The
chemical compositions of atmospheric particles have been studied
for several decades, and the traditional techniques for particle analysis
usually require time-consuming sample preparation. Within this study,
simultaneous quantitative detection of multiple metallic species (Zn,
Cu, and Ni) in single micro-sized suspended particles was investigated
by combining random forest (RF) and variable selection strategies.
Laser-induced breakdown spectra of 15 polluted black carbon samples
were applied for establishing the RF model, and the movmean smoothing
spectral pretreatment method and variable selection methods [variable
importance measurement (VIM), genetic algorithm (GA), and variable
importance projection (VIP)] were proposed. Finally, the optimized
RF calibration model with the evaluation indicators of mean relative
error (MRE), root-mean-square error (RMSE), and coefficient of determination
(R
2) was constructed based on the optimal
input variables and model parameters. Compared with the univariate
regression method, the VIP-RF (Zn) and VIM-RF (Cu and Ni) models showed
a better correlation relationship (R
p
2 = 0.9662 for Zn, R
p
2 = 0.9596 for Cu, and R
p
2 =
0.9548 for Ni). For Zn, Cu, and Ni, the values of RMSEP (RMSE of prediction)
decreased by 116.44, 68.94, and 102.10 ppm, while the values of MREP
(MRE of prediction) decreased by 67, 55, and 48%, respectively. The
values of ratio of prediction to deviation (RPD) of VIP-RF (Zn), VIM-RF
(Cu), and VIM-RF (Ni) models were 5.4, 5.0, and 4.7, respectively.
The performance of this combined approach displays a notable accuracy
improvement in the quantitative analysis of single particles, suggesting
that it is a promising tool for real-time air particulate matter pollution
monitoring and control in the future.