amcharts 的问题 amcharts 的问题

var chartOptions = {
"type": "serial",
"pathToImages": "http://cdn.amcharts.com/lib/3/images/",
"categoryField": "date",
"rotate": false,
"startDuration": 1,
"categoryAxis": {
"gridPosition": "start",
"position": "left"
},
"trendLines": [],
"guides": [],
"valueAxes": [{
"axisAlpha": 0,
"position": "left",
"title": “24hr-PM¹⁰”
}],
"allLabels": [],
"amExport": {
"right": 20,
"top": 20
},
"balloon": {},
"titles": []};

        怎么样让 "title": “24hr-PM<sup>10</sup>” 这个title的<sup>标签起作用