Bukayo Saka and Kai Havertz twice hauled Arsenal level in the first half before Trossard's goals put the Gunners in control after the break.

Fabio Vieira added a stunning fifth after Ferran Torres cut the deficit.

Arsenal, Premier League runners-up last season, begin their season on 6 August against Treble winners Manchester City in the Community Shield at Wembley.

At the home of the NFL's Los Angeles Rams and Los Angeles Chargers, Barcelona's Robert Lewandowski opened the scoring after seven minutes when he followed up Raphinha's saved attempt.

Saka slotted in a 13th-minute equaliser, but the England international then sent a penalty wide midway through the first half.

After Raphinha's free-kick deflected in off Martin Odegaard, Arsenal's Norwegian midfielder set up summer signing Havertz to make it 2-2 before the interval.

Winger Trossard rolled the ball into the bottom corner for his first goal after 55 minutes, adding his second with a first-time finish from Kieran Tierney's pass.

Ferran Torres' goal two minutes from time gave Barcelona hope, but Vieira's excellent long-range strike sealed victory for Arsenal.