Fig. 4

The panels display the estimated partial effect for month and year, based on the inverse Gaussian generalized additive model: \( \begin{array}{l} \log \left({\mu}_t\right)={\alpha}_0+ \log \left({n}_t\right)+{f}_1\left({\mathrm{PM}}_{2.5, lag01}\right)I\left({\mathrm{flu}\ \mathrm{season}}_{\mathrm{t}}\right)+{f}_2\left({\mathrm{PM}}_{2.5, lag01}\right)I\left({\mathrm{nonflu}\ \mathrm{season}}_t\right)\\ {} + {f}_3\left({\mathrm{t}\mathrm{emperature}}_{\mathrm{t}}\right)+{f}_4\left({\mathrm{humidity}}_{\mathrm{t}}\right)+{f}_5\left({\mathrm{month}}_{\mathrm{t}}\right)+{\displaystyle {\sum}_k{\beta}_kI\left({\mathrm{year}}_{\mathrm{t}}=k\right).}\end{array} \) The solid lines indicate the estimated log relative risk of ILI and the dashed lines indicate the corresponding 95 % confidence intervals. For the effect of year, year 2008 is set as baseline