CQ1 wasn't declared in this scope

hey,guys im working on a air quality monitoring project and something went awfully wrong with my code.
it keeps saying CQ1 wasn't declared in the scope and i couldn't figure out how deal with it. plz help, really appreciate your answer.
#include"AirQuality.h"
#include"Arduino.h"
AirQuality airqualitysensor;
int current_quality = -1;

int pin = 8;
unsigned long duration;
unsigned long starttime;
unsigned long sampletime_ms = 3000;//sampe 30s ;
unsigned long lowpulseoccupancy = 0;
float ratio = 0;
float concentration = 0;

void setup()
{
Serial.begin(9600);
pinMode(8, INPUT);
starttime = millis();//get the current time;
airqualitysensor.init(A0);
}
void loop()
{
duration = pulseIn(pin, LOW);
lowpulseoccupancy = lowpulseoccupancy + duration;
Serial.print(0);
if ((millis() - starttime) >= sampletime_ms) //if the sampel time = = 30s
{
ratio = lowpulseoccupancy / (sampletime_ms * 10.0); // Integer percentage 0=>100
concentration = 1.1 * pow(ratio, 3) - 3.8 * pow(ratio, 2) + 520 * ratio + 0.62; // using spec sheet curve
// Serial.print("concentration = ");
// Serial.print(concentration);
// Serial.println(" pcs/0.01cf");
// Serial.println("\n");
lowpulseoccupancy = 0;
starttime = millis();
}

current_quality = airqualitysensor.slope();
if (current_quality >= 0)// if a valid data returned.
{
if (current_quality == 0)
//Serial.println("High pollution! Force signal active");
Serial.print(CQ1);
else if (current_quality == 1)
//Serial.println("High pollution!");
Serial.print(CQ2);
else if (current_quality == 2)
//Serial.println("Low pollution!");
Serial.print(CQ3);
else if (current_quality == 3)
//Serial.println("Fresh air");
Serial.print(CQ4);

}

}
ISR(TIMER1_OVF_vect)
{
if (airqualitysensor.counter == 61) //set 2 seconds as a detected duty
{

airqualitysensor.last_vol = airqualitysensor.first_vol;
airqualitysensor.first_vol = analogRead(A0);
airqualitysensor.counter = 0;
airqualitysensor.timer_index = 1;
PORTB = PORTB ^ 0x20;
}
else
{
airqualitysensor.counter++;
}
}

On this line you attempt to print a variable named CQ1

Serial.print(CQ1);

You have not defined nor declared any variable named CQ1 anywhere in your sketch, nor is it defined in the library (assuming that's the grove air quality library). Same goes for where you're printing CQ2, CQ3, and CQ4. Do you mean to print the text "CQ1"? In that case you forgot the quotes.

Its the arduino side of the code. Basically datas were gathered by arduino and another set of code read into arduino's serial monitor and shows the graphic

i added the quotes and the verification was successful
then while i was trying to upload the code to arudino,
this appears
avrdude: ser_setspeed(): tcsetattr() failed
avrdude: ser_open(): can't set attributes for device "/dev/cu.usbmodem1421": Invalid argument
ioctl("TIOCMGET"): Bad file descriptor