aqi/index.js

A JavaScript library to calculate National Air Quality index based on concentrations

var breakpoints = {
	'Carbon Monoxide': ['0.0-1.0', '1.1-2.0', '2.1-10.0', '10.1-17.0', '17.1-34.0'],
	'Nitrogen Dioxide': ['0-40', '41-80', '81-180', '181-280', '281-400'],
	'PM 2dot5': ['0-30', '31-60', '61-90', '91-120', '121-250'],
	'Sulfur Dioxide': ['0-40', '41-80', '81-380', '381-800', '801-1600'],
	'PM10': ['0-50', '51-100', '101-250', '251-350', '351-430'],
	'Ozone': ['0-50', '51-100', '101-168', '169-208', '209-748'],
	'Ammonia': ['0-200', '201-400', '401-800', '801-1200', '1200-1800']
};

var aqi = {
	'Carbon Monoxide': {
		'0.0': 0,
		'1.0': 50,
		'1.1': 51,
		'2.0': 100,
		'2.1': 101,
		'10.0': 200,
		'10.1': 201,
		'17.0': 300,
		'17.1': 301,
		'34.0': 400,
		'34.1': 401,
		'max': 500
	},
	'Nitrogen Dioxide': {
		'0': 0,
		'40': 50,
		'41': 51,
		'80': 100,
		'81': 101,
		'180': 200,
		'181': 201,
		'280': 300,
		'281': 301,
		'400': 400,
		'401': 401,
		'max': 500
	},
	'PM 2dot5': {
		'0': 0,
		'30': 50,
		'31': 51,
		'60': 100,
		'61': 101,
		'90': 200,
		'91': 201,
		'120': 300,
		'121': 301,
		'250': 400,
		'251': 401,
		'max': 500
	},
	'Sulfur Dioxide': {
		'0': 0,
		'40': 50,
		'41': 51,
		'80': 100,
		'81': 101,
		'380': 200,
		'381': 201,
		'800': 300,
		'801': 301,
		'1600': 400,
		'1601': 401,
		'max': 500
	},
	'PM10': {
		'0': 0,
		'50': 50,
		'51': 51,
		'100': 100,
		'101': 101,
		'250': 200,
		'251': 201,
		'350': 300,
		'351': 301,
		'430': 400,
		'431': 401,
		'max': 500
	},
	'Ozone': {
		'0': 0,
		'50': 50,
		'51': 51,
		'100': 100,
		'101': 101,
		'168': 200,
		'169': 201,
		'208': 300,
		'209': 301,
		'748': 400,
		'749': 401,
		'max': 500
	},
	'Ammonia': {
		'0': 0,
		'200': 50,
		'201': 51,
		'400': 100,
		'401': 101,
		'800': 200,
		'801': 201,
		'1200': 300,
		'1201': 301,
		'1800': 400,
		'1801': 401,
		'max': 500
	}
};

module.exports = {
	calculateAqi: function (parameter, concentration) {

		var paramBreakpoints = breakpoints[parameter];
		var paramAqi = aqi[parameter];

		var iP = 0;

		for (var i = 0; i < paramBreakpoints.length; i++) {
			var arrBreakpointRange = paramBreakpoints[i].split('-');
			var bpLow = parseFloat(arrBreakpointRange[0]);
			var bpHigh = parseFloat(arrBreakpointRange[1]);

			if (concentration >= bpLow && concentration <= bpHigh) {
				var iLow = paramAqi[arrBreakpointRange[0]];
				var iHigh = paramAqi[arrBreakpointRange[1]];
				iP = Math.round((((iHigh - iLow) / (bpHigh - bpLow)) * (concentration - bpLow)) + iLow);
				break;
			}
		}

		return iP;
	}
};