Fig. 5: The linear or nonlinear regression curves between IAC and each environmental factors and their corresponding threshold values (i.e., PM10, PM2.5, SO2, CO, NO2, O3, Air pressure, Air temperature, Visibility, and Relative humidity) in Northeast China.

IAC incidence of allergic conjunctivitis, AP Air pressure, AT Air temperature, RH Relative humidity, V Visibility, PR Precipitation. The gray solid circle is the paired data for the IAC and each factor; the yellow solid circle is outliers that not used in regression analysis; the red hollow circle is the threshold for each factor