AE-16 Aethalometer data taken under clean air conditions, illustrating sensitivity and noise

These charts show measurements taken with the Model AE-16 Aethalometer under clean air conditions in Berkeley, California, approximately directly opposite the Golden Gate Bridge and the Pacific Ocean. Strong onshore winds can bring extremely clean maritime air across the San Francisco Bay to our location with only a slight addition of combustion-derived exhaust during rapid passage over the city of Berkeley. Under these conditions, the aethalometer readings can be in the low tens of nanograms per cubic meter, and this is a good test of the instrument's stability and sensitivity.

These charts show two days of unedited data recorded on a 5-minute timebase. In the early morning hours of Monday April 26, particulate elemental carbon concentrations were on the order of 30 to 50 ng/m3. The wind subsided a little in the mid-morning, allowing concentrations to rise to around 1500 ng/m3, but then the wind picked up speed again and concentrations decreased. On Tuesday April 27, moderate winds kept the BC concentrations low except for occasional 'spikes' due to nearby individual vehicles.

Note that the inherent instrumental noise is small compared to the measurement variability. The data taken early on Monday morning show the typical noise fluctuations of some tens of nanograms. The point-to-point variability shown later on that same day is due to fluctuations in the actual BC content of the air, not only instrumental noise.


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