Levels of NO₂  found at the Sudbury Air Quality monitoring station downtown suggest that there problems at Vale may have begun a lot sooner than 6am this morning.

Those number began climbing from 2 parts per billion (ppb) around 8:00pm last night and by around 9pm had reach 13ppb, remaining between 12-14 until around 9am this morning with two noticeable spikes and 2am (20pbb) and again 8:00am (16ppb) this morning. Screen shots included below. You can also view them on the Ministry of Environment website.

Jody Kuzenko, Vale's general manager of production services for Sudbury, told the media at a press conference this afternoon that operations in Copper Cliff are in a planned maintenance which included routine washing of the sulfuric acid reservoirs.

This procedure normally creates a small amount of gas Kuzenko explained. But for reasons the company cannot yet explain, the gas was in a higher concentration than normal, and eventually traveled beyond Vale's property.

When the gas cloud travelled beyond their property at 6am, Vale sounded the alarm and issued an alert.

Kuzenko said the highest reading at the perimeter of Vale's property 0.5ppm (500ppb) and up to 3ppm over an 8 hour period is considered safe by the Ministry of Environment.

When questioned about the numbers reported by the Ministry's reporting station, Kate Jordan, a spokesperson with the Ontario Ministry of the Environment, said that the levels at the monitoring station don't reflect concentrations near the acid plant in Copper Cliff. Their data shows levels peaked at 6:37 a.m. at around 25 ppb.

When asked if the reading by the Ministry station suggest that problem started last night, Jordan stated that it will be one of the questions they'll be looking to answer as their investigation proceeds.

We emailed Vale asking if they could provide any explanation for the elevated levels beginning at 8pm and were told "The timeline on 8 pm is inconsistent with our incident and what we know as facts so far".