An intercomparison of weather normalization of PM2.5 concentration using traditional statistical methods, machine learning, and chemistry transport models
Huang Zheng, Shaofei Kong, Shixian Zhai, Xiaoyun Sun, Yi Cheng, Liquan Yao, Congbo Song, Zhonghua Zheng, Zongbo Shi, Roy M. Harrison
Abstract
Abstract Traditional statistical methods (TSM) and machine learning (ML) methods have been widely used to separate the effects of emissions and meteorology on air pollutant concentrations, while their performance compared to the chemistry transport model has been less fully investigated. Using the Community Multiscale Air Quality Model (CMAQ) as a reference, a series of experiments was conducted to comprehensively investigate the performance of TSM (e.g., multiple linear regression and Kolmogorov–Zurbenko filter) and ML (e.g., random forest and extreme gradient boosting) approaches in quantifying the effects of emissions and meteorology on the trends of fine particulate matter (PM 2.5 ) during 2013−2017. Model performance evaluation metrics suggested that the TSM and ML methods can explain the variations of PM 2.5 with the highest performance from ML. The trends of PM 2.5 showed insignificant differences ( p > 0.05) for both the emission-related ( $${{\rm{PM}}}_{2.5}^{{\rm{EMI}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>PM</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>EMI</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ) and meteorology-related components between TSM, ML, and CMAQ modeling results. $${{\rm{PM}}}_{2.5}^{{\rm{EMI}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>PM</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mi>EMI</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> estimated from ML showed the least difference to that from CMAQ. Considering the medium computing resources and low model biases, the ML method is recommended for weather normalization of PM 2.5 . Sensitivity analysis further suggested that the ML model with optimized hyperparameters and the exclusion of temporal variables in weather normalization can further produce reasonable results in emission-related trends of PM 2.5 .