Environmental temperature and humidity are key factors affecting the sampling efficiency of air microbial samplers. They directly affect the sampling efficiency (the proportion of captured microorganisms), microbial survival rate (the number of cultivable microorganisms after sampling), and the accuracy of the final detection results by changing the microbial activity, air fluid characteristics, and core component functions of the sampler. The specific impact mechanism is as follows:

1、 The Influence of Temperature on Sampling Efficiency: The Core Role of "Microbial Activity" and "Air Physical Characteristics"

Temperature indirectly affects the capture and retention of microorganisms by samplers by altering their physiological state (survival/inactivation) and the density and viscosity of air

1. High temperature environment (usually>35 ℃): reduces microbial survival rate, may decrease sampling efficiency

Microbial survival rate decreases:

The suitable survival temperature for most airborne microorganisms (such as bacteria and fungal spores) is 20-30 ℃. High temperatures can accelerate microbial protein denaturation and nucleic acid damage - for example, when sampling at 40 ℃, the survival rate of bacteria (such as Escherichia coli and Staphylococcus) may drop from 80% at room temperature to below 30%, resulting in a much lower "number of colonies cultured after sampling" than the actual number of microorganisms in the air, leading to "false negatives" or "low results".

Especially for "non spore forming microorganisms" (such as influenza viruses and yeast), the inactivation rate is faster at high temperatures, and it is almost impossible to detect them through subsequent cultivation.

Changes in air physical properties affect sampling and capture efficiency:

An increase in temperature will cause a decrease in air density and viscosity (such as an air density of 1.205kg/m ³ at 20 ℃, which drops to 1.145kg/m ³ at 35 ℃). If the sampler is an "impact type" (such as the Anderson sampler, which impacts microorganisms onto the culture medium through high-speed airflow), a decrease in air viscosity may cause a slight increase in airflow velocity, which may result in some small microbial particles (such as virus particles<1 μ m) being unable to effectively impact the surface of the culture medium due to insufficient inertia and instead escaping with the airflow, reducing sampling efficiency.

2. Low temperature environment (usually<10 ℃): inhibits microbial metabolism and increases the risk of sampler component failure

Microbial metabolism inhibition, survival but difficult to cultivate:

Low temperature can inhibit the enzyme activity of microorganisms, causing them to enter a "dormant state" (such as fungal spores and Bacillus). Although they will not be inactivated in the short term, if they are directly cultured under conventional conditions (such as 37 ℃ constant temperature culture) after sampling, the recovery speed of dormant microorganisms will be slow, which may lead to "insufficient colony count when the cultivation time is not enough" and be mistakenly judged as "low concentration of microorganisms in the air".

For example, bacteria sampled in a 5 ℃ environment need to be cultured for an extended period of time (from 24 hours to 48 hours) to restore their activity, otherwise the test results will be 30% -50% lower.

Sampler component malfunction:

If the sampler contains "airflow control components" (such as flow meters, pump body seals), low temperatures may cause the rubber seals to harden, and the viscosity of the liquid inside the flow meter (such as the working fluid of a rotor flow meter) to increase, affecting the stability of the airflow - for example, the flow meter displays a sampling flow rate of 28.3 L/min (standard flow rate), but in reality, due to the increase in liquid viscosity, the flow rate drops to 25 L/min, resulting in a decrease in the capture of microbial particles per unit time and a systematic low sampling result.

2、 The Influence of Humidity on Sampling Efficiency: The Core Role of "Microbial Particle Morphology" and "Sampling Capture Mechanism"

Humidity directly affects sampling efficiency and microbial survival by altering the "particle aggregation state" of air microorganisms (individual particles vs. aggregated particles) and the "adsorption capacity of sampling media" (such as the moisture absorption capacity of culture media and filter membranes)

1. High humidity environment (relative humidity RH>80%): Microbial particles agglomerate, and the sampling medium fails to absorb moisture

Microbial particle aggregation and fluctuation in capture efficiency:

In high humidity environments, tiny microbial particles in the air (such as 1-5 μ m bacteria and fungal spores) will "aggregate" due to the condensation of water vapor, forming larger particle clusters (such as 5-10 μ m).

For the "impact sampler": large particle clusters have greater inertia and are more likely to impact the surface of the culture medium, which may increase sampling efficiency in the short term (such as when RH=90%, the impact efficiency is 20% higher than when RH=50%); However, if the agglomerated particles are too large (>10 μ m), they may be intercepted by the "pre filter" of the sampler (used to filter dust) and unable to enter the sampling area, resulting in a decrease in efficiency.

For "filter membrane samplers" (such as microporous filters capturing microorganisms): Agglomerated particles are prone to clogging the pore size of the filter membrane (such as 0.45 μ m filter membrane being blocked by 5 μ m aggregated particles), resulting in increased airflow resistance, decreased flow rate in the later stage of sampling, reduced microbial capture, and distorted results.

The moisture absorption of the sampling medium affects the survival and cultivation of microorganisms

High humidity can cause the "culture medium" (such as the agar plate of an impact sampler) or "adsorption medium" (such as a filter membrane) of the sampler to absorb excessive moisture - the agar culture medium will soften and liquefy after absorbing moisture, and microorganisms are prone to spread with the liquid after impact, resulting in "colony overlap" (multiple microorganisms forming a large colony), which cannot be accurately counted; After absorbing moisture, the filter membrane will enhance its adsorption capacity for microorganisms, but excessive wetting may lead to an anaerobic environment, causing aerobic microorganisms (such as most bacteria) to become inactive and their survival rate to decrease.

2. Low humidity environment (relative humidity RH<30%): Microorganisms dehydrate and become inactive, and particles are prone to electrostatic adsorption

Microbial dehydration and inactivation lead to a sharp decline in survival rate:

In a low humidity environment, the air humidity is much lower than the water activity inside microbial cells (most microorganisms require a water activity of>0.85), and microorganisms will rapidly dehydrate (such as bacterial cell wall wrinkling and viral capsid denaturation), especially "spore free/capsule free microorganisms" (such as Streptococcus pneumoniae and influenza virus). After sampling in an RH=20% environment, the survival rate may be less than 10%, leading to severely low test results.

Even drought tolerant fungal spores (such as Aspergillus spores) can experience a decrease in germination rate and colony count during cultivation due to dehydration when exposed to low humidity environments for a long time.

Microbial particles carry static electricity and adsorb and lose:

In low humidity environments, the conductivity of air is poor, and microbial particles (especially non-polar fungal spores and virus particles) are prone to static electricity due to friction (such as friction with air molecules and the inner wall of the sampler), which then adsorbs onto the "inlet pipe wall", "flow meter inner wall" or "filter membrane support" of the sampler, and cannot reach the sampling medium (such as culture medium, filter membrane). For example, at RH=25%, about 30% of 1 μ m bacterial particles will be electrostatically adsorbed onto the inlet pipe wall, resulting in an actual capture amount of only 70% of the theoretical value, and the result deviation is significant.