Pollution monitors around the Mossmorran chemical plant in Fife have been failing, the environmental watchdog has admitted.
Figures from Sepa show at least one of its three monitoring sites was not working during 13 days in January.
There are air pollution monitors at Auchtertool, Donibristle and Lochgelly.
The plant is being restarted following a shutdown in August. Sepa said there were 10 full days when monitors in Auchtertool and Donibristle were down.
Sepa reports show faults with the monitors' analysers.
Remote connectivity has also failed to the monitors on several occasions since they were installed in October.
The reports said "a power fault at the Donibristle site means data is not available from Friday 8 November 2019" and "Both analysers run on mains power but the data logger attached to them runs on solar power and this has resulted in intermittent data".
The equipment has been installed to record air quality around the Mossmorran petrochemical plant following concerns from local residents over several unplanned flaring events.
Andy Adam, 55, who lives in Cowdenbeath near the plant told BBC Scotland: "I had a phone call with Ian Brocklebank and Richard Sinnott from Sepa where I asked them how they could report the air quality was fine around Mossmorran when their monitors have been failing up to fives days at a time.
"They said all three monitors haven't failed all at once. My concern is that if one is down it becomes a lottery as to the accuracy of the reporting because it depends which way the wind is blowing.
"When I suggested they install two monitors at each site as back up they said they couldn't because the monitors were too expensive.
"I told them also that in Sepa's written warning to Exxonmobil it had 'inadequate holding of spares', which should also apply to Sepa then too."
There were reports of huge flaring on Thursday night with residents making a flood of complaints to environment watchdog Sepa.
A spokeswoman for the Scottish Environment Protection Agency (Sepa) said: "Sepa is committed to both fully monitoring the restart of the Fife site with regulatory, noise and air monitoring capabilities across local communities whilst addressing the root causes of 'unacceptable flaring'.
"These are supported by a backup mobile air modelling unit located on a local farm to ensure a continuous flow of data.
"There have been 10 days since deployment where power issues on an individual unit has reset the unit.
"This is a control process to ensure no erroneous data is recorded.
"On each occasion there has been backup data from the ring of fixed and mobile monitors and there are no days where data as a whole has not been available."