Shaodong Xie

Secondary nitrate is a major driver of wintertime PM2.5 pollution in China, yet the coupled photochemical and heterogeneous controls on its formation remain poorly constrained in humid, topographically confined basins. Here, we combined wintertime field observations with a box model and thermodynamic calculations to quantify nitrate formation pathways, radical chemistry, and precursor sensitivities. During pollution episodes, nitrate became the dominant PM2.5 component, systematically co-varied with elevated NO2, Ox, and aerosol liquid water content (ALWC). Pathway-resolved modeling revealed near-equal contributions from the two dominant nitrate formation pathways, daytime OH+NO2 reactions (52%) and nighttime heterogeneous N2O5 hydrolysis (46%), with the latter increasing sharply during polluted episodes. The modeled OH budget indicated efficient HOx recycling, dominated by HO2+NO recycling. Binning regressions identified critical thresholds of RH = 87% and ALWC = 76.5 μg m–3, above which nitrate formation efficiency increased abruptly. Sensitivity analyses indicated that VOCs exerted a slightly stronger control on nitrate formation than NOx, with oxygenated VOCs and alkenes as the most influential groups, and solvent usage and vehicle exhaust as dominant sources. These results reveal a humidity-modulated dual-pathway mechanism for wintertime nitrate formation sustained by VOC-influenced radical cycling. Effective nitrate mitigation therefore requires coordinated reductions in NOx and reactive VOCs, together with measures that limit aerosol water accumulation under high-humidity conditions.

Despite growing concern, there is limited comprehensive and up-to-date research on the burden, disparities, and inequalities of depressive disorders in the Western Pacific region. We obtained data from the Global Burden of Disease Study (GBD; 2021) for the Western Pacific region. We reported the prevalence and disability-adjusted life years (DALYs) rates of depressive disorders from 1990 to 2021. Our results showed that the prevalence of depressive disorders in the Western Pacific region was 1723.1 per 100,000 people (95% UI: 1359.2–2164.9), contributing to 1057.3 DALYs per 100,000 (95% UI: 683.0–1551.8). From 1990 to 2021, the burden of depressive disorders initially decreased but then increased, with Japan, Malaysia, and South Korea seeing the most significant rise. The burden grew with age, especially in the 10–14 age group, and exhibited significant sex disparities, especially in this age group. Among 31 countries, those with higher UHC scored had higher prevalence rates, but the gap between high- and low-UHC countries has decreased over time, indicating that countries with lower UHC might face greater challenges in the future. Our results highlight the differences in burden by sex and age call for targeted policies and interventions to promote youth mental health. Accelerating universal health coverage could be a key strategy to further reduce this high burden.

The emissions and secondary transformations of volatile organic compounds (VOCs) play a significant role in ozone (O₃) formation. Previous studies have often relied on ambient VOC concentrations to identify key species. However, ambient concentrations represent the residual concentrations after the emitted VOCs have been consumed, which can introduce substantial uncertainties. To address this issue, this study proposes a novel method to identify the key VOC species in both anthropogenic and biogenic emissions. The emitted VOC concentrations are calculated during both nighttime and daytime in summer using the nitrate radical, O₃, and hydroxyl radical reaction rates and ambient concentrations of 99 VOCs measured at Deyang, Chengdu, and Meishan, China. The emitted concentrations of alkenes and aromatics are higher than the ambient concentrations. The largest differences between emitted and ambient concentrations are 1.04 ppbv for cis-2-butene at Deyang, 0.81 ppbv for isoprene at Chengdu, and 1.79 ppbv for isoprene at Meishan. In contrast, due to secondary production, the emitted concentrations of oxygenated VOCs are lower than the ambient concentrations. The largest differences are −0.54 ppbv for acetone at Deyang, −0.58 ppbv for acetaldehyde at Chengdu, and −0.5 ppbv for acetone at Meishan. Based on the emitted concentrations, isoprene is one of the top three species contributing to O₃ formation at all three sites, which may be overlooked in observed concentrations. Comprehensive calculation of the emitted VOC concentrations enables the key VOC species in O₃ formation to be accurately identified.

To reduce the uncertainties in identifying key volatile organic compounds (VOCs) species influencing ozone (O₃) formation based on observed VOCs concentrations, this study proposed key species identification from the initial VOCs concentrations. The initial VOCs concentrations during the daytime and nighttime were calculated using reaction rates and hourly measured 99 VOCs concentrations at Deyang, Chengdu, and Meishan, southwest China during summer. The initial concentrations of alkenes and aromatics were higher than the measured ones. The largest differences between initial and measured concentrations were 1.04 ppbv for cis-2-butene at Deyang, 0.86 ppbv for isoprene at Chengdu, and 1.98 ppbv for isoprene at Meishan, respectively. Due to secondary production, the initial concentrations of oxygenated VOCs were lower than the measured ones. The largest differences were -0.54 ppbv for acetone at Deyang, -0.58 ppbv for acetaldehyde at Chengdu, and -0.5 ppbv for acetone at Meishan, respectively. Based on the initial concentrations, the top three species contributing to O₃ formation potential were cis-2-butene, isoprene, m,p-xylene at Deyang; m,p-xylene, isoprene, acetaldehyde at Chengdu; and isoprene, ethylene, acetaldehyde at Meishan, respectively. These results differed from those based on observed concentrations. Comprehensively calculating the initial concentrations of VOCs helps accurately identify the key VOC species influencing O₃ formation.

To reduce the uncertainties in identifying key volatile organic compounds (VOCs) species influencing ozone (O₃) formation based on observed VOCs concentrations, this study proposed key species identification from the initial VOCs concentrations. The initial VOCs concentrations during the daytime and nighttime were calculated using reaction rates and hourly measured 99 VOCs concentrations at Deyang, Chengdu, and Meishan, southwest China during summer. The initial concentrations of alkenes and aromatics were higher than the measured ones. The largest differences between initial and measured concentrations were 1.04 ppbv for cis-2-butene at Deyang, 0.86 ppbv for isoprene at Chengdu, and 1.98 ppbv for isoprene at Meishan, respectively. Due to secondary production, the initial concentrations of oxygenated VOCs were lower than the measured ones. The largest differences were -0.54 ppbv for acetone at Deyang, -0.58 ppbv for acetaldehyde at Chengdu, and -0.5 ppbv for acetone at Meishan, respectively. Based on the initial concentrations, the top three species contributing to O₃ formation potential were cis-2-butene, isoprene, m,p-xylene at Deyang; m,p-xylene, isoprene, acetaldehyde at Chengdu; and isoprene, ethylene, acetaldehyde at Meishan, respectively. These results differed from those based on observed concentrations. Comprehensively calculating the initial concentrations of VOCs helps accurately identify the key VOC species influencing O₃ formation.

To reduce the uncertainties in identifying key volatile organic compounds (VOCs) species influencing ozone (O₃) formation based on observed VOCs concentrations, this study proposed key species identification from the initial VOCs concentrations. The initial VOCs concentrations during the daytime and nighttime were calculated using reaction rates and hourly measured 99 VOCs concentrations at Deyang, Chengdu, and Meishan, southwest China during summer. The initial concentrations of alkenes and aromatics were higher than the measured ones. The largest differences between initial and measured concentrations were 1.04 ppbv for cis-2-butene at Deyang, 0.86 ppbv for isoprene at Chengdu, and 1.98 ppbv for isoprene at Meishan, respectively. Due to secondary production, the initial concentrations of oxygenated VOCs were lower than the measured ones. The largest differences were -0.54 ppbv for acetone at Deyang, -0.58 ppbv for acetaldehyde at Chengdu, and -0.5 ppbv for acetone at Meishan, respectively. Based on the initial concentrations, the top three species contributing to O₃ formation potential were cis-2-butene, isoprene, m,p-xylene at Deyang; m,p-xylene, isoprene, acetaldehyde at Chengdu; and isoprene, ethylene, acetaldehyde at Meishan, respectively. These results differed from those based on observed concentrations. Comprehensively calculating the initial concentrations of VOCs helps accurately identify the key VOC species influencing O₃ formation.

To reduce the uncertainties in identifying key volatile organic compounds (VOCs) species influencing ozone (O₃) formation based on observed VOCs concentrations, this study proposed key species identification from the initial VOCs concentrations. The initial VOCs concentrations during the daytime and nighttime were calculated using reaction rates and hourly measured 99 VOCs concentrations at Deyang, Chengdu, and Meishan, southwest China during summer. The initial concentrations of alkenes and aromatics were higher than the measured ones. The largest differences between initial and measured concentrations were 1.04 ppbv for cis-2-butene at Deyang, 0.86 ppbv for isoprene at Chengdu, and 1.98 ppbv for isoprene at Meishan, respectively. Due to secondary production, the initial concentrations of oxygenated VOCs were lower than the measured ones. The largest differences were -0.54 ppbv for acetone at Deyang, -0.58 ppbv for acetaldehyde at Chengdu, and -0.5 ppbv for acetone at Meishan, respectively. Based on the initial concentrations, the top three species contributing to O₃ formation potential were cis-2-butene, isoprene, m,p-xylene at Deyang; m,p-xylene, isoprene, acetaldehyde at Chengdu; and isoprene, ethylene, acetaldehyde at Meishan, respectively. These results differed from those based on observed concentrations. Comprehensively calculating the initial concentrations of VOCs helps accurately identify the key VOC species influencing O₃ formation.