Intensive agricultural activities in the North China Plain (NCP) lead to substantial emissions of nitrogen oxides (NO
) from soil, while the role of this source on local severe ozone pollution is ...unknown. Here we use a mechanistic parameterization of soil NO
emissions combined with two atmospheric chemistry models to investigate the issue. We find that the presence of soil NO
emissions in the NCP significantly reduces the sensitivity of ozone to anthropogenic emissions. The maximum ozone air quality improvements in July 2017, as can be achieved by controlling all domestic anthropogenic emissions of air pollutants, decrease by 30% due to the presence of soil NO
. This effect causes an emission control penalty such that large additional emission reductions are required to achieve ozone regulation targets. As NO
emissions from fuel combustion are being controlled, the soil emission penalty would become increasingly prominent and shall be considered in emission control strategies.
China’s nationwide ozone monitoring network initiated in 2013 has observed severe surface ozone pollution. This network, combined with the recent Tropospheric Ozone Assessment Report (TOAR) data set, ...offers a more comprehensive view on global surface ozone distribution and trends. Here, we report quantitative estimates of the warm-season (April–September) surface ozone trends and resulting health impacts at Chinese cities in 2013–2019. Both the parametric and nonparametric linear trends for 12 ozone metrics relevant to human health and vegetation exposure are derived. We find that all ozone metrics averaged from Chinese urban sites have increased significantly since 2013. The warm-season daily maximum 8-h average (MDA8) ozone levels increased by 2.4 ppb (5.0%) year–1, with over 90% of the sites showing positive trends and 30% with trends larger than 3.0 ppb year–1. These rates are among the fastest trends, even faster in some Chinese cities, compared with the urban ozone trends in any other region worldwide reported in TOAR. Ozone metrics reflecting the cumulative exposure effect on human health and vegetation such as SOMO35 and AOT40 have increased at even faster rates (>10% year–1). We estimate that the total premature respiratory mortalities attributable to ambient MDA8 ozone exposure in 69 Chinese cities are 64,370 in 2019, which has increased by 60% compared to 2013 levels and requires urgent attention.
Heterogeneous reactions of mineral dust aerosol with trace gases in the atmosphere could directly and indirectly affect tropospheric oxidation capacity, in addition to aerosol composition and ...physicochemical properties. In this article we provide a comprehensive and critical review of laboratory studies of heterogeneous uptake of OH, NO3, O3, and their directly related species as well (including HO2, H2O2, HCHO, HONO, and N2O5) by mineral dust particles. The atmospheric importance of heterogeneous uptake as sinks for these species is assessed (i) by comparing their lifetimes with respect to heterogeneous reactions with mineral dust to lifetimes with respect to other major loss processes and (ii) by discussing relevant field and modeling studies. We have also outlined major open questions and challenges in laboratory studies of heterogeneous uptake by mineral dust and discussed research strategies to address them in order to better understand the effects of heterogeneous reactions with mineral dust on tropospheric oxidation capacity.
This paper presents the pollution levels, variation characteristics, chemical reactivity, source apportionment and potential source regions of 102 volatile organic compounds (VOCs) observed from ...2017.4.26 to 2017.6.6 in urban Wuhan. The concentration of total VOCs (TVOCs) was 28.92 ± 20.10 ppbv, and the VOC composition was dominated by alkanes (51.14%). Propane, ethane and acetone were the most abundant VOC species. The results for the OH radical loss rate (LOH) and ozone formation potential (OFP) indicated that alkenes were responsible for much of the chemical reactivity and O3 formation, accounting for 47.02% and 49.52%, respectively, and the dominant VOC species were mainly associated with anthropogenic sources, such as vehicle emissions, the use of natural gas (NG) and liquefied petroleum gas (LPG), solvent usage and fuel evaporation. Ambient ratio data showed that VOCs were greatly affected by the pollution sources (such as emissions of NG and LPG, liquid gasoline and fuel evaporation sources, vehicle exhaust emissions, and biogenic sources), photochemical reaction processes and regional transport. Industrial sources (11.84%), industrial sources + coal burning (13.09%), LPG/NG usage + solvent usage in painting/coating (37.28%), fuel evaporation (12.04%), vehicle exhaust (13.65%), biogenic sources (5.95%) and biomass burning (6.15%) were determined by positive matrix factorization (PMF). Furthermore, LPG/NG usage, solvent usage in painting/coating and vehicle exhaust were the most important VOC sources, and their various contributions were affected by a combination of factors, including the emission strength of pollution sources, meteorological conditions and photochemical reaction processes. Backward trajectory analysis showed that VOC pollution was mainly derived from the south via short-distance transport. The potential source contribution function (PSCF) results indicated that the main sources affecting VOC pollution were the potential sources to the south and local sources within the city. This study provides evidence for local governments to formulate VOC control strategies during the transition from spring to summer.
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•Alkenes were the key components of chemical reactivity and O3 formation.•The effects of sources, photochemical reactions and air mass on VOCs were analysed.•LPG/NG usage, solvent usage in painting/coating and vehicle exhaust were important.•Potential sources from the south and local sources within the city were important.
For a quasinilpotent operator
T
on a separable Hilbert space
H
, Douglas and Yang define
k
x
=
lim sup
λ
→
0
ln
‖
(
λ
-
T
)
-
1
x
‖
ln
‖
(
λ
-
T
)
-
1
‖
for each nonzero vector
x
, and call
Λ
(
T
)
=
...{
k
x
:
x
≠
0
}
the
power set
of
T
. In this paper, we prove that
Λ
(
T
)
is right closed, that is,
sup
σ
∈
Λ
(
T
)
for each nonempty subset
σ
of
Λ
(
T
)
. Moreover, for any right closed subset
σ
of 0, 1 containing 1, we show that there exists a quasinilpotent operator
T
with
Λ
(
T
)
=
σ
. Finally, we prove that the power set of
V
, the Volterra operator on
L
2
0
,
1
, is (0, 1.
Accurate determination of the atmospheric particulate matter mass concentration and chemical composition is helpful in exploring the causes and sources of atmospheric enthalpy pollution and in ...evaluating the rationality of environmental air quality control strategies. Based on the sampling and chemical composition data of PM
2.5
in different key regions of China in the CARE-China observation network, this research analyzes the environmental air quality data released by the China National Environmental Monitoring Centre during the studied period to determine the changes in the particulate matter mass concentration in key regions and the evolution of the corresponding chemical compositions during the implementation of the
Action Plan for Prevention and Control of Air Pollution
from 2013–2017. The results show the following. (1) The particulate matter mass concentration in China showed a significant downward trend; however, the PM
2.5
annual mass concentration in 64% of cities exceeds the New Chinese Ambient Air Quality Standard (CAAQS) Grade II (GB3095-2012). The region to the east of the Taihang Mountains, the Fenhe and Weihe River Plain and the Urumqi-Changji regions in Xinjiang, all have PM
2.5
concentration loading that is still high, and heavy haze pollution occurred frequently in the autumn and winter. (2) During the heavy pollution in the autumn and winter, the concentrations of sulfate and organic components decreased significantly. The mean
S
O
4
2
−
concentration in PM
2.5
decreased by 76%, 12%, 81% and 38% in Beijing-Tianjin-Hebei (BTH), the Pearl River Delta (PRD), the Sichuan-Chongqing region (SC) and the Fenhe and Weihe River Plain, respectively. The mean organic matter (OM) concentration decreased by 70%, 44%, 48% and 31%, respectively, and the mean concentration of
N
H
4
+
decreased by 68%, 1.6%, 38% and 25%, respectively. The mean elemental carbon (EC) concentration decreased by 84% and 20% in BTH and SC, respectively, and it increased by 61% and 11% in the PRD and Fenhe and Weihe River Plain, respectively. The mean concentration of mineral and unresolved chemical components (MI) dropped by 70%, 24% and 13% in BTH, the PRD and the Fenhe and Weihe River Plain, respectively. The change in the PM
2.5
chemical composition is consistent with the decrease of the PM
2.5
mass concentration. (3) In 2015, the mean OM concentration contributions to fine particles and coarse particles were 13–46% and 46–57%, respectively, and the mean MI concentration contributions to fine particles and coarse and particles were 31–60% and 39–73%, respectively; these values are lower than the 2013 values from the key regions, which is the most important factor behind the decrease of the particulate matter mass concentration. From 2013 to 2015, among the chemical components of different particle size fractions, the peak value of the coarse particle size fraction decreased significantly, and the fine particle size fractions of
S
O
4
2
−
,
N
O
4
−
,
a
n
d
N
H
4
+
decreased with the decrease of the particulate matter mass concentration in different particle size fractions. The fine-particle size peaks of
S
O
4
2
−
,
N
O
4
−
,
a
n
d
N
H
4
+
shifted from 0.65–1.1 μm to the finer size range of 0.43–0.65 μm during the same time frame.
Long and deep tunnels are increasingly designed and built worldwide, often in severe geothermal environments characterized by high temperature in the rocks. This issue cannot be ignored because high ...temperature definitely affects the strength of the adhesion between the concrete and the surrounding rocks, whatever the lining cast in place, segmental or sprayed using shotcrete. The causes of geothermal heat and the effect of the temperature on tunnel linings during and after their construction are recalled and discussed in this paper. Both temperature and humidity are shown to be the most relevant factors affecting adhesion strength, whose loss is related to the microdamage in the shotcrete layers closest to the rock. Possible ways to improve adhesion strength and to minimize the high-temperature detrimental effect are also presented and discussed.
From technical and economical viewpoints, an all‐dc offshore wind farm (OWF) with a high‐voltage direct‐current (HVDC) connection, which is also known as HVDC‐connected all‐dc OWF, is the future ...trend for offshore wind energy applications. However, due to the decoupling effect of power converters, all‐dc OWF cannot directly provide short‐term frequency support for the onshore ac gird, that is, primary frequency response and inertia support. To address this issue, this paper presents a distributed model predictive control (DMPC) scheme for all‐dc OWF. By directly suppressing the voltage deviation and the rate of change of voltage of the offshore dc collection network, this scheme indirectly decreases the frequency deviation and the rate of change of frequency (RoCoF) of the onshore ac grid. Meanwhile, the scheme ensures the stability of wind turbines in all‐dc OWF during the frequency events. Considering a large number of wind turbines in the OWF, the corresponding optimization problem is solved in a distributed way using the alternating direction method of multipliers (ADMM), thus reducing the computational burden. Simulations including the performance comparison with droop control validate the effectiveness of this scheme.
In contrast to summer smog, the contribution of photochemistry to the formation of winter haze in northern mid-to-high latitude is generally assumed to be minor due to reduced solar UV and water ...vapor concentrations. Our comprehensive observations of atmospheric radicals and relevant parameters during several haze events in winter 2016 Beijing, however, reveal surprisingly high hydroxyl radical oxidation rates up to 15 ppbv/h, which is comparable to the high values reported in summer photochemical smog and is two to three times larger than those determined in previous observations during winter in Birmingham (Heard et al. Geophys. Res. Lett. 2004, 31, (18)), Tokyo (Kanaya et al. J. Geophys. Res.: Atmos. 2007, 112, (D21)), and New York (Ren et al. Atmos. Environ. 2006, 40, 252–263). The active photochemistry facilitates the production of secondary pollutants. It is mainly initiated by the photolysis of nitrous acid and ozonolysis of olefins and maintained by an extremely efficiently radical cycling process driven by nitric oxide. This boosted radical recycling generates fast photochemical ozone production rates that are again comparable to those during summer photochemical smog. The formation of ozone, however, is currently masked by its efficient chemical removal by nitrogen oxides contributing to the high level of wintertime particles. The future emission regulations, such as the reduction of nitrogen oxide emissions, therefore are facing the challenge of reducing haze and avoiding an increase in ozone pollution at the same time. Efficient control strategies to mitigate winter haze in Beijing may require measures similar as implemented to avoid photochemical smog in summer.
Daily PM2.5 samples were collected at an urban site in Beijing during four one-month periods in 2009–2010, with each period in a different season. Samples were subject to chemical analysis for ...various chemical components including major water-soluble ions, organic carbon (OC) and water-soluble organic carbon (WSOC), element carbon (EC), trace elements, anhydrosugar levoglucosan (LG), and mannosan (MN). Three sets of source profiles of PM2.5 were first identified through positive matrix factorization (PMF) analysis using single or combined biomass tracers — non-sea salt potassium (nss-K+), LG, and a combination of nss-K+ and LG. The six major source factors of PM2.5 included secondary inorganic aerosol, industrial pollution, soil dust, biomass burning, traffic emission, and coal burning, which were estimated to contribute 31±37%, 39±28%, 14±14%, 7±7%, 5±6%, and 4±8%, respectively, to PM2.5 mass if using the nss-K+ source profiles, 22±19%, 29±17%, 20±20%, 13±13%, 12±10%, and 4±6%, respectively, if using the LG source profiles, and 21±17%, 31±18%, 19±19%, 11±12%, 14±11%, and 4±6%, respectively, if using the combined nss-K+ and LG source profiles. The uncertainties in the estimation of biomass burning contributions to WSOC due to the different choices of biomass burning tracers were around 3% annually and up to 24% seasonally in terms of absolute percentage contributions, or on a factor of 1.7 annually and up to a factor of 3.3 seasonally in terms of the actual concentrations. The uncertainty from the major source (e.g. industrial pollution) was on a factor of 1.9 annually and up to a factor of 2.5 seasonally in the estimated WSOC concentrations.
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•Various biomass burning tracers were compared.•PM2.5 source profiles were compared using different biomass burning tracers.•Uncertainties in source attribution of PM2.5 and WSOC were quantified.
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