Photon blinking red when i dont write in the console

Hardware
4

As I said four characters will not fit into your array and there you have four.
The potential for negatives may not be there in real life but since you don't check whether the sensor provides valid data via the result you can never be certain to not get a negative reading or a reading > 99.9°C. Hence it does make sense to point out the fact.
A programmer has to expect the unexpected, even the impossible has to be considered!

Hard to tell, but one possibility is that the corrupting call affects some memory location which the Particle.publish() call doesn't care about and may even rectify by being called (especially the state of the stack springs to mind).
When removing that call, the subsequent call may not be as resilient and crash.

While I could come up with several other possible explanations, there is little use in doing so, as it doesn't matter. Erroneous code needs to be corrected in any case, no matter why it crashes. It even needs correcting when it doesn't crash at all.

And I have suggested what to do :wink:

  • use snprintf()
  • address the too small buffer problem

While at it, incorporate the other suggestions to adopt better coding practices.

This would be my take on this 
#include <MQTT.h>
#include <PietteTech_DHT.h>
#include <DustSensor.h>

const char      mqttADDR[]  = "192.168.1.12";
const char      mqttTOPIC[] = "photon";
const char      mqttUSER[]  = "User";
const char      mqttPWD[]   = "Pwd";
const char      mqttINFO[]  = "environment";
const int       dhtTYPE     = DHT22;
const int       dhtPIN      = D4;
const uint32_t  msDELAY     = 100;

float           temp;                   // temperature in [°C]
float           hum;                    // relative humidity in [%]
char            envData[128];           // string for Particle.variable and MQTT publish

pms5003data     pmsData;

MQTT            client(mqttADDR, 1883, [](char* topic, byte* payload, unsigned int length) {});  // don't care to receive data (empty lambda)
PietteTech_DHT  DHT(dhtPIN, dhtTYPE);
DustSensor      dustSensor;

void setup() {
  dustSensor.begin();
  Particle.variable(mqttINFO, envData);
  client.connect(mqttTOPIC, mqttUSER, mqttPWD);
}

void loop() {
  static uint32_t ms = 0;
  if (millis() - ms < msDELAY) return;
  ms = millis();
  
  readDHT();
  readPMS5003();
  publishData();
}

int readDHT() {
  int result = DHT.acquireAndWait(2000);
  if (result >= DHTLIB_OK) {
    temp = DHT.getCelsius();
    hum = DHT.getHumidity();
    result = DHTLIB_OK;
  }
  return result;
}

int readPMS5003() {
  if(dustSensor.listen()) {
    pmsData = dustSensor.readData();
    return 0;
  }
  return -1;
}

void publishData() {
  snprintf(envData, sizeof(envData)
          , "{ \"temp\": %.1f, \"rh\": %.1f, \"pm10\": %u, \"pm25\": %u, \"pm100\": %u }"
          , temp
          , hum
          , pmsData.pm10_standard
          , pmsData.pm25_standard
          , pmsData.pm100_standard
          );
  if (client.isConnected()) {
    client.publish(mqttINFO, envData);
  }
  else {
    client.connect(mqttTOPIC, mqttUSER, mqttPWD);
  }
}
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