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Influence of isoprene chemical mechanism on modelled changes in tropospheric ozone due to climate and land use over the 21st century

机译：异戊二烯化学机理对21世纪气候和土地利用引起的对流层臭氧模拟变化的影响

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Isoprene is a~precursor to tropospheric ozone, a key pollutant and greenhousegas. Anthropogenic activity over the coming century is likely to cause largechanges in atmospheric CO levels, climate and land use, all of which willalter the global vegetation distribution leading to changes in isopreneemissions. Previous studies have used global chemistry–climate models toassess how possible changes in climate and land use could affect isopreneemissions and hence tropospheric ozone. The chemistry of isoprene oxidation,which can alter the concentration of ozone, is highly complex, therefore itmust be parameterised in these models. In this work, we compare the effect offour different reduced isoprene chemical mechanisms, all currently used inEarth system models, on tropospheric ozone. Using a box model we compareozone in these reduced schemes to that in a more explicit scheme (the Master Chemical Mechanism)over a range of NO and isoprene emissions, through the use of Oisopleths. We find that there is some variability, especially at highisoprene emissions, caused by differences in isoprene-derived NOreservoir species. A global model is then used to examine how the differentreduced schemes respond to potential future changes in climate, isopreneemissions, anthropogenic emissions and land use change. We find that,particularly in isoprene-rich regions, the response of the schemes variesconsiderably. The wide-ranging response is due to differences in the modeldescriptions of the peroxy radical chemistry, particularly their relativerates of reaction towards NO, leading to ozone formation, or HO, leadingto termination. Also important is the yield of isoprene nitrates andperoxyacyl nitrate precursors from isoprene oxidation. Those schemes thatproduce less of these NO reservoir species, tend to produce more ozonelocally and less away from the source region. We also note changes in otherkey oxidants such as NO and OH (due to the inclusion of additionalisoprene-derived HO recycling pathways). These have implications for secondary organic aerosolformation, as does the inclusion of an epoxide formation pathway in one ofthe mechanisms. By combining the emissions and O data from all of theglobal model integrations, we are able to construct isopleth plots comparableto those from the box model analysis. We find that the global and box modelisopleths show good qualitative agreement, suggesting that comparing chemicalmechanisms with a box model in this framework is a useful tool for assessingmechanistic performance in complex global models. We conclude that as thechoice of reduced isoprene mechanism may alter both the magnitude and sign ofthe ozone response, how isoprene chemistry is parameterised in perturbationexperiments such as these is a crucially important consideration. Moremeasurements and laboratory studies are needed to validate these reducedmechanisms especially under high-volatile-organic-compound, low-NO conditions.
机译：异戊二烯是对流层臭氧，关键污染物和温室气体的前体。未来一个世纪的人为活动可能会导致大气中CO水平，气候和土地利用的巨大变化，所有这些都会改变全球植被分布，导致等速变化。先前的研究已经使用了全球化学-气候模型来评估气候和土地利用的可能变化如何影响同量降水和对流层臭氧。可以改变臭氧浓度的异戊二烯氧化的化学过程非常复杂，因此必须在这些模型中进行参数设置。在这项工作中，我们比较了目前在地球系统模型中使用的四种不同的还原异戊二烯化学机制对对流层臭氧的影响。使用盒模型，我们通过使用Oisopleths将这些还原方案中的臭氧与更明确方案（主化学机理）中的NO和异戊二烯排放量进行比较。我们发现，由于异戊二烯衍生的NO储层物种的差异，存在一些变化，尤其是在异戊二烯排放高的情况下。然后，使用一个全球模型来研究不同的减排方案如何应对未来潜在的气候变化，同量降水，人为排放和土地利用变化。我们发现，特别是在富含异戊二烯的地区，该方案的响应差异很大。广泛的响应归因于过氧自由基化学模型描述的差异，特别是它们对NO的相对反应速率（导致臭氧形成或HO）导致终止。同样重要的是异戊二烯氧化的硝酸异戊二烯和硝酸过氧酰基硝酸酯前体的产率。那些产生这些NO储层物种较少的方案，倾向于在本地产生更多的臭氧，而远离源区的产生更少。我们还注意到其他关键氧化剂（例如NO和OH）的变化（由于包含了其他异戊二烯衍生的HO循环途径）。这些对二次有机气溶胶形成具有影响，在其中一种机理中包括环氧化物形成途径也具有意义。通过合并所有全局模型集成的排放和O数据，我们能够构建与箱模型分析可比的等值线图。我们发现全局模型和盒模型等价物显示出良好的定性一致性，表明在此框架下将化学机理与盒模型进行比较是评估复杂全局模型中机械性能的有用工具。我们得出结论，由于减少异戊二烯机理的选择可能会改变臭氧响应的幅度和迹象，因此如何在诸如此类的摄动实验中对异戊二烯化学进行参数化是至关重要的考虑因素。需要更多的测量和实验室研究来验证这些降低的机理，尤其是在高挥发性有机化合物，低NO条件下。

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