The amount of particulate matter in the air of a certain region was increasing exponentially with time due to malfunctioning scrubbers in a factory's chimneys. It was concluded that the amount of particulate matter, in parts per million (ppm), could be modeled with the equation P(t)=ab^t, where a and b are constants and t is the time in hours. Three hours after the problem was first noticed, the particulate concentration was 54,000 ppm. Two hours later (t=5), the concentration had increased to 486,000 ppm. 

What was the approximate concentration, in ppm, when the problem was first noticed?