Use the Ideal gas Law, which is Pv=nRT.p=pressure(in atm)v=volume(in liters)n=moles(per gram)R=constant(0.0821 [(Liters x atm)/(K x mol)]t=temperature(in kelvin)find the values of each and solve for...
Since both of them are per liter....then all you need to do is a one step conversion of moles into grams using the molar mass...essentially you are going to multiply the mol/L by the molar mass in...
1 microgram = 1 millionth of a gram or .000001 - so, just move the decimal point over to the appropriate position. As long as you don't change the value of the number, you can do what you want to it.