AQI: Adding ugm3 calculation to ppd42ns and aqi calculation to upm_utilities

Contributions by: Rex Tsai <rex.cc.tsai@gmail.com>

Signed-off-by: Abhishek Malik <abhishek.malik@intel.com>

src/ppd42ns/ppd42ns.c

@@ -1,5 +1,7 @@
 /*
  * Author: Jon Trulson <jtrulson@ics.com>
+ * Contributions: Rex Tsai <rex.cc.tsai@gmail.com>
+ *                Abhishek Malik <abhishek.malik@intel.com>
  * Copyright (c) 2016 Intel Corporation.
  *
  * Rewritten Based on original C++ driver written by:
@@ -39,6 +41,7 @@
 // from LOW to HIGH
 static uint32_t ppd42ns_pulse_in(const ppd42ns_context dev,
                                  bool high_low_value);
+double pcs2ugm3 (double concentration_pcs);
 
 ppd42ns_context ppd42ns_init(int pin)
 {
@@ -112,6 +115,8 @@ ppd42ns_dust_data ppd42ns_get_data(const ppd42ns_context dev)
     data.lowPulseOccupancy = low_pulse_occupancy;
     data.ratio = ratio;
     data.concentration = concentration;
+    data.ugm3 = pcs2ugm3(data.concentration);
+    data.aqi = upm_ugm3_to_aqi(data.ugm3);
 
     return data;
 }
@@ -165,3 +170,26 @@ static uint32_t ppd42ns_pulse_in(const ppd42ns_context dev,
 
     return total_pulse_time;
 }
+
+// Assumes density, shape, and size of dust to estimate mass concentration from particle count.
+//
+// This method was described in a 2009 paper
+// Preliminary Screening System for Ambient Air Quality in Southeast Philadelphia by Uva, M., Falcone, R., McClellan, A., and Ostapowicz, E.
+// https://www.yumpu.com/en/document/view/31692906/preliminary-screening-system-for-ambient-air-quality-in-southeast-
+//
+// This method does not use the correction factors, based on the presence of humidity and rain in the paper.
+//
+// convert from particles/0.01 ft3 to µg/m3
+double pcs2ugm3 (double concentration_pcs)
+{
+    double pi = 3.14159;
+    // All particles are spherical, with a density of 1.65E12 µg/m3
+    double density = 1.65 * pow (10, 12);
+    // The radius of a particle in the PM2.5 channel is .44 µm
+    double r25 = 0.44 * pow (10, -6);
+    double vol25 = (4/3) * pi * pow (r25, 3);
+    double mass25 = density * vol25; // ug
+    double K = 3531.5; // per m^3 
+
+    return concentration_pcs * K * mass25;
+}

src/ppd42ns/ppd42ns_data.h

@@ -1,5 +1,7 @@
 /*
  * Author: Jon Trulson <jtrulson@ics.com>
+ * Contributions: Rex Tsai <rex.cc.tsai@gmail.com>
+ *                Abhishek Malik <abhishek.malik@intel.com>
  * Copyright (c) 2016 Intel Corporation.
  *
  * Based on original C++ driver written by:
@@ -37,6 +39,8 @@ extern "C" {
 	unsigned int lowPulseOccupancy;
 	double ratio;
 	double concentration;
+    double ugm3;
+	int aqi;
     } ppd42ns_dust_data;
 
 #ifdef __cplusplus

src/utilities/upm_utilities.c

@@ -1,7 +1,9 @@
 /*
  * Authors:
  *          Jon Trulson <jtrulson@ics.com>
- * Copyright (c) 2016 Intel Corporation.
+ * Contributions: Rex Tsai <rex.cc.tsai@gmail.com>
+ *                Abhishek Malik <abhishek.malik@intel.com>
+ * Copyright (c) 2017 Intel Corporation.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -32,6 +34,22 @@
 #include <upm_platform.h>
 #include <upm_utilities.h>
 
+// https://airnow.gov/index.cfm?action=aqibasics.aqi
+static struct aqi {
+    float clow;
+    float chigh;
+    int llow;
+    int lhigh;
+} aqi[] = {
+  {0.0,    12.4,   0, 50},
+  {12.1,   35.4,  51, 100},
+  {35.5,   55.4, 101, 150},
+  {55.5,  150.4, 151, 200},
+  {150.5, 250.4, 201, 300},
+  {250.5, 350.4, 301, 350},
+  {350.5, 500.4, 401, 500},
+};
+
 void upm_delay(unsigned int time)
 {
     if (time <= 0)
@@ -246,3 +264,19 @@ uint32_t upm_elapsed_us(upm_clock_t *clock)
     return elapsed;
 #endif
 }
+
+int upm_ugm3_to_aqi (double ugm3)
+{
+  int i;
+
+  for (i = 0; i < 7; i++) {
+    if (ugm3 >= aqi[i].clow &&
+        ugm3 <= aqi[i].chigh) {
+        // Ip =  [(Ihi-Ilow)/(BPhi-BPlow)] (Cp-BPlow)+Ilow,
+        return ((aqi[i].lhigh - aqi[i].llow) / (aqi[i].chigh - aqi[i].clow)) * 
+            (ugm3 - aqi[i].clow) + aqi[i].llow;
+    }
+  }
+
+  return 0;
+}

src/utilities/upm_utilities.h

@@ -1,7 +1,9 @@
 /*
  * Authors:
  *          Jon Trulson <jtrulson@ics.com>
- * Copyright (c) 2016 Intel Corporation.
+ * Contributions: Rex Tsai <rex.cc.tsai@gmail.com>
+ *                Abhishek Malik <abhishek.malik@intel.com>
+ * Copyright (c) 2017 Intel Corporation.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -113,6 +115,15 @@ uint32_t upm_elapsed_ms(upm_clock_t *clock);
  */
 uint32_t upm_elapsed_us(upm_clock_t *clock);
 
+/**
+ * Return the AQI (based on EPA standards) using the ugm3 value
+ * calculated by the sensor module.
+ *
+ * @param ugm3 micrograms per cubic meter
+ * @return calculated AQI
+ */
+int upm_ugm3_to_aqi (double ugm3);
+
 #ifdef __cplusplus
 }
 #endif