Figure 1.

(a) Morning, midday, and evening measurements of atmospheric NO_x concentrations, recorded daily around 9.00, 12.30, and 18.00. Each data point is the average of the measured NO_x concentration over 5 min. (b) NO_x removal efficiency over time, measured for an inlet gas mixture of 50 ppm of NO in He at 10 mL min^–1 for different scrubbers and liquid traps. S1 and S2 indicate two standard scrubbers connected in series and the in-house-made scrubber, respectively. (c) NO concentrations measured over time at the outlet of each gas filter with an inlet gas mixture of 50 ppm of NO in He at 50 (dashed line) and 10 (solid line) mL min^–1. The in-house-made scrubber (S2) is filled with a 0.1 M KOH and 0.1 M NaClO₂ trapping solution. The complete data set with flow rates from 1 to 50 mL min^–1 is given in Figure S8.