PM2.5 concentrations have
decreased remarkably in China
in recent years, coinciding with a more rapid decrease in SO2 concentrations and a slower decrease in NO2 concentrations,
while O3 concentrations increased. Correlations between
PM2.5 and key gaseous pollutants were studied to identify
linked trends as a means of understanding the impacts of air pollution
control in China. In most cities, the PM2.5–NO2 correlation coefficients were higher than the PM2.5–SO2 correlation coefficients, and the gap tended
to expand as air quality improved. Multiple linear regression also
indicated that PM2.5 concentrations were more sensitive
to changes in NO2 than in SO2. The rate of decrease
in the PM2.5 concentration with a decreasing NO2 concentration is nearly 3 times higher than that with SO2. These results support the priority of controlling NO
x
to further reduce PM2.5 pollution in
China. The chemistry behind this was twofold: (1) NO
x
can be converted into nitrate, and (2) NO
x
contributes to atmospheric oxidation capacity. The decrease
in PM2.5 concentration always coincided with an increase
in O3 concentration when the PM2.5 concentration
was higher than 50 μg m–3. However, the correlation
between PM2.5 and O3 tended to change from negative
to positive as air quality improved, indicating O3 and
PM2.5 control could both benefit from reducing the concentrations
of gas precursors.
Rigid macrocycles 2, which share a hybrid backbone and the same set of side chains while having inner cavities with different inward-pointing functional groups, undergo similar nanotubular assembly as indicated by multiple techniques including (1)H NMR, fluorescence spectroscopy, and atomic force microscopy. The formation of tubular assemblies containing subnanometer pores is also attested by the different transmembrane ion-transport behavior observed for these macrocycles. Vesicle-based stopped-flow kinetic assay and single-channel electrophysiology with planar lipid bilayers show that the presence of an inward-pointing functional (X) group in the inner cavity of a macrocyclic building block exerts a major influence on the transmembrane ion-transporting preference of the corresponding self-assembling pore. Self-assembling pores with inward-pointing amino and methyl groups possess the surprising and remarkable capability of rejecting protons but are conducive to transporting larger ions. The inward-pointing groups also resulted in transmembrane pores with a different extent of positive electrostatic potentials, leading to channels having different preferences for transporting chloride ion. Results from this work demonstrate that synthetic modification at the molecular level can profoundly impact the property of otherwise structurally persistent supramolecular assemblies, with both expected tunability and suprisingly unusual behavior.
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