The amount of dust contained in a given unit of air; this quantity can be either a number or a mass.

【Reference】 Dust concentration specifically refers to the number of suspended particles per unit volume of air.

【Reference】 There are three methods for expressing atmospheric dust concentration (Table 1.1).

(1) Number concentration: expressed by the number of dust particles contained in a unit volume of air, denoted as particles/$m^3$ or particles/L.

(2) Mass concentration: expressed by the mass of dust particles contained in a unit volume of air, denoted as mg/$m^3$.

(3) Settling concentration: expressed by the number or mass of dust particles naturally settling onto a unit area per unit time, denoted as particles/($cm^2cdot$ h) or t/($km^2cdot$ month).

Table 1.1 Comparison of several concentrations

Dust concentration Industrial cities (polluted areas) Suburbs of industrial cities (intermediate areas) Non-industrial areas or rural areas (clean areas) Cleanroom for the production of large-scale integrated circuits Production of passive laser night-vision instruments
$geqslant 0.5mu m$ number concentration/(particles/L) $leqslant 3times 10^5$ $leqslant 2times 10^5$ $leqslant 10^5$ $leqslant 3$ $leqslant 0.3$
Mass concentration/(mg/$m^3$) 0.3~1 0.1~0.3 <0.1
Settling concentration/[t/($km^2cdot$ month)] >15 <15 <5

【Reference】 Since the numbers of particles in different size ranges of atmospheric dust differ too greatly, the particle size range must be indicated when using number concentration; the most commonly used is the number concentration based on the number of particles $geqslant 0.5mu m$. Mass concentration and settling concentration do not need to indicate the particle size range.