| 基于随机森林的北京城区臭氧敏感性分析 |
| 摘要点击 3300 全文点击 115 投稿时间：2023-06-05 修订日期：2023-08-04 |
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| 中文关键词 北京 臭氧（O3） O3-VOCs-NOx敏感性 随机森林（RF） SHAP值 |
| 英文关键词 Beijing ozone（O3） O3-VOCs-NOx sensitivity random forest （RF） SHAP value |
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| 中文摘要 |
| 明确臭氧（O3）与前体物的非线性关系是O3防控措施制定的基础和关键.基于北京城区站点2020年4~9月O3、挥发性有机物（VOCs）、氮氧化物（NOx）和气象要素在线观测,分析了O3及其前体物污染特征,利用随机森林（RF）模型结合SHAP值探究了影响O3的关键因素,并通过多情景分析探讨了O3-VOCs-NOx敏感性.相关性分析结果显示O3小时浓度与温度（T）呈显著正相关,与TVOCs和NOx呈显著负相关；但从每日结果来看,O3与T、TVOCs和NOx均呈显著正相关.RF模型模拟的O3浓度与实测值吻合较好,进一步计算了各个特征变量的SHAP值,结果显示T和NOx对O3影响最高,但前者是正向影响,而后者是负向影响.以观测期间O3污染天的NOx和VOCs平均值为基础情景,设置了对应不同NOx和VOCs的多种情景,并利用RF模型计算不同情景下的O3,得到O3等值线（EKMA曲线）,结果显示北京城区O3-VOCs-NOx敏感性处于VOCs控制区,与基于观测的盒子模型（OBM）得到的结果一致,这说明RF模型可以用作O3-VOCs-NOx敏感性分析的一种补充方法. |
| 英文摘要 |
| The basis and key step to developing ozone (O3) prevention and control measures is determining the non-linear relationship between O3 and its precursors. Based on online observations of O3, volatile organic compounds (VOCs), nitrogen oxides (NOx), and meteorological elements from April to September 2020 at an urban site in Beijing, we analyzed the pollution characteristics of O3 and its precursors, explored key factors affecting O3 using the random forest (RF) model combined with SHAP values, and explored the O3-VOCs-NOx sensitivity through a multi-scenarios analysis. The results of correlation analysis showed that the hourly concentration of O3 was significantly positively correlated with temperature (T) and negatively correlated with TVOCs and NOx. However, in terms of the daily values, O3 was significantly positively correlated with T, TVOCs, and NOx. The simulated O3 values by the RF model agreed with the measured values. The SHAP values of each characteristic variable were further calculated. The results suggested that T and NOx showed the two highest effects on O3, with positive and negative values, respectively. Based on the average NOx and VOCs on O3 pollution days during the observation period (the base scenario), multi-scenarios with different NOx and VOCs were set up. The RF model was used to calculateO3 under different scenarios and obtain the O3 isopleth (EKMA curve). The results showed that the O3-VOCs-NOx sensitivity in urban areas of Beijing was in the VOCs-limited regime, which was consistent with the results obtained from the observation-based box model(OBM). This indicated that the RF model could be used as a complementary method for O3-VOCs-NOx sensitivity analysis. |
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