
( λ max = 310 nm) in fall and winter, 4-nitrophenol in spring,
and 5-nitrosalicylic acid ( λ max = 315 nm) and 4-nitrophenol in
summer. The mean contributions of NACs to BrC light absorption at a
wavelength of 365 nm in different seasons are 0.14 % (spring), 0.09 %
(summer), 0.36 % (fall), and 0.91 % (winter), which are about 6–9 times
higher than their mass fractional contributions of carbon in total organic
carbon. Our results indicate that the composition and sources of NACs have
profound impacts on the BrC light absorption.
19 citations
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TL;DR: Investigation of SOA formation and evolution processes during summer in Xi'an found the persistently high RH period with high aerosol liquid water content (ALWC) was the driving factor of aq-OOA formation, and high Ox condition could further enhance its formation.
18 citations
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TL;DR: In this article, the mass concentration and optical properties of Humic-like substances (HULIS) isolated from aerosol samples collected in Xi'an, China were analyzed by positive matrix factorization (PMF) and four major sources were resolved.
9 citations
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TL;DR: In this article, the authors present 13C signatures of organic carbon (OC) and elemental carbon (EC) for relevant sources in China, which are used to apportion the main sources of EC (C3/C4 plant burning, coal combustion, and traffic emissions).
4 citations