Wintertime ozone surges:The critical role of alkene ozonolysis

Ozone(O_(3))pollution is usually linked to warm weather and strong solar radiation,making it uncommon in cold winters.However,an unusual occurrence of four high O_(3)episode days(with maximum hourly concentrations exceeding 100 ppbv and peaking at 121 ppbv)was recorded in January 2018 in Lanzhou city,China.During these episodes,the average daytime concentration of total non-methane volatile organic compounds(TVOCs)reached 153.4±19.0 ppbv,with alkenes—largely emitted from the local petrochemical industry—comprising 82.3±13.1 ppbv.Here we show a photochemical box model coupled with a Master Chemical Mechanism to elucidate the mechanisms behind this unusual wintertime O_(3)pollution.We find that the typically low temperatures(−1.7±1.3℃)and weak solar radiation(263.6±60.7 W m^(-2))of those winter episode days had a minimal effect on the reactivity of VOCs with OH radicals.Instead,the ozonolysis of alkenes generated Criegee intermediates,which rapidly decomposed into substantial ROx radicals(OH,HO_(2),and RO_(2))without sunlight.This radical production led to the oxidation of VOCs,with alkene ozonolysis ultimately contributing to 89.6±8.7%of the O_(3)formation during these episodes.This mechanism did not activate at night due to the depletion of O_(3)by the NO titration effect.Furthermore,the findings indicate that a reduction of alkenes by 28.6%or NO_(x)by 27.7%in the early afternoon could significantly mitigate wintertime O_(3)pollution.Overall,this study unravels the unique mechanism of alkene-induced winter O_(3)pollution and offers a reference for winter O_(3)reduction strategies in the petrochemical industrial regions.

Large-scale land-sea interactions extend ozone pollution duration in coastal cities along northern China

Land-sea atmosphere interaction(LSAI)is one of the important processes affecting ozone(O_(3))pollution in coastal areas.The effects of small-scale LSAIs like sea-land breezes have been widely studied.However,it is not fully clear how and to what extent the large-scale LSAIs affect O_(3) pollution.Here we explored an O_(3) episode to illuminate the role of large-scale LSAIs in O_(3) pollution over the BohaieYellow Seas and adjacent areas through observations and model simulations.The results show that the northern Bohai Sea's coastal region,influenced by the Mongolian High,initially experienced a typical unimodal diurnal O_(3) variation for three days,when O_(3) precursors from BeijingeTianjineHebei,Shandong,and Northeast China were transported to the BohaieYellow Seas.Photochemical reactions generated O_(3) within marine air masses,causing higher O_(3) levels over the seas than coastal regions.As the Mongolian High shifted eastward and expanded,southerly winds on its western edge transported O_(3)-rich marine air masses toward the coast,prolonging pollution for an additional three days and weakening diurnal variations.Subsequently,emissions from the Korean Peninsula and marine shipping significantly affected O_(3) levels in the northern Bohai Sea(10.7%and 13.7%,respectively).Notably,Shandong's emissions played a substantial role in both phases(27.5%and 26.1%,respectively).These findings underscore the substantial impact of large-scale LSAIs driven by the Mongolian High on O_(3) formation and pollution duration in coastal cities.This insight helps understand and manage O_(3) pollution in northern Bohai Sea cities and broadly applies to temperate coastal cities worldwide.

Urban heat mitigation by green and blue infrastructure:Drivers,effectiveness,and future needs

The combination of urbanization and global warming leads to urban overheating and compounds the frequency and intensity of extreme heat events due to climate change.Yet,the risk of urban overheating can be mitigated by urban green-blue-grey infrastructure(GBGI),such as parks,wetlands,and engineered greening,which have the potential to effectively reduce summer air temperatures.Despite many reviews,the evidence bases on quantified GBGI cooling benefits remains partial and the practical recommendations for implementation are unclear.This systematic literature review synthesizes the evidence base for heat mitigation and related co-benefits,identifies knowledge gaps,and proposes recommendations for their implementation to maximize their benefits.After screening 27,486 papers,202 were reviewed,based on 51 GBGI types categorized under 10 main divisions.Certain GBGI(green walls,parks,street trees)have been well researched for their urban cooling capabilities.However,several other GBGI have received negligible(zoological garden,golf course,estuary)or minimal(private garden,allotment)attention.The most efficient air cooling was observed in botanical gardens(5.0±3.5℃),wetlands(4.9±3.2℃),green walls(4.1±4.2℃),street trees(3.8±3.1℃),and vegetated balconies(3.8±2.7℃).Under changing climate conditions(2070–2100)with consideration of RCP8.5,there is a shift in climate subtypes,either within the same climate zone(e.g.,Dfa to Dfb and Cfb to Cfa)or across other climate zones(e.g.,Dfb[continental warm-summer humid]to BSk[dry,cold semi-arid]and Cwa[temperate]to Am[tropical]).These shifts may result in lower efficiency for the current GBGI in the future.Given the importance of multiple services,it is crucial to balance their functionality,cooling performance,and other related co-benefits when planning for the future GBGI.This global GBGI heat mitigation inventory can assist policymakers and urban planners in prioritizing effective interventions to reduce the risk of urban overheating,filling research gaps,and promoting community resilience.