How can I calibrate the DSM501A sensor

[sebavfghj]

Hello, I am testing the DSM501A sensor and using NodeMCU ESP8266, usually getting values equal to -0.5 mg/m3, but sometimes these values go up to 0.02 mg/m3 and even 0.5 mg/m3.
I sincerely doubt the veracity of the last information mentioned. I placed the sensor on a desk that is next to an air conditioner, about a meter and a half away.
At the end of the day I would like to use this sensor to check the concentration of dust and pollen.
Below I am attaching the datasheet and code I am using.
Datasheet: https://www.elektronik.ropla.eu/pdf/stock/smy/dsm501.pdf

#include<string.h>
#define PM25PIN D7 //el pin 4 del DSM501A
byte buff[2];
//unsigned long durationPM1;
unsigned long durationPM25;
unsigned long starttime;
unsigned long endtime;
unsigned long sampletime_ms = 30000;
unsigned long lowpulseoccupancyPM25 = 0;

 
int i=0;
void setup()
{
  Serial.begin(9600);
  Serial.println("Starting please wait 30s");
  pinMode(PM25PIN,INPUT);
  starttime = millis(); 
}

float calculateConcentration(long lowpulseInMicroSeconds, long durationinSeconds){
  
  float ratio = (lowpulseInMicroSeconds/1000000.0)/30.0*100.0; 
  float concentration = 0.001915 * pow(ratio,2) + 0.09522 * ratio - 0.04884;//esta en mg/m3
  Serial.print("lowpulseoccupancy:");
  Serial.print(lowpulseInMicroSeconds);
  Serial.print("    ratio:");
  Serial.print(ratio);
  Serial.print("    Concentration:");
  Serial.println(concentration);
  return concentration;
}

void loop()
{
  durationPM25 = pulseIn(PM25PIN, LOW);
  
  lowpulseoccupancyPM25 += durationPM25;
  
  endtime = millis();
  if ((endtime-starttime) > sampletime_ms) //Only after 30s has passed we calcualte the ratio
  {
    /*
    ratio1 = (lowpulseoccupancy/1000000.0)/30.0*100.0; //Calculate the ratio
    Serial.print("ratio1: ");
    Serial.println(ratio1);
    
    concentration = 0.001915 * pow(ratio1,2) + 0.09522 * ratio1 - 0.04884;//Calculate the mg/m3
    */
    float conPM25 = calculateConcentration(lowpulseoccupancyPM25,30);
    float conUG=conPM25*1000;//calculate ug/m3
    Serial.print("  PM25 ");
    Serial.println(conPM25 +"mg/m3");
    Serial.println(String(conUG)+"ug/m3");
    lowpulseoccupancyPM25 = 0;
    starttime = millis();
  } 
}