Several factors can cause your Laser Egg's readings to be different from your local station's readings, but this is usually due to location and differences in the way air quality is reported. Your Laser Egg readings reflect the air quality in real-time whereas an air quality station is likely to update hourly.
Moreover, air quality can vary greatly over short distances, even in the same town or city. Your Laser Egg’s real-time readings reflect activities that are occurring in your immediate environment, such as cooking and using the fireplace, whereas the station is not being exposed to your hyper-local environment.
Similarly, other polluting factors could be occurring near your station that may cause differences between the readings on your Laser Egg and the station.