Influence of photochemical loss of volatile organic compounds on understanding ozone formation mechanism

Volatile organic compounds (VOCs) tend to be consumed by atmospheric oxidants, resulting in substantial photochemical loss during transport. An observation-based model was used to evaluate the influence of photochemical loss of VOCs on the sensitivity regime and mechanisms of ozone formation. Our results showed that a VOC-limited regime based on observed VOC concentrations shifted to a transition regime with a photochemical initial concentration of VOCs (PIC-VOCs) in the morning. The net ozone formation rate was underestimated by 3 ppbh(-1) (similar to 36 ppb d(-1)) based on the measured VOCs when compared with the PIC-VOCs. The relative contribution of the RO2 path to ozone production based on the PIC-VOCs accordingly increased by 13.4 %; in particular, the contribution of alkene-derived RO(2 )increased by approximately 10.2 %. In addition, the OH-HO2 radical cycle was obviously accelerated by highly reactive alkenes after accounting for photochemical loss of VOCs. The contribution of local photochemistry might be underestimated for both local and regional ozone pollution if consumed VOCs are not accounted for, and policymaking on ozone pollution prevention should focus on VOCs with a high reactivity.Peer reviewe

Strong impacts of biomass burning, nitrogen fertilization, and fine particles on gas-phase hydrogen peroxide (H2O2)

Gas-phase hydrogen peroxide (H2O2) plays an important role in atmospheric chemistry as an indicator of the atmospheric oxidizing capacity. It is also a vital oxidant of sulfur dioxide (SO2) in the aqueous phase, resulting in the formation of acid precipitation and sulfate aerosol. However, sources of H2O2 are not fully understood especially in polluted areas affected by human activities. In this study, we reported some high H2O2 cases observed during one summer and two winter campaigns conducted at a polluted rural site in the North China Plain. Our results showed that agricultural fires led to high H(2)O(2 )concentrations up to 9 ppb, indicating biomass burning events contributed substantially to primary H2O2 emission. In addition, elevated H2O2 and O-3 concentrations were measured after fertilization as a consequence of the enhanced atmospheric oxidizing capacity by soil HONO emission. Furthermore, H2O2 exhibited unexpectedly high concentration under high NOx conditions in winter, which are closely related to multiphase reactions in particles involving organic chromophores. Our findings suggest that these special factors (biomass burning, fertilization, and ambient particles), which are not well considered in current models, are significant contributors to H2O2 production, thereby affecting the regional atmospheric oxidizing capacity and the global sulfate aerosol formatio

Does a higher cutoff value of lymph node retrieval substantially improve survival in patients with advanced gastric cancer? : time to embrace a new digit

Background. The present study assessed the impact of the retrieval of >25 lymph nodes (LNs) on the survival outcome of patients with advanced gastric cancer after curative‐intent gastrectomy. Patients and Methods. A total of 5,386 patients who had undergone curative gastrectomy for gastric cancer from 1994 to 2011 were enrolled. The clinicopathological parameters and overall survival (OS) were analyzed according to the number of LNs examined (≤15, n = 916; 16–25, n = 1,458; and >25, n = 3,012). Results. The percentage of patients with >25 LNs retrieved increased from 1994 to 2011. Patients in the LN >25 group were more likely to have undergone total gastrectomy and to have a larger tumor size, poorer tumor differentiation, and advanced T and N stages. Hospital mortality among the LN ≤15, LN 16–25, and LN >25 groups was 6.1%, 2.7%, and 1.7%, respectively (p 25 group consistently exhibited the most favorable OS, in particular, with stage II disease (p = .011) when OS was stratified according to tumor stage. Similarly, the LN >25 group had significantly better OS in all nodal stages (from N1 to N3b). The discrimination power of the lymph node ratio (LNR) for the LN ≤15, LN 16–25, and LN >25 groups was 483, 766, and 1,560, respectively. Multivariate analysis demonstrated that the LNR was the most important prognostic factor in the LN >25 group. Conclusion. Retrieving more than 25 lymph nodes during curative‐intent gastrectomy substantially improved survival and survival stratification of advanced gastric cancer without compromising patient safety

Atmospheric measurements at Mt. Tai – Part II: HONO budget and radical (ROx + NO3) chemistry in the lower boundary layer

International audienceAbstract. In the summer of 2018, a comprehensive field campaign, with measurements on HONO and related parameters, was conducted at the foot (150 m a.s.l.) and the summit of Mt. Tai (1534 m a.s.l.) in the central North China Plain (NCP). With the implementation of a 0-D box model, the HONO budget with six additional sources and its role in radical chemistry at the foot station were explored. We found that the model default source, NO + OH, could only reproduce 13 % of the observed HONO, leading to a strong unknown source strength of up to 3 ppbv h−1. Among the additional sources, the NO2 uptake on the ground surface dominated (∼ 70 %) nighttime HONO formation, and its photo-enhanced reaction dominated (∼ 80 %) daytime HONO formation. Their contributions were sensitive to the mixing layer height (MLH) used for the parameterizations, highlighting the importance of a reasonable MLH for exploring ground-level HONO formation in 0-D models and the necessity of gradient measurements. A ΔHONO/ΔNOx ratio of 0.7 % for direct emissions from vehicle exhaust was inferred, and a new method to quantify its contribution to the observations was proposed and discussed. Aerosol-derived sources, including the NO2 uptake on the aerosol surface and the particulate nitrate photolysis, did not lead to significant HONO formation, with their contributions lower than NO + OH. HONO photolysis in the early morning initialized the daytime photochemistry at the foot station. It was also a substantial radical source throughout the daytime, with contributions higher than O3 photolysis to OH initiation. Moreover, we found that OH dominated the atmospheric oxidizing capacity in the daytime, while modeled NO3 appeared to be significant at night. Peaks of modeled NO3 time series and average diurnal variation reached 22 and 9 pptv, respectively. NO3-induced reactions contribute 18 % of nitrate formation potential (P(HNO3)) and 11 % of the isoprene (C5H8) oxidation throughout the whole day. At night, NO3 chemistry led to 51 % and 44 % of P(HNO3) or the C5H8 oxidation, respectively, implying that NO3 chemistry could significantly affect nighttime secondary organic and inorganic aerosol formation in this high-O3 region. Considering the severe O3 pollution in the NCP and the very limited NO3 measurements, we suggest that besides direct measurements of HOx and primary HOx precursors (O3, HONO, alkenes, etc.), NO3 measurements should be conducted to understand the atmospheric oxidizing capacity and air pollution formation in this and similar regions

Atmospheric Hydrogen Peroxide (H 2 O 2 ) at the Foot and Summit of Mt. Tai: Variations, Sources and Sinks, and Implications for Ozone Formation Chemistry

International audienceHydrogen peroxide (H 2 O 2) acts as a terminal sink for atmospheric HO x radicals (OH and HO 2), playing a key role in tropospheric O 3 formation. However, there are few field measurements of atmospheric H 2 O 2 to assess its role in O 3 formation, especially for the seriously polluted region of the North China Plain. In this study, H 2 O 2 concentrations were measured at the foot of Mt. Tai from May to July 2018 and the summit of Mt. Tai from May to June 2019, with average values of 0.93 ± 1.01 and 2.05 ± 1.20 ppb, respectively. H 2 O 2 exhibited a pronounced diurnal variation with a noon-peak at the foot of Mt. Tai, which could be well reproduced by a gas-phase box model with H 2 O 2 dry deposition velocity of 3 cm s −1 included, indicating H 2 O 2 was mainly photochemically produced. Modeling analysis showed H 2 O 2 production at the foot was most sensitive to alkenes and aromatics, while the source and sink for H 2 O 2 were dominated by HO 2 recombination and dry deposition, respectively. Compared with the summer-measurement in 2007, the remarkable elevation of H 2 O 2 at the summit might be ascribed to volatile organic compounds (VOCs) increase and SO 2 decline. Both H 2 O 2-O 3 correlation and H 2 O 2 / NO z ratio suggested O 3 formation at the foot of Mt. Tai was mainly VOC-sensitive in the early morning and shifted to NO x-sensitive thereafter. Therefore, reduction of VOCs emission especially for the reactive species of alkenes and aromatics in the morning as well as NO x emission around noontime will be effective for mitigating the serious O 3 (as well as H 2 O 2) pollution in Tai'an city. YE ET AL