Last night between 11pm and midnight I noticed a strange smell coming into the house from the patio. It’s not the first time this has happened, usually at night. Once I was taking my dog out to the plaça for her last walk and we had to hurry home because the smell was so strong that I thought one of the nearby chemical factories had broken a leak. We rang the police to report it but heard no more. Yesterday it was strong but not quite so bad as on the other occasion. Strong enough to make us close the doors and windows though and even after only ten minutes of breathing it in I had a metallic taste at the back of my throat. In the early hours of the morning I woke up with the smell still wafting around my nose. I closed the bedroom door and windows and it stopped. For god’s sake! What is it? It is worrying. Granollers is in a valley with the river Congost running through, slowly making its way down to Barcelona and the sea. Along the river banks are many large factories, some of them petro-chemicals, and in the past the waters were polluted by industrial waste. Now there is more control and the river again has fish and bird life. People walk and run along the pathes on either side. Usually the air feels fine to breathe but we all know there is pollution you cannot see or feel. I don’t want to sound paranoid but it’s just this funny smell….it comes and it goes 
The smell is surely a sign of something going on – but I don’t know what. I have never heard anyone mention it nor seen discussions in the local paper about the need to monitor closely the surrounding factories. What I do know is that there is a chemical alert siren which is regularly tested and you are supposed to know the difference between a drill and the real thing. When it is real you are told to close and seal windows and doors and stay inside. A few months ago the siren started and as we hadn’t received any notices of a test we raced around closing things down. Then I looked outside and everyone was walking around as normal, ignoring the siren and not falling down dead on the street. So we also just got on with life. But how would we all know if it was serious? There is also the dark fine dust that coats all surfaces in our houses. Every day when I wipe around the bath the cloth picks up a black stain. I have been told that in the past Granollers was so full of factories that it still sits in a cloud of textile particles. Really? I think I will have to look into it. I want to know what the smell means? Where does it come from? Who is monitoring the levels of pollutants that are blowing around the town? And has that dust been analysed and pronounced harmless? If anyone knows more about this or has any suggestions about what I can do to get information then please do let me know. Anything I find out, I will let you know
about granollers 
I sympathise with you and understand your concern about the smell, I’ve had a similar experience myself. Not here in Spain but in rural North Yorkshire. We’d moved to a remote farmhouse out on the moor and every so often I’d smell this weird smell (a bit like sweet diesel) and think ‘what the hell is that?’ it turned out that it was coming from a tarmac factory hidden in a quarry on the other side of the hill. When the wind was in a certain direction it would blow the fumes over our way or certain atmospheric conditions made it worse. It seemed to be particularly bad in the morning.
I approached our council and asked them to take tests – it took ages for them to agree but even then they would only monitor it from the road which was 0.5 kilometres away. I hope you get some help finding out what it is.