Consider Hong Kong atmosphere as a box including emissions of SO 2
​
,NO x
​
, and NH 3
​
. Denote these emissions as E SO2
​
,E NO
​
,E NH3
​
in units of moles per year. Assume that all emitted SO 2
​
is converted to sulfate inside the box, that all emitted NO x
​
is converted to HNO 3
​
inside the box, that all removal from the box is by deposition, and that all species have the same lifetime against deposition. We consider in that system the formation of SNA aerosols to answer the following questions: (a) Will ammonium nitrate aerosol form in the system if the emissions satisfy the condition E NH3
​
<2E SO2
​
. Briefly explain why. (b) If 2E SO2
​
+E NOx
​
>E NH3
​
>2E SO 2
​
​
, is the formation of NH 4
​
NO 3
​
aerosol limited by the supply of NH 3
​
, or by the supply of NO x
​
? (c) Under the conditions of (b), will decreasing SO 2
​
emissions cause an increase or decrease in total aerosol mass concentrations? Briefly explain why.