SMOG = unhealthy plants

If you live near a busseling metropolis are have code orange and higher smog alerts in your area. You plants are being affected by this also. It has happened to me this year, (unbelievably bad smog), my healthy plants that have damn near perfect growing conditions are having a little yellowing or browning of the older leaves, then they will start to droop a little. So if you are like me, and know your plant had all the right conditions but still have a few older leaves looking rough, rest assured its nothing we can control. (on a growers level)

How do you know its the smog killing your plants... Unless you've done some serious soil/water/air tests there is no way of determining that it was the smog... this sounds like speculation but it is a possibility.