雜質                                      來源                                       地點                 正常范圍（1X10^-3mg/m³）
                 NH₄                  礦物燃料，森林有機物的腐爛             海洋空氣             0.04-0.29
                                                                                                               內陸空氣               0.10-0.76
                   
                  NO₃                             工業過程及內燃機                      海洋空氣             0.3-5
                                                                                                               內陸空氣              0.10-0.6

                 CL                        海鹽，土壤顆粒海洋空氣                  海洋空氣             0.10-0.5
                                                                                                               內陸空氣            1-20