Concentration to AQI calculation for US and China.

Adafruit_PM25AQI.cpp

@@ -29,6 +29,7 @@
  */
 
 #include "Adafruit_PM25AQI.h"
+#include <math.h>
 
 /*!
  *  @brief  Instantiates a new PM25AQI class
@@ -126,7 +127,7 @@ bool Adafruit_PM25AQI::read(PM25_AQI_Data *data) {
   }
 
   // Validate start byte is correct if using Adafruit PM sensors
-  if ((!is_pm1006 && buffer[0] != 0x42)) {
+  if ((!is_pm1006 && (buffer[0] != 0x42 || buffer[1] != 0x4d))) {
     return false;
   }
 
@@ -168,6 +169,160 @@ bool Adafruit_PM25AQI::read(PM25_AQI_Data *data) {
     return false;
   }
 
+  // convert concentration to AQI
+  data->aqi_pm25_us = pm25_aqi_us(data->pm25_env);
+  data->aqi_pm25_china = pm25_aqi_china(data->pm25_env);
+  data->aqi_pm100_us = pm100_aqi_us(data->pm100_env);
+  data->aqi_pm100_china = pm100_aqi_china(data->pm100_env);
+
   // success!
   return true;
 }
+
+/*!
+ *  @brief  Get AQI of PM2.5 in US standard
+ *  @param  concentration
+ *          the environmental concentration of pm2.5 in ug/m3
+ *  @return AQI number. 0 to 500 for valid calculation. 99999 for out of range.
+ */
+uint16_t Adafruit_PM25AQI::pm25_aqi_us(float concentration) {
+  float c;
+  float AQI;
+  c = (floor(10 * concentration)) / 10;
+  if (c < 0)
+    AQI = 0;
+  else if (c >= 0 && c < 12.1f) {
+    AQI = linear(50, 0, 12, 0, c);
+  } else if (c >= 12.1f && c < 35.5f) {
+    AQI = linear(100, 51, 35.4f, 12.1f, c);
+  } else if (c >= 35.5f && c < 55.5f) {
+    AQI = linear(150, 101, 55.4f, 35.5f, c);
+  } else if (c >= 55.5f && c < 150.5f) {
+    AQI = linear(200, 151, 150.4f, 55.5f, c);
+  } else if (c >= 150.5f && c < 250.5f) {
+    AQI = linear(300, 201, 250.4f, 150.5f, c);
+  } else if (c >= 250.5f && c < 350.5f) {
+    AQI = linear(400, 301, 350.4f, 250.5f, c);
+  } else if (c >= 350.5f && c < 500.5f) {
+    AQI = linear(500, 401, 500.4f, 350.5f, c);
+  } else {
+    AQI = 99999; //
+  }
+  return round(AQI);
+}
+
+/*!
+ *  @brief  Get AQI of PM10 in US standard
+ *  @param  concentration
+ *          the environmental concentration of pm10 in ug/m3
+ *  @return AQI number. 0 to 500 for valid calculation. 99999 for out of range.
+ */
+uint16_t Adafruit_PM25AQI::pm100_aqi_us(float concentration) {
+  float c;
+  float AQI;
+  c = concentration;
+  if (c < 0)
+    AQI = 0;
+  else if (c < 55) {
+    AQI = linear(50, 0, 55, 0, c);
+  } else if (c < 155) {
+    AQI = linear(100, 51, 155, 55, c);
+  } else if (c < 255) {
+    AQI = linear(150, 101, 255, 155, c);
+  } else if (c < 355) {
+    AQI = linear(200, 151, 355, 255, c);
+  } else if (c < 425) {
+    AQI = linear(300, 201, 425, 355, c);
+  } else if (c < 505) {
+    AQI = linear(400, 301, 505, 425, c);
+  } else if (c < 605) {
+    AQI = linear(500, 401, 605, 505, c);
+  } else {
+    AQI = 99999; //
+  }
+  return round(AQI);
+}
+
+/*!
+ *  @brief  Get AQI of PM2.5 in China standard
+ *  @param  concentration
+ *          the environmental concentration of pm2.5 in ug/m3
+ *  @return AQI number. 0 to 500 for valid calculation. 99999 for out of range.
+ */
+uint16_t Adafruit_PM25AQI::pm25_aqi_china(float concentration) {
+  float c;
+  float AQI;
+  c = concentration;
+  if (c < 0)
+    AQI = 0;
+  else if (c <= 35) {
+    AQI = linear(50, 0, 35, 0, c);
+  } else if (c <= 75) {
+    AQI = linear(100, 51, 75, 35, c);
+  } else if (c <= 115) {
+    AQI = linear(150, 101, 115, 75, c);
+  } else if (c <= 150) {
+    AQI = linear(200, 151, 150, 115, c);
+  } else if (c <= 250) {
+    AQI = linear(300, 201, 250, 150, c);
+  } else if (c <= 350) {
+    AQI = linear(400, 301, 350, 250, c);
+  } else if (c <= 500) {
+    AQI = linear(500, 401, 500, 350, c);
+  } else {
+    AQI = 99999; //
+  }
+  return round(AQI);
+}
+
+/*!
+ *  @brief  Get AQI of PM10 in China standard
+ *  @param  concentration
+ *          the environmental concentration of pm10 in ug/m3
+ *  @return AQI number. 0 to 500 for valid calculation. 99999 for out of range.
+ */
+uint16_t Adafruit_PM25AQI::pm100_aqi_china(float concentration) {
+  float c;
+  float AQI;
+  c = concentration;
+  if (c < 0)
+    AQI = 0;
+  else if (c <= 50) {
+    AQI = linear(50, 0, 50, 0, c);
+  } else if (c <= 150) {
+    AQI = linear(100, 51, 150, 50, c);
+  } else if (c <= 250) {
+    AQI = linear(150, 101, 250, 150, c);
+  } else if (c <= 350) {
+    AQI = linear(200, 151, 350, 250, c);
+  } else if (c <= 420) {
+    AQI = linear(300, 201, 420, 350, c);
+  } else if (c <= 500) {
+    AQI = linear(400, 301, 500, 420, c);
+  } else if (c <= 600) {
+    AQI = linear(500, 401, 600, 500, c);
+  } else {
+    AQI = 99999; //
+  }
+  return round(AQI);
+}
+
+/*!
+ *  @brief  Linearly map a concentration value to its AQI level
+ *  @param  aqi_high max aqi of the calculating range
+ *  @param  aqi_low min aqi of the calculating range
+ *  @param  conc_high max concentration value (ug/m3) of the calculating range
+ *  @param  conc_low min concentration value (ug/m3) of the calculating range
+ *  @param  concentration
+ *          the concentration value to be calculated
+ *  @return Calculated AQI value
+ */
+float Adafruit_PM25AQI::linear(uint16_t aqi_high, uint16_t aqi_low,
+                               float conc_high, float conc_low,
+                               float concentration) {
+  float f;
+  f = ((concentration - conc_low) / (conc_high - conc_low)) *
+          (aqi_high - aqi_low) +
+      aqi_low;
+  return f;
+}

Adafruit_PM25AQI.h

@@ -41,8 +41,16 @@ typedef struct PMSAQIdata {
       particles_25um,      ///< 2.5um Particle Count
       particles_50um,      ///< 5.0um Particle Count
       particles_100um;     ///< 10.0um Particle Count
-  uint16_t unused;         ///< Unused
-  uint16_t checksum;       ///< Packet checksum
+  uint16_t unused;         ///< Unused (version + error code)
+
+  uint16_t checksum; ///< Packet checksum
+
+  // AQI conversion results:
+  uint8_t aqi_pm25_us;     ///< pm2.5 AQI of United States
+  uint8_t aqi_pm100_us;    ///< pm10 AQI of United States
+  uint8_t aqi_pm25_china;  ///< pm2.5 AQI of China
+  uint8_t aqi_pm100_china; ///< pm10 AQI of China
+
 } PM25_AQI_Data;
 
 /*!
@@ -56,6 +64,13 @@ class Adafruit_PM25AQI {
   bool begin_UART(Stream *theStream);
   bool read(PM25_AQI_Data *data);
 
+  uint16_t pm25_aqi_us(float concentration);
+  uint16_t pm25_aqi_china(float concentration);
+  uint16_t pm100_aqi_us(float concentration);
+  uint16_t pm100_aqi_china(float concentration);
+  float linear(uint16_t aqi_high, uint16_t aqi_low, float conc_high,
+               float conc_low, float concentration);
+
 private:
   Adafruit_I2CDevice *i2c_dev = NULL;
   Stream *serial_dev = NULL;

examples/PM25_test/PM25_test.ino

@@ -42,20 +42,19 @@ void loop() {
 
   if (! aqi.read(&data)) {
     Serial.println("Could not read from AQI");
+
     delay(500);  // try again in a bit!
     return;
   }
   Serial.println("AQI reading success");
 
-  Serial.println();
   Serial.println(F("---------------------------------------"));
   Serial.println(F("Concentration Units (standard)"));
-  Serial.println(F("---------------------------------------"));
   Serial.print(F("PM 1.0: ")); Serial.print(data.pm10_standard);
   Serial.print(F("\t\tPM 2.5: ")); Serial.print(data.pm25_standard);
   Serial.print(F("\t\tPM 10: ")); Serial.println(data.pm100_standard);
-  Serial.println(F("Concentration Units (environmental)"));
   Serial.println(F("---------------------------------------"));
+  Serial.println(F("Concentration Units (environmental)"));
   Serial.print(F("PM 1.0: ")); Serial.print(data.pm10_env);
   Serial.print(F("\t\tPM 2.5: ")); Serial.print(data.pm25_env);
   Serial.print(F("\t\tPM 10: ")); Serial.println(data.pm100_env);
@@ -67,7 +66,13 @@ void loop() {
   Serial.print(F("Particles > 5.0um / 0.1L air:")); Serial.println(data.particles_50um);
   Serial.print(F("Particles > 10 um / 0.1L air:")); Serial.println(data.particles_100um);
   Serial.println(F("---------------------------------------"));
-
+  Serial.println(F("AQI"));
+  Serial.print(F("PM2.5 AQI US: ")); Serial.print(data.aqi_pm25_us);
+  Serial.print(F("\tPM10  AQI US: ")); Serial.println(data.aqi_pm100_us);
+//  Serial.print(F("PM2.5 AQI China: ")); Serial.print(data.aqi_pm25_china);
+//  Serial.print(F("\tPM10  AQI China: ")); Serial.println(data.aqi_pm100_china);
+  Serial.println(F("---------------------------------------"));
+  Serial.println();
 
   delay(1000);
-}
+}