Real English Seven-unless

On Thursday, Kyoko called me in the morning. She never calls me in the day time unless there is a problem, so when I saw her number on the screen of my i-phone, I thought "What happened now?" and answered the phone.

Me:  Hi. What's wrong?
Kyoko: I can't see the mountains because of that PM2.5!  And I checked the Nishinomiya City Home Page...it said that the government issued a pollution warning and advised everyone to 'refrain from going out unless you have to'.  What do you think that means?
Me:  That means that if you don't have to go out, you shouldn't.  Or in other words, you should go out only if you have to.
Kyoko:  Got it.  How was it outside when you left this morning?
Me: It was still dark so I don't know
Kyoko:  How is Osaka now?
Me:  It is kinda hazy...
Kyoko:  What do you think? Do you think I can go out today?  Or should I just bag it?
Me:  I don't think it will be a problem if you go out for 30 minutes or so.
Kyoko:  I don't know...But, if possible, I want to go out for a little in the afternoon, so I will wait and see if it clears up.
Me:  Good idea! By the way, do you know what 'PM' stands for?
Kyoko:  No.
Me: Do you want to know?  Do you want me to teach you?
Kyoko: Yes, please!
Me: 'P' stands for 'Particle'. and 'M' stands for 'Matter.' So, 'Particle matter.'
Kyoko:  Thanks so much for teaching me that! What does the '2.5' mean?
Me: I don't know. Google it! 
Kyoko:  Have a good day!
Me: You too!