Delhi, India, has had the highest fine particle mass (PM_2.5; diameter < 2.5 µm) concentrations of any megacity on the planet in recent years. Here, we undertook a year of detailed measurements of particle size distributions. We observed that the number count of ultrafine particles (diameter < 100 nm) – unlike PM_2.5 – is not dramatically elevated in Delhi. Using observations and a simple model, we illustrate how the high amount of PM_2.5 in Delhi may suppress ultrafine particle concentrations.