Update data.

async def update(self):
        """Update data."""
        if self._last_update is None or datetime.datetime.now() - self._last_update > datetime.timedelta(3600):
            try:
                with async_timeout.timeout(10):
                    resp = await self._websession.get(self._api_url, params=self._urlparams)
                if resp.status != 200:
                    _LOGGER.error('%s returned %s', self._api_url, resp.status)
                    return False
                self._data = await resp.json()
            except (asyncio.TimeoutError, aiohttp.ClientError) as err:
                _LOGGER.error('%s returned %s', self._api_url, err)
                return False
        try:
            forecast_time = datetime.datetime.now(pytz.utc) + datetime.timedelta(hours=self._forecast)

            data = None
            min_dist = 24 * 3600
            for _data in self._data['data']['time']:
                valid_from = parse_datetime(_data['from'])
                valid_to = parse_datetime(_data['to'])

                if forecast_time >= valid_to:
                    # Has already passed. Never select this.
                    continue

                average_dist = (abs((valid_to - forecast_time).total_seconds()) +
                                abs((valid_from - forecast_time).total_seconds()))
                if average_dist < min_dist:
                    min_dist = average_dist
                    data = _data
            if not data:
                return False
            self.data['aqi'] = data.get('variables', {}).get('AQI', {}).get('value')
            self.data['pm10_concentration'] = data.get('variables',
                                                       {}).get('pm10_concentration', {}).get('value')
            self.data['o3_concentration'] = data.get('variables',
                                                     {}).get('o3_concentration', {}).get('value')
            self.data['no2_concentration'] = data.get('variables',
                                                      {}).get('no2_concentration', {}).get('value')
            self.data['pm25_concentration'] = data.get('variables',
                                                       {}).get('pm25_concentration', {}).get('value')
            self.data['location'] = "{}, {}".format(self._data.get('meta', {}).get('location', {}).get('name'),
                                                    self._data.get('meta', {}).get('superlocation', {}).get('name'))
            state = data.get('variables', {}).get('AQI', {}).get('value')
            if state < 2:
                level = "low"
            elif state < 3:
                level = "medium"
            else:
                level = "high"
            self.data['level'] = level

            self.units['aqi'] = data.get('variables', {}).get('AQI', {}).get('units')
            self.units['pm10_concentration'] = data.get('variables',
                                                        {}).get('pm10_concentration', {}).get('units')
            self.units['o3_concentration'] = data.get('variables',
                                                      {}).get('o3_concentration', {}).get('units')
            self.units['no2_concentration'] = data.get('variables',
                                                       {}).get('no2_concentration', {}).get('units')
            self.units['pm25_concentration'] = data.get('variables',
                                                        {}).get('pm25_concentration', {}).get('units')
            self.units['aqi'] = data.get('variables', {}).get('AQI', {}).get('value')

        except IndexError as err:
            _LOGGER.error('%s returned %s', resp.url, err)
            return False
        return True