Changing land-use and climate may alter emissions of biogenic isoprene, a key ozone (O<sub>3</sub>) precursor. Isoprene is also a precursor to peroxy acetyl nitrate (PAN) and thus affects partitioning among oxidized nitrogen (NO<sub>y</sub>) species, shifting the balance towards PAN which more efficiently contributes to long-range transport relative to nitric acid (HNO<sub>3</sub>) which rapidly deposits. With a suite of sensitivity simulations in the MOZART-2 global tropospheric chemistry model, we gauge the relative importance of the intercontinental influence of 20% changes in North American (NA) isoprene versus 20% changes in NA anthropogenic emissions (nitrogen oxides (NO<sub>x</sub>), non-methane volatile organic compounds (NMVOC) and NO<sub>x</sub> + NMVOC + carbon monoxide + aerosols). The regional NA surface O<sub>3</sub> response to a 20% increase in NA isoprene is approximately one third of the response (oppositely signed) to a 20% decrease in all NA anthropogenic emissions in summer. The intercontinental surface O<sub>3</sub> response over Europe and North Africa (EU region) to NA isoprene is more than half of the response to all NA anthropogenic emissions combined in summer and fall. During these seasons, natural inter-annual variations in NA isoprene emissions (estimated at ±10%) may modulate the responses of EU surface O<sub>3</sub>, lower tropospheric PAN, and total NO<sub>y</sub> deposition to a 20% decrease in NA anthropogenic emissions by ±25%, ±50%, and ±20%, respectively. Lower tropospheric PAN responds similarly for 20% perturbations to either NA isoprene or NA anthropogenic O<sub>3</sub> precursor emissions. This PAN response is at least twice as large as the relative changes in surface O<sub>3</sub>, implying that long-term PAN measurements at high altitude sites may help to detect O<sub>3</sub> precursor emission changes. We find that neither the baseline level of isoprene emissions nor the fate of isoprene nitrates contributes to the large diversity in model estimates of the anthropogenic emission influence on intercontinental surface O<sub>3</sub> or oxidized nitrogen deposition, reported in the recent TF HTAP multi-model studies (TFHTAP, 2007).