Introduction While secondhand smoke exposure in outdoor spaces has been investigated before, no data on outdoor secondhand smoke exposure have been collected in the Netherlands. Such data could help policymakers gain support for smoke-free outdoor public spaces. Methods Between May and November 2021, we visited 25 outdoor locations across the Netherlands. At each location, we conducted four measurements with smokers and one measurement without smokers. During each measurement, we counted the number of smokers present and we rated tobacco smell intensity on a fivepoint scale. Airborne nicotine and 3-ethenylpyridine (3-EP) data were collected through active sampling on thermal desorption tubes. The contents of these tubes were later analyzed using gas chromatography-mass spectrometry. Using linear mixed models, we investigated the association between levels of nicotine and the presence of smokers, the number of smokers, and the intensity of tobacco smell. We also investigated these association with levels of 3-EP. Results Nicotine levels were higher when smokers were present (B=1.40; 95% CI: 0.69– 2.11, p<0.001). For each additional smoker present, we measured higher levels of nicotine (B=0.23; 95% CI: 0.10–0.37, p=0.001). When the smell of tobacco smoke was noted to be stronger by the researchers, higher levels of nicotine were measured through sampling (B=0.85; 95% CI: 0.44–1.26, p<0.001). We found similar results for 3-EP levels. Conclusions This study showed that both nicotine and 3-EP are useful in quantifying levels of secondhand smoke in various outdoor locations. The level of nicotine exposure outdoors was positively associated with the number of smokers nearby. The intensity of the tobacco smell was also related to nicotine exposure: the stronger the smell of tobacco smoke, the more nicotine was measured in the air.