For well over a century, many advances in tropospheric chemistry and physics have been driven by in situ observations, with measurements tending to be either specific measurements over multi-year periods, often as part of a network, or short term ‘intensive’ observations over of a more limited duration, typically 1-2 months. But in recent decades, many major developments in atmospheric science have been fueled through long-term comprehensive observations, and the Finnish SMEAR project is a major pioneering example of this. As part of the 20th anniversary Special Issue of Atmospheric Chemistry and Physics, this opinion piece reflects on the manifold and sustained contributions this has made to atmospheric science.