[Water-soluble Inorganic Ion Content of PM2.5 and Its Change Characteristics in Urban Area of Beijing in 2022].

To explore the content and variation characteristics of water-soluble ions of atmospheric fine particles (PM2.5) in a Beijing urban area and put forward the pollution prevention and control scheme, the water-soluble ions, gaseous precursors (SO2, NO2), and meteorological factors (temperature, RH) of PM2.5 in 2022 were analyzed and determined. The results showed that the water-soluble ions with the highest proportion in PM2.5 in the Beijing City urban area were NO3-, NH4+, and SO42-, accounting for 52.7% of PM2.5. The mass concentrations of PM2.5 and SNA were lower than the historical results, whereas the proportion of SNA, SOR, and NOR was higher than the historical results. This showed that the fine particulate matter pollution in Beijing has been significantly improved, but it still has strong secondary pollution characteristics. NO3-/SO42-(2.2) was higher than those of historical and nearby provinces and cities, reflecting the expanding influence of mobile sources. In terms of seasonal variation, PM2.5 showed the characteristic of high in autumn and low in summer. The proportion of NO3- was the highest in autumn, spring, and winter; the proportion of SO42- was the highest in summer; and the proportion of NH4+ changed little in each season. The seasonal variation rules of NOR and SOR were almost opposite, which reflected the difference in transformation factors between NOR and SOR. The main forms of SNA in the Beijing urban area were NH4NO3 and (NH4)2SO4. The neutralization degree of cations and anions was the highest in winter, the cation NH4+ was slightly insufficient in summer, and NH4+ was in excess in spring and autumn. The Beijing urban area was an ammonia-rich environment. In terms of pollution level, RH, particulate matter moisture, and water-soluble ions mass concentration all increased with the increase in pollution level, and SNA increased fastest, with its proportion in PM2.5 increasing first and then stabilizing, whereas the contribution rate of other water-soluble ions decreased gradually. In terms of spatial distribution, the mass concentration relationship of SNA at the central urban area and suburbs was NO3- > SO42- > NH4+, which reflected the pollution characteristics dominated by NO3-. The highest contribution rate of SNA to PM2.5 occurred in the eastern region, the central urban area, and the transmission point, indicating that the secondary reaction was relatively active in the central urban area and the eastern region, and the regional transport was also an important source of secondary ions.

Primary organic gas emissions from gasoline vehicles in China: Factors, composition and trends.

Continuous tightening emission standards (ESs) facilitate the reduction of organic gas emissions from gasoline vehicles. Correspondingly, it is essential to update the emissions and chemical speciation of total organic gases (TOGs), including volatile organic compounds (VOCs), intermediate volatility organic compounds (IVOCs), CH4, and unidentified non-methane hydrocarbons (NMHCs) for assessing the formation of ozone and secondary organic aerosol (SOA). In this study, TOG and speciation emissions from 12 in-use light-duty gasoline vehicle (LDGV) exhausts, covering the ESs from China II to China V, were investigated on a chassis dynamometer under the Worldwide Harmonized Light-duty Test Cycle (WLTC) in China. The results showed that the most effectively controlled subgroup in TOG emissions from LDGVs was VOCs, followed by the unidentified NMHCs and IVOCs. The mass fraction of VOCs in TOGs also reduced from 61 ± 9% to 46 ± 18% while the IVOCs gently increased from 2 ± 0.4% to 8 ± 4% along with the more stringent ESs. For the VOC subsets, the removal efficiency of oxygenated VOCs (OVOCs) was lower than those of other VOC subsets in the ESs from China IV to V, suggesting the importance of OVOC emission controls for relatively new LDGVs. The IVOC emissions were mainly subject to the ESs, then driving cycles and fuel use. The formation potentials of ozone and SOA from LDGVs decreased separately 96% and 90% along with the restricted ESs from China II-III to China IV. The major contributor of SOA formation transformed from aromatics in the VOC subsets for China II-III vehicles to IVOCs for China IV/V vehicles, highlighting that IVOC emissions from LDGVs are also needed more attentions to control in future.

Intermediate-Volatility Organic Compound Emissions from Nonroad Construction Machinery under Different Operation Modes.

Intermediate-volatility organic compounds (IVOCs) have been found as important sources for secondary organic aerosol (SOA) formation. IVOC emissions from nonroad construction machineries (NRCMs), including two road rollers and three motor graders, were characterized under three operation modes using an improved portable emission measurement system. The fuel-based IVOC emission factors (EFs) of NRCMs varied from 245.85 to 1802.19 mg/kg·fuel, which were comparable at magnitudes to the reported results of an ocean-going ship and on-road diesel vehicles without filters. The discrepancy of IVOC EFs is significant within different operation modes. IVOC EFs under the idling mode were 1.24-3.28 times higher than those under moving/working modes. Unspeciated b-alkanes and cyclic compounds, which were the unresolved components in IVOCs at the molecular level, accounted for approximately 91% of total IVOCs from NRCMs. The SOA production potential analysis shows that IVOCs dominated SOA formation of NRCMs. Our results demonstrate that IVOC emissions from NRCMs are non-negligible. Thus, an accurate estimation of their IVOC emissions would benefit the understanding of SOA formation in the urban atmosphere.

Adsorption kinetics, isotherms and thermodynamics of atrazine on surface oxidized multiwalled carbon nanotubes.

The adsorption kinetics, isotherms and thermodynamic of atrazine on multiwalled carbon nanotubes (MWCNTs) containing 0.85%, 2.16%, and 7.07% oxygen was studied. Kinetic analyses were performed using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The regression results showed that the pseudo-second-order law fit the adsorption kinetics. The calculated thermodynamic parameters indicated that adsorption of atrazine on MWCNTs was spontaneous and exothermic. Standard free energy (DeltaG(0)) became less negative when the oxygen content of MWCNTs increased from 0.85% to 7.07% which is consistent with the low adsorption affinity of MWCNTs for atrazine.

Kinetics and thermodynamics of sorption of nitroaromatic compounds to as-grown and oxidized multiwalled carbon nanotubes.

The sorption kinetics and thermodynamics of 1,3-dinitrobenzene (DNB), m-nitrotoluene (mNT), p-nitrophenol (pNP), and nitrobenzene (NB) on as-grown and nitric acid-oxidized multiwalled carbon nanotubes (MWCNTs) were investigated. The sorption kinetics was well described by a pseudo-second-order rate model, while both Langmuir and Freundlich models described the sorption isotherms well and the sorption thermodynamic parameters of equilibrium constant (K(0)), standard free energy (DeltaG), standard enthalpy (DeltaH), and standard entropy changes (DeltaS) were measured. The values of DeltaH and DeltaG suggested that the sorption of nitroaromatics (NACs) onto MWCNTs was exothermic and spontaneous. The structure, number, and position of nitro groups of NACs were the main factors affecting the sorption rate and capacity. Treatment of the MWCNTs with nitric acid increased both the surface area and the pore volume and introduced oxygen-containing functional groups to the MWCNTs, which depressed the sorption of NACs onto MWCNTs.

Effects of copper, lead, and cadmium on the sorption and desorption of atrazine onto and from carbon nanotubes.

There are currently few studies on the dual effects of metal ions on the sorption of atrazine and conversely of atrazine on metal adsorption on multiwalled carbon nanotubes (MWCNTs). While a number of sorption models were considered to describe the sorption of atrazine on MWCNTs, the Polanyi-Manes model (PMM) fit the sorption isotherms well with the lowest mean weighted square errors. Atrazine was mainly adsorbed onto the surface and micropores of MWCNTs bundles or aggregates. Hydrogen bonding between azo and amino nitrogen of atrazine and functional groups on MWCNTs also occurred. Oxygenated functionalities, mainly carboxylic groups on MWCNTs surface, decreased the sorption of atrazine. Metal cations Cu2+, Pb2+, and Cd2+ diminished the sorption of atrazine depending on the oxygenated functionalities densities. The mechanisms ascribed were due to the formation of surface or inner-sphere complexes of Cu2+, Pb2+, and Cd2+ through carboxylic groups and hydration, which may occupy part of the surface of MWCNTs-O. The large hydration shell of metal cations may intrude or shield the hydrophobic and hydrophilic sites and indirectly compete with atrazine for surface sites, leading to the inhibition of atrazine adsorption around the metal-complexed moieties.