對環境大氣（空氣）中污染物濃度的表示方法有兩種：
   1、質量濃度表示法：每立方米空氣中所含污染物的質量數，即mg/m3 
   2、體(ti)(ti)(ti)積(ji)(ji)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)表(biao)示法：一百萬(wan)體(ti)(ti)(ti)積(ji)(ji)的(de)(de)空(kong)氣(qi)中所含污(wu)(wu)染(ran)(ran)(ran)(ran)物的(de)(de)體(ti)(ti)(ti)積(ji)(ji)數(shu)，即ppm 大部(bu)分(fen)氣(qi)體(ti)(ti)(ti)檢(jian)測(ce)儀器(qi)測(ce)得的(de)(de)氣(qi)體(ti)(ti)(ti)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)都(dou)是(shi)(shi)體(ti)(ti)(ti)積(ji)(ji)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)（ppm）。而(er)按我(wo)國規(gui)定，特別是(shi)(shi)環(huan)保部(bu)門(men)，則要求氣(qi)體(ti)(ti)(ti)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)以質量(liang)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)的(de)(de)單(dan)(dan)位(wei)（如(ru)：mg/m3）表(biao)示，我(wo)們國家的(de)(de)標準規(gui)范也(ye)都(dou)是(shi)(shi)采用質量(liang)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)單(dan)(dan)位(wei)（如(ru)：mg/m3）表(biao)示。 這兩(liang)種氣(qi)體(ti)(ti)(ti)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)單(dan)(dan)位(wei)mg/m3與ppm有(you)(you)何關系呢(ni)？其(qi)間如(ru)何換(huan)算(suan)？ 使(shi)用質量(liang)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)單(dan)(dan)位(wei)（mg/m3）作(zuo)為空(kong)氣(qi)污(wu)(wu)染(ran)(ran)(ran)(ran)物濃(nong)(nong)(nong)(nong)(nong)度(du)(du)的(de)(de)表(biao)示方法，可以方便計(ji)算(suan)出(chu)污(wu)(wu)染(ran)(ran)(ran)(ran)物的(de)(de)真正量(liang)。但質量(liang)濃(nong)(nong)(nong)(nong)(nong)度(du)(du)與檢(jian)測(ce)氣(qi)體(ti)(ti)(ti)的(de)(de)溫度(du)(du)、壓(ya)力環(huan)境(jing)條件有(you)(you)關，其(qi)數(shu)值會(hui)隨(sui)著(zhu)溫度(du)(du)、氣(qi)壓(ya)等(deng)環(huan)境(jing)條件的(de)(de)變化而(er)不(bu)同(tong)；實際測(ce)量(liang)時(shi)(shi)需(xu)要同(tong)時(shi)(shi)測(ce)定氣(qi)體(ti)(ti)(ti)的(de)(de)溫度(du)(du)和大氣(qi)壓(ya)力。而(er)在使(shi)用ppm作(zuo)為描述(shu)污(wu)(wu)染(ran)(ran)(ran)(ran)物濃(nong)(nong)(nong)(nong)(nong)度(du)(du)時(shi)(shi)，由于采取的(de)(de)是(shi)(shi)體(ti)(ti)(ti)積(ji)(ji)比，不(bu)會(hui)出(chu)現這個問(wen)題。 

濃度單位ppm與mg/m3的換算：
    按下(xia)式(shi)計算： 質量(liang)(liang)(liang)濃(nong)度(du)mg/m3=M氣(qi)體分(fen)子(zi)(zi)(zi)量(liang)(liang)(liang)/22.4*ppm數值*[273/(273+T氣(qi)體溫度(du))]*（Ba壓力/101325）M為(wei)(wei)(wei)氣(qi)體分(fen)子(zi)(zi)(zi)量(liang)(liang)(liang)，ppm為(wei)(wei)(wei)測定的(de)體積濃(nong)度(du)值，T為(wei)(wei)(wei)溫度(du)、Ba為(wei)(wei)(wei)壓力，如果濕(shi)度(du)很大時，例(li)如在(zai)100%相對濕(shi)度(du)下(xia)，還(huan)需另(ling)外一項。氣(qi)體分(fen)子(zi)(zi)(zi)量(liang)(liang)(liang)?從哪得來？別(bie)急！我(wo)們有(you)個氣(qi)體分(fen)子(zi)(zi)(zi)量(liang)(liang)(liang)的(de)計算軟(ruan)件(jian)呢---只要你把該(gai)氣(qi)體的(de)分(fen)子(zi)(zi)(zi)式(shi)一輸入(ru)，馬上就得到(dao)其氣(qi)體分(fen)子(zi)(zi)(zi)量(liang)(liang)(liang)！神吧！下(xia)載氣(qi)體分(fen)子(zi)(zi)(zi)量(liang)(liang)(liang)計算軟(ruan)件(jian): ---本軟(ruan)件(jian)支持所化(hua)(hua)學(xue)(xue)領(ling)域可能會出現的(de)化(hua)(hua)學(xue)(xue)式(shi)，支持含有(you)中(zhong)、小括號(hao)(hao)的(de)化(hua)(hua)學(xue)(xue)式(shi)（可嵌套），支持有(you)機(ji)化(hua)(hua)合物中(zhong)單鍵、雙鍵、叁鍵符號(hao)(hao)的(de)輸入(ru)，支持含有(you)非整數的(de)系數與角(jiao)標的(de)化(hua)(hua)學(xue)(xue)式(shi)，支持含有(you)同位素符號(hao)(hao)的(de)化(hua)(hua)學(xue)(xue)式(shi)，等等。計算結果將給出式(shi)量(liang)(liang)(liang)、zui簡式(shi)、元素含量(liang)(liang)(liang)統計。[常見氣(qi)體分(fen)子(zi)(zi)(zi)量(liang)(liang)(liang)： 甲醛(quan)HCHO為(wei)(wei)(wei)30.0260，苯C6H6為(wei)(wei)(wei)78.1118，氨NH3為(wei)(wei)(wei)17.0306