Plots renders exponents not correctly(?)

Dear all,

I try to plot (Plots, GR) some curves with a y-label that contains an exponent.

plot_3 = plot(Time, N, title = "Runs with BNF and Reduction in Oceans",
    title_location = :center,
    label = "",
    xlabel = "Myr ago",
    ylabel = "atm. nitrogen amount / 10^{9} Tg",
    xflip = true,
    legend = false,
    minorticks = 5,
    linestyle = :dash,
    left_margin = l_margin, bottom_margin = b_margin, top_margin = t_margin, right_margin = r_margin, color = col[1])

plot(plot_2,plot_3,layout = (1,2))


Well, the exponent is shown correctly in the Atom plot pane, but not in the final file. Can anybody help me there? The attached figure should explain what I mean.

If required, here is the style of my plots:

using Plots, Plots.PlotMeasures
    sX = 630 # 630
    sY = 315 # 315
    sD = 300
    sT = "Calibri"
    sT1 = 8
    sT2 = 7
    l_margin = [0px 0px]
    b_margin = [4px 0px]
    t_margin = [2px 0px]
    r_margin = [-6px 0px]
    col = [:blue :cyan :gold :red :green :black :orange :red :black :limegreen :darkturquoise :navy :blueviolet :navajowhite3 :magenta :red :goldenrod1 :lightcoral :orangered4]
    default(size=(sX,sY), dpi=sD, titlefont=(sT1,sT), guidefont=(sT2,sT), tickfont=(sT2,sT), legendfont=(sT2,sT), framestyle = :box, seriescolor = col)

Btw.: The layout style with 2 plots in one figure is not the reason; I tried it out several times.

Thanks for reading and, in advance, for your support.