Does dew point change with change of ambient temperature?

The dew point temperature depends on 2 parameters: pressure and humidity.

It does not depend on temperature.

You can find it in a diagram where these two lines intersect:

• Constant pressure line (at your level, usually 1atm).
• Constant saturated vapor pressure line.

Because that means that you decrease temperature keeping constant pressure. At some point, lowering temperature like that will end up matching the exact point $(P,T)$ for which your actual humidity is the saturated one. Then water starts condensing.

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A good way to see it is using the mass mixing ratio, which can be easily written in terms of mol mixing ratio:

$$w=frac{m_{vap}}{m_{dryAir}}= frac{n_{vap}}{n_{dryAir}}cdot frac{mm_{vap}}{mm_{dry}}simeq frac{n_{vap}}{n_{dryAir}}cdot 0.622$$

So you can say that $ w= dfrac{n_v}{n_d} cdot 0.622 $, but the moles ratio is the same as the pressure ratio:

$$w= dfrac{P_v}{P_d} cdot 0.622 = dfrac{P_v}{P-P_v} cdot 0.622 $$

There is a particular case, when the pressure is the saturated vapor pressure:

$$w_s= dfrac{P_s}{P-P_s} cdot 0.622 $$

Relative humidity is strongly related to this. In fact,

$$ frac{w}{w_s} = frac{P_v / P_d }{P_s/P_d} = frac{P_v}{P_s}=RH$$

So, once you are given your three parameters: $(P,T, RH)$, you can go on. Humidity must be given anyhow: RH, w, or whatever, but you need to know humidity.

You'll obviously have your dew point when $w$=$w_s$.

So you have a first equation: $w_s=constant$. What constant? The one you're given initially, initial conditions.

So you have that

$$const= dfrac{P_s}{P-P_s} cdot 0.622 $$

and the saturated vapor pressure depends on $T$. A good model is

$$P_s = Acdot e^{-B/T}$$

So now you decrease temperature with constant pressure until water condenses. That's an extra equation: $P=const$. What constant? The one you're given initially.

So you finally have the equation that

$$w_0= dfrac{P_s}{P_0-P_s} cdot 0.622 $$

$$w_0= dfrac{Acdot e^{-B/T_d}}{P_0-Acdot e^{-B/T_d}} cdot 0.622 $$

You can get $T_d$ from here.

The constants are $Asimeq 2.53cdot 10^9 mbar$; $Bsimeq 5240 K$.