Atmospheric Observation-based Evaluation of Fossil Fuel CO2 Emissions in London

政府、公司和个人正在采取行动减少温室气体排放和气候变化。在英国，官方政策正在根据2008年气候变化法案和2021年净零战略制定。到目前为止，造成气候变化的最大因素是化石燃料的燃烧，它向大气中排放二氧化碳。化石燃料二氧化碳排放量的量化方法是计算排放二氧化碳的活动，并乘以每个活动产生的二氧化碳量。然而，这些排放清单可能包含一些错误，如果没有独立检查的方法，就很难知道这些错误。通过在这个项目中测量大气中的二氧化碳，我们将采用新技术来检查伦敦的清单所计算的排放量。实际上，仅仅测量二氧化碳的浓度是不够的，因为二氧化碳也会受到光合作用和呼吸作用的影响，所以我们需要做其他的测量来告诉我们化石燃料的影响是什么。我们测量放射性碳（14C）的量，因为化石燃料太老了，它们的14C已经在放射性衰变中全部丢失了。因此，通过测量碳中碳含量的减少，我们可以量化一个地区增加的化石燃料二氧化碳。为了与排放清单进行比较，我们使用大气中的风模型来模拟化石燃料二氧化碳的预期量，看看是否与我们的观察结果相符。2020年，我们在伦敦对二氧化碳中的14C进行了初步测量，我们惊讶地发现，根据库存和模型模拟，化石燃料中的二氧化碳比预期的要多得多。由于当时只进行了几次测量，我们需要在伦敦周围进行更多的测量，看看是否发现了同样的差异。如果是这样，它表明定期测量伦敦二氧化碳中的14C将使我们能够独立估计化石燃料的二氧化碳排放量，并改进清单中的计算。我们通过初步数据观察到的另一件事是，根据英国的光合作用和呼吸作用模型，植被和土壤吸收的二氧化碳比预期的要多。该模型利用卫星对植物活动的观测，其分辨率非常高，可以看到城市中的植物。如果在这个项目中收集到更多的数据后，这一观察结果也成立，这可能表明伦敦在吸收额外的二氧化碳方面比我们想象的做得更多。该项目将使用最先进的大气测量和建模技术来评估伦敦的化石燃料二氧化碳排放量。研究结果将使我们对人类是如何导致气候变化的有一个重要的新认识，并帮助我们制定更好的计划来减少这些贡献。我们将通过与媒体合作和外联活动，与政府和公众分享项目成果。

Governments, companies and private citizens are taking actions to reduce greenhouse gas emissions and climate change. In the UK, official policies are being developed following the 2008 Climate Change Act and the 2021 Net Zero Strategy. The largest contributor to climate change by far is the burning of fossil fuels, which emits carbon dioxide (CO2) to the atmosphere. The way that fossil fuel CO2 emissions are quantified is by counting up the activities that emit CO2 and multiplying that by how much CO2 each activity produces. However, these emissions inventories can include errors that are difficult to know about without a way of checking them independently.By measuring CO2 in the atmosphere in this project, we will deploy new techniques to check the emissions calculated by the inventory in London. Actually it is not enough to measure the concentration of CO2 because CO2 is also affected by photosynthesis and respiration, so we need to make other measurements that tell us what the effect of fossil fuels is. We measure the amount of radiocarbon (14C) because fossil fuels are so old they have lost all their 14C to radioactive decay. Therefore, by measuring decreases in the fraction of carbon that is 14C, we can quantify the fossil fuel CO2 that has been added in a region. To compare with the emissions inventory, we use a model of the winds in the atmosphere to simulate the expected amount of fossil fuel CO2 and see if that matches our observations.In 2020, we made some preliminary measurements of 14C in CO2 in London and we were surprised to find there was much more fossil fuel CO2 than expected based on the inventories and model simulations. Since there were only a few measurements made then, we need to make more measurements around London and see if the same discrepancy is found. If so, it suggests that regularly measuring 14C in CO2 in London would allow us to estimate fossil fuel CO2 emissions independently, and to improve the calculations in the inventory.Another thing we observed with our preliminary data was that the effect of vegetation and soils was to take up more CO2 than expected, based on a model of photosynthesis and respiration in the UK. This model uses observations of plant activity from satellites with very high resolution that can see plants in cities. If this observation also holds when more data is collected in this project, it could suggest that London is doing more to absorb extra CO2 than we thought.This project will use state-of-the-art techniques for atmospheric measurement and modelling to evaluate fossil fuel CO2 emissions in London. The outcomes will provide a critical new understanding of how we are contributing to climate change and help us to make better plans to reduce these contributions. We will share the project outcomes with government and the public by working with the media and through outreach activities.