Association between psychological stress, anxiety and oral health status among college students during the Omicron wave: a cross-sectional study.

BACKGROUND: Within 3 years of the COVID-19 pandemic, increasing interest has been given to its potential influence on health status due to lockdowns caused by the pandemic. However, the impact is inadequately understood, especially for college students. This study aimed to investigate the potential association between psychological stress, anxiety and oral health of college students during the Omicron wave of the COVID-19 pandemic. METHODS: An online survey with measurements of psychological stress, anxiety and oral health was completed by 1770 Chinese college students. The Perceived Stress Scale-14 (PSS-14) and Generalized Anxiety Disorder-7 (GAD-7) were used to measure psychological stress and anxiety, respectively. Oral health status was self-reported including toothache, gingival bleeding, and oral ulcer. Multivariable logistic regressions were performed to determine underlying associations for outcome variables. Structural equation modeling (SEM) was performed to confirm the relationship between mental and oral health status. RESULTS: Of the 1770 subjects, 39.2% presented high psychological stress and only 41.2% expressed no anxiety. A significant association was found between psychological stress, anxiety and oral health status. Anxiety has significant impacts on toothache (OR = 0.36; 95%CI: 0.23-0.55; p < 0.01), gingival bleeding (OR = 0.43; 95%CI: 0.29-0.65; p < 0.01), and oral ulcer (OR = 0.54; 95%CI: 0.36-0.80; p < 0.01). Anxiety significantly mediated the association between psychological stress and self-reported oral symptoms. CONCLUSIONS: Anxiety may be a significant risk indicator for mental health among college students and demonstrates a significant relationship with the occurrence of self-reported oral symptoms. Concerns about academic and life changes caused by the pandemic were the two most significant sources of stress.

Changes in visibility with PM2.5 composition and relative humidity at a background site in the Pearl River Delta region.

In fall-winter, 2007-2013, visibility and light scattering coefficients (bsp) were measured along with PM2.5 mass concentrations and chemical compositions at a background site in the Pearl River Delta (PRD) region. The daily average visibility increased significantly (p<0.01) at a rate of 1.1 km/year, yet its median stabilized at ~13 km. No haze days occurred when the 24-hr mean PM2.5 mass concentration was below 75 µg/m(3). By multiple linear regression on the chemical budget of particle scattering coefficient (bsp), we obtained site-specific mass scattering efficiency (MSE) values of 6.5 ± 0.2, 2.6 ± 0.3, 2.4 ± 0.7 and 7.3 ± 1.2m(2)/g, respectively, for organic matter (OM), ammonium sulfate (AS), ammonium nitrate (AN) and sea salt (SS). The reconstructed light extinction coefficient (bext) based on the Interagency Monitoring of Protected Visual Environments (IMPROVE) algorithm with our site-specific MSE revealed that OM, AS, AN, SS and light-absorbing carbon (LAC) on average contributed 45.9% ± 1.6%, 25.6% ± 1.2%, 12.0% ± 0.7%, 11.2% ± 0.9% and 5.4% ± 0.3% to light extinction, respectively. Averaged bext displayed a significant reduction rate of 14.1/Mm·year (p<0.05); this rate would be 82% higher if it were not counteracted by increasing relative humidity (RH) and hygroscopic growth factor (f(RH)) at rates of 2.5% and 0.16/year(-1) (p<0.01), respectively, during the fall-winter, 2007-2013. This growth of RH and f(RH) partly offsets the positive effects of lowered AS in improving visibility, and aggravated the negative effects of increasing AN to impair visibility.

Organosulfates from pinene and isoprene over the Pearl River Delta, South China: seasonal variation and implication in formation mechanisms.

Biogenic organosulfates (OSs) are important markers of secondary organic aerosol (SOA) formation involving cross reactions of biogenic precursors (terpenoids) with anthropogenic pollutants. Until now, there has been rare information about biogenic OSs in the air of highly polluted areas. In this study, fine particle (PM2.5) samples were separately collected in daytime and nighttime from summer to fall 2010 at a site in the central Pearl River Delta (PRD), South China. Pinene-derived nitrooxy-organosulfates (pNOSs) and isoprene-derived OSs (iOSs) were quantified using a liquid chromatograph (LC) coupled with a tandem mass spectrometer (MS/MS) operated in negative electrospray ionization (ESI) mode. The pNOSs with MW 295 exhibited higher levels in fall (151 ± 86.9 ng m(-3)) than summer (52.4 ± 34.0 ng m(-3)), probably owing to the elevated levels of NOx and sulfate in fall when air masses mainly passed through city clusters in the PRD and biomass burning was enhanced. In contrast to observations elsewhere where higher levels occurred at nighttime, pNOS levels in the PRD were higher during the daytime in both seasons, indicating that pNOS formation was likely driven by photochemistry over the PRD. This conclusion is supported by several lines of evidence: the specific pNOS which could be formed through both daytime photochemistry and nighttime NO3 chemistry exhibited no day-night variation in abundance relative to other pNOS isomers; the production of the hydroxynitrate that is the key precursor for this specific pNOS was found to be significant through photochemistry but negligible through NO3 chemistry based on the mechanisms in the Master Chemical Mechanism (MCM). For iOSs, 2-methyltetrol sulfate ester which could be formed from isoprene-derived epoxydiols (IEPOX) under low-NOx conditions showed low concentrations (below the detection limit to 2.09 ng m(-3)), largely due to the depression of IEPOX formation by the high NOx levels over the PRD.

Compositions and sources of organic acids in fine particles (PM2.5) over the Pearl River Delta region, South China.

Organic acids as important constituents of organic aerosols not only influence the aerosols' hygroscopic property, but also enhance the formation of new particles and secondary organic aerosols. This study reported organic acids including C14-C32 fatty acids, C4-C9 dicarboxylic acids and aromatic acids in PM2.5 collected during winter 2009 at six typical urban, suburban and rural sites in the Pearl River Delta region. Averaged concentrations of C14-C32 fatty acids, aromatic acids and C4-C9 dicarboxylic acids were 157, 72.5 and 50.7 ng/m3, respectively. They totally accounted for 1.7% of measured organic carbon. C20-C32 fatty acids mainly deriving from higher plant wax showed the highest concentration at the upwind rural site with more vegetation around, while C14-C18 fatty acids were more abundant at urban and suburban sites, and dicarboxylic acids and aromatic acids except 1,4-phthalic acid peaked at the downwind rural site. Succinic and azelaic acid were the most abundant among C4-C9 dicarboxylic acids, and 1,2-phthalic and 1,4-phthalic acid were dominant aromatic acids. Dicarboxylic acids and aromatic acids exhibited significant mutual correlations except for 1,4-phthalic acid, which was probably primarily emitted from combustion of solid wastes containing polyethylene terephthalate plastics. Spatial patterns and correlations with typical source tracers suggested that C14-C32 fatty acids were mainly primary while dicarboxylic and aromatic acids were largely secondary. Principal component analysis resolved six sources including biomass burning, natural higher plant wax, two mixed anthropogenic and two secondary sources; further multiple linear regression revealed their contributions to individual organic acids. It turned out that more than 70% of C14-C18 fatty acids were attributed to anthropogenic sources, about 50%-85% of the C20-C32 fatty acids were attributed to natural sources, 80%-95% of dicarboxylic acids and 1,2-phthalic acid were secondary in contrast with that 81% of 1,4-phthalic acid was primary.

Ionic composition of submicron particles (PM1.0) during the long-lasting haze period in January 2013 in Wuhan, central China.

In January 2013, a long-lasting severe haze episode occurred in Northern and Central China; at its maximum, it covered a land area of approximately 1.4 million km(2). In Wuhan, the largest city in Central China, this event was the most severe haze episode in the 21st century. Aerosol samples of submicron particles (PM1.0) were collected during the long-lasting haze episode at an urban site and a suburban site in Wuhan to investigate the ion characteristics of PM1.0 in this area. The mass concentrations of PM1.0 and its water-soluble inorganic ions (WSIIs) were almost at the same levels at two sites, which indicates that PM1.0 pollution occurs on a regional scale in Wuhan. WSIIs (Na(+), NH4(+), K(+), Mg(2+), Ca(2+), Cl(-), NO3(-) and SO4(2-)) were the dominant chemical species and constituted up to 48.4% and 47.4% of PM1.0 at WD and TH, respectively. The concentrations of PM1.0 and WSIIs on haze days were approximately two times higher than on normal days. The ion balance calculations indicate that the particles were more acidic on haze days than on normal days. The results of the back trajectory analysis imply that the high concentrations of PM1.0 and its water-soluble inorganic ions may be caused by stagnant weather conditions in Wuhan.

Secondary inorganic aerosols and aerosol acidity at different PM2.5 pollution levels during winter haze episodes in the Sichuan Basin, China.

Wintertime fine particle (PM2.5) pollution remains to be perplexing air quality problems in many parts of China. In this study, PM2.5 compositions and aerosol acidity at different pollution levels at an urban cite in the southwest China's Sichuan Basin were investigated during a sustained winter haze episode. Organic matter was the most abundant component of PM2.5, followed by nitrate, sulfate and ammonium. Shares of organic aerosol in PM2.5 mass decreased with the elevated PM2.5 levels, while the enhancements of sulfate and secondary organic aerosol were much less than that of nitrate and ammonium during heavy pollution with increased ratios of nitrate to sulfate, implying a significant role of nitrate in the haze formation. Results also suggest the nighttime chemistry might contribute substantially to the formation of nitrate under severe pollutions. The daily average aerosol pH showed a decreasing trend with the elevated levels of PM2.5, and this increased aerosl acidity was mainly due to the fast rising secondary inorganic aerosol (SIA) concentration, with the increase in hydronium ion concentration in air (Hair+) surpassing the dilution effect of elevated aerosol liquid water content (LWC). Thermodynamic model calculations revealed that the air environment was NH3-rich with total NHx (NH3 + NH4+) greater than required NHx, and the aerosol pH exponentially declined with the decreasing excess NHx (p < 0.01). This study demonstrated that under air stagnation and NH3-rich environment during winter, the raised relative humidity (RH) would lead to an increase in LWC and thereby facilitate the aqueous chemistry processes with the neutralization capacity of NH3 to form sulfate and nitrate, which would further increase the LWC and lower the pH. This self-amplifying SIA formation might be crucial to the severe PM2.5 pollution and haze events during winter, and therefore cutting both NOx and NH3 emissions would benefit stopping the self-amplification.

Aerosol scattering coefficients and major chemical compositions of fine particles observed at a rural site in the central Pearl River Delta, south China.

During November-December 2010 aerosol scattering coefficients were monitored using a single-waved (525 nm) Nephelometer at a regional monitoring station in the central Pearl River Delta region and 24-hr fine particle (PM2.5) samples were also collected during the period using quartz filters for the analysis of major chemical components including organic carbon (OC), elemental carbon (EC), sulfate, nitrate and ammonium. In average, these five components accounted for about 85% of PM2.5 mass and contributed 42% (OC), 19% (SO4(2-)), 12% (NO(3-)), 8.4% (NH(4+)) and 3.7% (EC), to PM2.5 mass. A relatively higher mass scattering efficiency of 5.3 m2/g was obtained for fine particles based on the linear regression between scattering coefficients and PM2.5 mass concentrations. Chemical extinction budget based on IMPROVE approach revealed that ammonium sulfate, particulate organic matter, ammonium nitrate and EC in average contributed about 32%, 28%, 20% and 6% to the light extinction coefficients, respectively.

Filter-based measurement of light absorption by brown carbon in PM2.5 in a megacity in South China.

Carbonaceous aerosols represent an important nexus between air pollution and climate change. Here we collected filter-based PM2.5 samples during summer and autumn in 2015 at one urban and two rural sites in Guangzhou, a megacity in southern China, and got the light absorption by black carbon (BC) and brown carbon (BrC) resolved with a DRI Model 2015 multi-wavelength thermal/optical carbon analyzer apart from determining the organic carbon (OC) and elemental carbon (EC) contents. On average BrC contributed 12-15% of the measured absorption at 405nm (LA405) during summer and 15-19% during autumn with significant increase in the LA405 by BrC at the rural sites. Carbonaceous aerosols, identified as total carbon (TC), yielded average mass absorption efficiency at 405nm (MAE405) that were approximately 45% higher in autumn than in summer, an 83% increase was noted in the average MAE405 for OC, compared with an increase of only 14% in the average MAE405 for EC. The LA405 by BrC showed a good correlation (p<0.001) with the ratios of secondary OC to PM2.5 in summer. However, this correlation was poor (p>0.1) in autumn, implying greater secondary formation of BrC in summer. The correlations between levoglucosan (a marker of biomass burning) and the LA405 by BrC were significant during autumn but insignificant during summer, suggesting that the observed increase in the LA405 by BrC during autumn in rural areas was largely related to biomass burning. The measurements of light absorption at 550nm presented in this study indicated that the use of the IMPROVE algorithm with an MAE value of 10m2/g for EC to approximate light absorption may be appropriate in areas not strongly affected by fossil fuel combustion; however, this practice would underestimate the absorption of light by PM2.5 in areas heavily affected by vehicle exhausts and coal burning.

PM2.5 acidity at a background site in the Pearl River Delta region in fall-winter of 2007-2012.

Based on field observations and thermodynamic model simulation, the annual trend of PM2.5 acidity and its characteristics on non-hazy and hazy days in fall-winter of 2007-2012 in the Pearl River Delta region were investigated. Total acidity ([H(+)](total)) and in-situ acidity ([H(+)](in-situ)) of PM2.5 significantly decreased (F-test, p < 0.05) at a rate of -32 ± 1.5 nmol m(-3)year(-1) and -9 ± 1.7 nmol m(-3) year(-1), respectively. The variation of acidity was mainly caused by the change of the PM2.5 component, i.e., the decreasing rates of [H(+)](total) and [H(+)](in-situ) due to the decrease of sulfate (SO4(2-)) exceeded the increasing rate caused by the growth of nitrate (NO3(-)). [H(+)](total), [H(+)](in-situ) and liquid water content on hazy days were 0.9-2.2, 1.2-3.5 and 2.0-3.0 times those on non-hazy days, respectively. On hazy days, the concentration of organic matter (OM) showed significant enhancement when [H(+)](in-situ) increased (t-test, p < 0.05), while this was not observed on non-hazy days. Moreover, when the acidity was low (i.e., R = [NH4(+)]/(2 × [SO4(2-)]+[NO3(-)])>0.6), NH4NO3 was most likely formed via homogenous reaction. When the acidity was high (R ≤ 0.6), the gas-phase formation of NH4NO3 was inhibited, and the proportion of NO3(-) produced via heterogeneous reaction of N2O5 became significant.

Trends of ambient fine particles and major chemical components in the Pearl River Delta region: observation at a regional background site in fall and winter.

In the fall and winter of 2007 to 2011, 167 24-h quartz filter-based fine particle (PM2.5) samples were collected at a regional background site in the central Pearl River Delta. The PM2.5 showed an annual reduction trend with a rate of 8.58 µg m(-3) (p<0.01). The OC component of the PM2.5 reduced by 1.10 µg m(-3) yr(-1) (p<0.01), while the reduction rates of sulfur dioxide (SO2) and sulfate (SO4(2-)) were 10.2 µg m(-3) yr(-1) (p<0.01) and 1.72 µg m(-3) yr(-1) (p<0.01), respectively. In contrast, nitrogen oxides (NOx) and nitrate (NO(3-)) presented growth trends with rates of 6.73 µg m(-3) yr(-1) (p<0.05) and 0.79 µg m(-3) yr(-1) (p<0.05), respectively. The PM2.5 reduction was mainly related to the decrease of primary OC and SO4(2-), and the enhanced conversion efficiency of SO2 to SO4(2-) was related to an increase in the atmospheric oxidizing capacity and a decrease in aerosol acidity. The discrepancy between the annual trends of NOx and NO3(-) was attributable to the small proportion of NO3(-) in the total nitrogen budget. CAPSULE ABSTRACT: Understanding annual variations of PM2.5 and its chemical composition is crucial in enabling policymakers to formulate and implement control strategies on particulate pollution.

Source attributions of hazardous aromatic hydrocarbons in urban, suburban and rural areas in the Pearl River Delta (PRD) region.

Aromatic hydrocarbons (AHs) are both hazardous air pollutants and important precursors to ozone and secondary organic aerosols. Here we investigated 14 C6-C9 AHs at one urban, one suburban and two rural sites in the Pearl River Delta region during November-December 2009. The ratios of individual aromatics to acetylene were compared among these contrasting sites to indicate their difference in source contributions from solvent use and vehicle emissions. Ratios of toluene to benzene (T/B) in urban (1.8) and suburban (1.6) were near that of vehicle emissions. Higher T/B of 2.5 at the rural site downwind the industry zones reflected substantial contribution of solvent use while T/B of 0.8 at the upwind rural site reflected the impact of biomass burning. Source apportionment by positive matrix factorization (PMF) revealed that solvent use, vehicle exhaust and biomass burning altogether accounted for 89-94% of observed AHs. Vehicle exhaust was the major source for benzene with a share of 43-70% and biomass burning in particular contributed 30% to benzene in the upwind rural site; toluene, C8-aromatics and C9-aromatics, however, were mainly from solvent use, with contribution percentages of 47-59%, 52-59% and 41-64%, respectively.